New translations app_en.arb (Spanish)

[ci skip]
2026-07-03 11:18:04 +02:00 · 2026-07-03 04:25:28 +07:00 · 2026-07-03 03:26:55 +07:00 · 2026-07-03 01:58:22 +07:00 · 2026-07-03 00:04:38 +07:00 · 2026-07-02 21:58:18 +07:00
326 changed files with 164931 additions and 35785 deletions
@@ -1,3 +1,3 @@
 {
-  "flutter": "3.41.4"
+  "flutter": "3.41.5"
 }
@@ -4,5 +4,5 @@ contact_links:
    url: https://github.com/zarzet/SpotiFLAC-Mobile#readme
    about: Check the README for setup instructions and FAQ
  - name: Extension Development Guide
-    url: https://zarz.moe/docs
+    url: https://spotiflac.zarz.moe/docs
    about: Documentation for building SpotiFLAC extensions
@@ -71,7 +71,7 @@ jobs:
      - name: Setup Go
        uses: actions/setup-go@v6
        with:
-          go-version: "1.25.7"
+          go-version: "1.25.8"
          cache-dependency-path: go_backend/go.sum

      # Cache Gradle for faster builds
@@ -93,12 +93,12 @@ jobs:
          # Accept licenses
          yes | $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager --licenses || true

-          # Install NDK r27d LTS (required for 16KB page size support on Android 15+)
+          # Install NDK r29 (supports 16KB page size for Android 15+)
          # Platform android-36 and build-tools 36.0.0 for targetSdk 36 (Android 16)
-          $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager "ndk;27.3.13750724" "platforms;android-36" "build-tools;36.0.0"
+          $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager "ndk;29.0.14206865" "platforms;android-36" "build-tools;36.0.0"

          # Set NDK path
-          echo "ANDROID_NDK_HOME=$ANDROID_HOME/ndk/27.3.13750724" >> $GITHUB_ENV
+          echo "ANDROID_NDK_HOME=$ANDROID_HOME/ndk/29.0.14206865" >> $GITHUB_ENV

      - name: Install gomobile
        run: |
@@ -164,17 +164,22 @@ jobs:
          path: build/app/outputs/flutter-apk/SpotiFLAC-*.apk

  build-ios:
-    runs-on: macos-latest
+    runs-on: macos-15
    needs: get-version # Only depends on version, NOT android build!

    steps:
      - name: Checkout repository
        uses: actions/checkout@v6

+      - name: Select Xcode 26.1.1
+        run: |
+          sudo xcode-select -s /Applications/Xcode_26.1.1.app
+          xcodebuild -version
+
      - name: Setup Go
        uses: actions/setup-go@v6
        with:
-          go-version: "1.25.7"
+          go-version: "1.25.8"
          cache-dependency-path: go_backend/go.sum

      # Cache CocoaPods
@@ -252,6 +257,15 @@ jobs:
      - name: Get Flutter dependencies
        run: flutter pub get

+      - name: Normalize ffmpeg plugin shell scripts (strip CRLF)
+        run: |
+          find "$HOME/.pub-cache/hosted" -path "*ffmpeg_kit_flutter_new_full*/scripts/*.sh" -type f -print0 |
+            while IFS= read -r -d '' f; do
+              perl -pi -e 's/\r$//' "$f"
+              chmod +x "$f"
+              echo "Normalized line endings: $f"
+            done
+
      - name: Generate app icons
        run: dart run flutter_launcher_icons

@@ -44,6 +44,7 @@ go_backend/*.xcframework/
 # Android
 android/.gradle/
 android/app/libs/gobackend.aar
+android/app/libs/gobackend-sources.jar
 android/local.properties
 android/*.iml
 android/key.properties
@@ -57,7 +58,6 @@ ios/Pods/
 ios/.symlinks/
 ios/Flutter/Flutter.framework/
 ios/Flutter/Flutter.podspec
-android/app/libs/gobackend-sources.jar

 # Extension folder
 extension/
@@ -66,8 +66,12 @@ extension/
 AGENTS.md

 # Temp/misc
+.tmp/
 nul
+NUL
 network_requests.txt
+*.bak
+/AndroidManifest.xml

 # Log files
 *.log
@@ -77,6 +81,7 @@ flutter_*.log
 # Development tools
 tool/
 .claude/settings.local.json
+.playwright-mcp/

 # FVM Version Cache
 .fvm/
@@ -86,7 +86,7 @@ Translation files are located in `lib/l10n/arb/`.
   git remote add upstream https://github.com/zarzet/SpotiFLAC-Mobile.git
   ```

-3. **Use FVM (Flutter Version: 3.38.1)**
+3. **Use FVM (Flutter Version: 3.41.5)**
   ```bash
   fvm use
   ```
@@ -1,14 +1,14 @@
 <div align="center">

 <picture>
-  <source media="(prefers-color-scheme: dark)" srcset="assets/images/banner-readme-dark.png">
-  <source media="(prefers-color-scheme: light)" srcset="assets/images/banner-readme-light.png">
-  <img alt="SpotiFLAC Mobile" src="assets/images/banner-readme-light.png" width="650" height="auto">
+  <source media="(prefers-color-scheme: dark)" srcset="assets/readme/banner-readme-dark.png">
+  <source media="(prefers-color-scheme: light)" srcset="assets/readme/banner-readme-light.png">
+  <img alt="SpotiFLAC Mobile" src="assets/readme/banner-readme-light.png" width="650" height="auto">
 </picture>

 <p align="center">
-  <a href="https://trendshift.io/repositories/17247">
-    <img src="https://trendshift.io/api/badge/repositories/17247" alt="zarzet%2FSpotiFLAC-Mobile | Trendshift" width="250" height="55">
+  <a href="https://trendshift.io/repositories/25971" target="_blank">
+    <img src="https://trendshift.io/api/badge/repositories/25971" alt="spotiflacapp%2FSpotiFLAC-Mobile | Trendshift" width="250" height="55">
  </a>
 </p>

@@ -17,7 +17,7 @@
 <div align="center">

 [![GitHub Release](https://img.shields.io/github/v/release/zarzet/SpotiFLAC-Mobile?style=for-the-badge&logo=github)](https://github.com/zarzet/SpotiFLAC-Mobile/releases)
-[![VirusTotal](https://img.shields.io/badge/VirusTotal-Safe-brightgreen?style=for-the-badge&logo=virustotal)](https://www.virustotal.com/gui/file/cc11355330c76f97548b8d26452b91746db9d9c1edbcfc4c18250133484d1487)
+[![VirusTotal](https://img.shields.io/badge/VirusTotal-Safe-brightgreen?style=for-the-badge&logo=virustotal)](https://www.virustotal.com/gui/file/31d1bf3c3b2015c13e83c4f909a7c6093a9423e3e702f0c582a3e0035c849424)
 [![Crowdin](https://img.shields.io/badge/HELP%20TRANSLATE%20ON-CROWDIN-%2321252b?style=for-the-badge&logo=crowdin)](https://crowdin.com/project/spotiflac-mobile)

 [![Telegram Channel](https://img.shields.io/badge/CHANNEL-2CA5E0?style=for-the-badge&logo=telegram&logoColor=white)](https://t.me/spotiflac)
@@ -28,10 +28,10 @@
 ## Screenshots

 <p align="center">
-  <img src="assets/images/1.jpg?v=2" width="200" />
-  <img src="assets/images/2.jpg?v=2" width="200" />
-  <img src="assets/images/3.jpg?v=2" width="200" />
-  <img src="assets/images/4.jpg?v=2" width="200" />
+  <img src="assets/readme/1.jpg?v=2" width="200" />
+  <img src="assets/readme/2.jpg?v=2" width="200" />
+  <img src="assets/readme/3.jpg?v=2" width="200" />
+  <img src="assets/readme/4.jpg?v=2" width="200" />
 </p>

 ---
@@ -59,7 +59,7 @@ Extensions let the community add new music sources and features without waiting
 ## Related Projects

 ### [SpotiFLAC (Desktop)](https://github.com/afkarxyz/SpotiFLAC)
-Download music in true lossless FLAC from Tidal, Qobuz & Amazon Music available for Windows, macOS & Linux.
+Download music in true lossless FLAC from extension-provided sources on Windows, macOS & Linux.

 ### [SpotiFLAC (Python Module)](https://github.com/ShuShuzinhuu/SpotiFLAC-Module-Version)
 Python library for SpotiFLAC integration, maintained by [@ShuShuzinhuu](https://github.com/ShuShuzinhuu).
@@ -80,7 +80,7 @@ Starting from version 3.8.0, SpotiFLAC uses a decentralized extension repository
 <summary><b>Why is my download failing with "Song not found"?</b></summary>
 <br>

-The track may not be available on the streaming services. Try enabling more providers under **Settings > Download > Provider Priority**, or install additional extensions like Amazon Music from the Store.
+The track may not be available from your enabled providers. Try enabling more providers under **Settings > Extensions > Provider Priority**, or install additional download extensions from the Store.

 </details>

@@ -88,10 +88,7 @@ The track may not be available on the streaming services. Try enabling more prov
 <summary><b>Why are some tracks downloading in lower quality?</b></summary>
 <br>

-Quality depends on what's available from the streaming service and its extensions. Built-in providers:
- **Tidal** up to 24-bit/192kHz
- **Qobuz** up to 24-bit/192kHz
- **Deezer** up to 16-bit/44.1kHz
+Quality depends on what's available from the source and the installed download extension. Check each extension's quality options and service notes in the app.

 </details>

@@ -141,6 +138,11 @@ In AltStore/SideStore, go to **Browse > Sources**, tap **+**, and paste the link

 </details>

+> [!NOTE]
+> If SpotiFLAC is useful to you, consider supporting development:
+>
+> [![Ko-fi](https://ko-fi.com/img/githubbutton_sm.svg)](https://ko-fi.com/zarzet)
+
 ---

 ## Contributors
@@ -161,14 +163,21 @@ Interested in contributing? Check out the [Contributing Guide](CONTRIBUTING.md)

 | | | | | |
 |---|---|---|---|---|
-| [hifi-api](https://github.com/binimum/hifi-api) | [music.binimum.org](https://music.binimum.org) | [qqdl.site](https://qqdl.site) | [squid.wtf](https://squid.wtf) | [spotisaver.net](https://spotisaver.net) |
-| [dabmusic.xyz](https://dabmusic.xyz) | [AfkarXYZ](https://github.com/afkarxyz) | [LRCLib](https://lrclib.net) | [Paxsenix](https://lyrics.paxsenix.org) | [Cobalt](https://cobalt.tools) |
-| [qwkuns.me](https://qwkuns.me) | [SpotubeDL](https://spotubedl.com) | [Song.link](https://song.link) | [IDHS](https://github.com/sjdonado/idonthavespotify) | |
+| [MusicDL](https://www.musicdl.me) | [LRCLib](https://lrclib.net) | [Paxsenix](https://lyrics.paxsenix.org) | [Cobalt](https://cobalt.tools) | [Song.link](https://song.link) |
+| [IDHS](https://github.com/sjdonado/idonthavespotify) |  |  |  |  |

-> [!NOTE]
-> If SpotiFLAC is useful to you, consider supporting development:
->
-> [![Ko-fi](https://ko-fi.com/img/githubbutton_sm.svg)](https://ko-fi.com/zarzet)
+---
+
+## Disclaimer
+
+This repository and its contents are provided strictly for educational and research purposes. The software is provided "as-is" without warranty of any kind, express or implied, as stated in the [MIT License](LICENSE).
+
+- No copyrighted content is hosted, stored, mirrored, or distributed by this repository.
+- Users must ensure that their use of this software is properly authorized and complies with all applicable laws, regulations, and third-party terms of service.
+- This software is provided free of charge by the maintainer. If you paid a third party for access to this software in its original form from this repository, you may have been misled or scammed. Any redistribution or commercial use by third parties must comply with the terms of the repository license. No affiliation, endorsement, or support by the maintainer is implied unless explicitly stated in writing.
+- SpotiFLAC Mobile is an independent project. It is not affiliated with, endorsed by, or connected to any other project or version on other platforms that may share a similar name. The maintainer of this repository has no control over or responsibility for third-party projects.
+- The author(s) disclaim all liability for any direct, indirect, incidental, or consequential damages arising from the use or misuse of this software. Users assume all risk associated with its use.
+- If you are a copyright holder or authorized representative and believe this repository infringes upon your rights, please contact the maintainer with sufficient detail (including relevant URLs and proof of ownership). The matter will be promptly investigated and appropriate action will be taken, which may include removal of the referenced material.

 > [!TIP]
 > **Star the repo** to get notified about all new releases directly from GitHub.
@@ -9,6 +9,19 @@
 # packages, and plugins designed to encourage good coding practices.
 include: package:flutter_lints/flutter.yaml

+plugins:
+  riverpod_lint: 3.1.4-dev.3
+
+analyzer:
+  exclude:
+    - build/**
+    - .dart_tool/**
+    - lib/**/*.g.dart
+    - lib/l10n/*.dart
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true
 linter:
  # The lint rules applied to this project can be customized in the
  # section below to disable rules from the `package:flutter_lints/flutter.yaml`
@@ -23,6 +36,13 @@ linter:
  rules:
    # avoid_print: false  # Uncomment to disable the `avoid_print` rule
    # prefer_single_quotes: true  # Uncomment to enable the `prefer_single_quotes` rule
+    always_declare_return_types: true
+    avoid_dynamic_calls: true
+    avoid_types_as_parameter_names: true
+    strict_top_level_inference: true
+    type_annotate_public_apis: true
+    cancel_subscriptions: true
+    close_sinks: true

 # Additional information about this file can be found at
 # https://dart.dev/guides/language/analysis-options
@@ -1,71 +0,0 @@
-plugins {
-    id "com.android.application"
-    id "kotlin-android"
-    id "dev.flutter.flutter-gradle-plugin"
-}
-
-def localProperties = new Properties()
-def localPropertiesFile = rootProject.file('local.properties')
-if (localPropertiesFile.exists()) {
-    localPropertiesFile.withReader('UTF-8') { reader ->
-        localProperties.load(reader)
-    }
-}
-
-def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
-if (flutterVersionCode == null) {
-    flutterVersionCode = '1'
-}
-
-def flutterVersionName = localProperties.getProperty('flutter.versionName')
-if (flutterVersionName == null) {
-    flutterVersionName = '1.0'
-}
-
-android {
-    namespace "com.zarz.spotiflac"
-    compileSdk flutter.compileSdkVersion
-    ndkVersion flutter.ndkVersion
-
-    compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_8
-        targetCompatibility JavaVersion.VERSION_1_8
-    }
-
-    kotlinOptions {
-        jvmTarget = '1.8'
-    }
-
-    sourceSets {
-        main.java.srcDirs += 'src/main/kotlin'
-    }
-
-    defaultConfig {
-        applicationId "com.zarz.spotiflac"
-        minSdkVersion flutter.minSdkVersion
-        targetSdk flutter.targetSdkVersion
-        versionCode flutterVersionCode.toInteger()
-        versionName flutterVersionName
-    }
-
-    buildTypes {
-        release {
-            signingConfig signingConfigs.debug
-            minifyEnabled false
-            shrinkResources false
-        }
-    }
-}
-
-flutter {
-    source '../..'
-}
-
-dependencies {
-    // Go backend library (gomobile generated)
-    implementation fileTree(dir: 'libs', include: ['*.aar'])
-    
-    // Kotlin coroutines for async Go backend calls
-    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3'
-    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.3'
-}
@@ -20,6 +20,10 @@ android {
    compileSdk = flutter.compileSdkVersion
    ndkVersion = flutter.ndkVersion

+    buildFeatures {
+        buildConfig = true
+    }
+
    compileOptions {
        isCoreLibraryDesugaringEnabled = true
        sourceCompatibility = JavaVersion.VERSION_17
@@ -57,6 +61,18 @@ android {
    }

    buildTypes {
+        getByName("debug") {
+            ndk {
+                debugSymbolLevel = "FULL"
+            }
+        }
+
+        getByName("profile") {
+            ndk {
+                debugSymbolLevel = "FULL"
+            }
+        }
+
        release {
            // For local builds: use release signing if key.properties exists
            // For CI builds: APK is signed by GitHub Action after build
@@ -71,6 +87,9 @@ android {
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
+            ndk {
+                debugSymbolLevel = "FULL"
+            }
        }
    }
    
@@ -101,8 +120,9 @@ dependencies {
    // Include all AAR and JAR files from libs folder
    implementation(fileTree(mapOf("dir" to "libs", "include" to listOf("*.jar", "*.aar"))))
    
-    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.10.2")
-    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.10.0")
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.11.0")
+    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.11.0-beta02")
    implementation("androidx.documentfile:documentfile:1.1.0")
-    implementation("androidx.activity:activity-ktx:1.12.3")
+    implementation("androidx.activity:activity-ktx:1.13.0")
+    implementation("com.antonkarpenko:ffmpeg-kit-full:2.1.0")
 }
@@ -18,7 +18,7 @@
    <uses-permission android:name="android.permission.WAKE_LOCK" />

    <application
-        android:label="SpotiFLAC"
+        android:label="SpotiFLAC Mobile"
        android:name="${applicationName}"
        android:icon="@mipmap/ic_launcher"
        android:usesCleartextTraffic="false"
@@ -86,6 +86,20 @@
                <category android:name="android.intent.category.BROWSABLE" />
                <data android:scheme="https" android:host="music.youtube.com" />
            </intent-filter>
+
+            <!-- Extension OAuth (PKCE) redirect: spotiflac://callback?code=...&state=<extension_id> -->
+            <intent-filter>
+                <action android:name="android.intent.action.VIEW" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <category android:name="android.intent.category.BROWSABLE" />
+                <data android:scheme="spotiflac" android:host="callback" />
+            </intent-filter>
+            <intent-filter>
+                <action android:name="android.intent.action.VIEW" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <category android:name="android.intent.category.BROWSABLE" />
+                <data android:scheme="spotiflac" android:host="spotify-callback" />
+            </intent-filter>
        </activity>

        <!-- Download Service -->
@@ -94,24 +108,6 @@
            android:exported="false"
            android:foregroundServiceType="dataSync" />

-        <!-- Audio playback service for media notification / background audio -->
-        <service
-            android:name="com.ryanheise.audioservice.AudioService"
-            android:exported="true"
-            android:foregroundServiceType="mediaPlayback">
-            <intent-filter>
-                <action android:name="android.media.browse.MediaBrowserService" />
-            </intent-filter>
-        </service>
-
-        <receiver
-            android:name="com.ryanheise.audioservice.MediaButtonReceiver"
-            android:exported="true">
-            <intent-filter>
-                <action android:name="android.intent.action.MEDIA_BUTTON" />
-            </intent-filter>
-        </receiver>
-
        <!-- flutter_local_notifications receivers -->
        <receiver android:exported="false" android:name="com.dexterous.flutterlocalnotifications.ScheduledNotificationReceiver" />
        <receiver android:exported="false" android:name="com.dexterous.flutterlocalnotifications.ScheduledNotificationBootReceiver">
@@ -1,5 +0,0 @@
-package com.example.temp_project
-
-import io.flutter.embedding.android.FlutterActivity
-
-class MainActivity : FlutterActivity()
@@ -0,0 +1,496 @@
+package com.zarz.spotiflac
+
+import android.content.Context
+import android.net.Uri
+import android.util.Log
+import androidx.documentfile.provider.DocumentFile
+import org.json.JSONObject
+import java.io.File
+import java.util.Locale
+
+/**
+ * Shared SAF download wrapper for foreground activity calls and service-owned
+ * native workers.
+ */
+object SafDownloadHandler {
+    private val safDirLock = Any()
+    private const val MAX_SAF_DISPLAY_NAME_UTF8_BYTES = 180
+    private const val STAGED_SAF_MIME_TYPE = "application/octet-stream"
+
+    fun handle(context: Context, requestJson: String, downloader: (String) -> String): String {
+        val req = JSONObject(requestJson)
+        val storageMode = req.optString("storage_mode", "")
+        val treeUriStr = req.optString("saf_tree_uri", "")
+        if (storageMode != "saf" || treeUriStr.isBlank()) {
+            return downloader(requestJson)
+        }
+
+        val treeUri = Uri.parse(treeUriStr)
+        val relativeDir = sanitizeRelativeDir(req.optString("saf_relative_dir", ""))
+        val outputExt = normalizeExt(req.optString("saf_output_ext", ""))
+        val mimeType = mimeTypeForExt(outputExt)
+        val fileName = buildSafFileName(req, outputExt)
+        val deferSafPublish = req.optBoolean("defer_saf_publish", false)
+        val useStagedOutput = req.optBoolean("stage_saf_output", false) && !deferSafPublish
+        val stagedFileName = if (useStagedOutput) buildStagedSafFileName(fileName) else fileName
+        val stagedMimeType = if (useStagedOutput) STAGED_SAF_MIME_TYPE else mimeType
+
+        val existingDir = findDocumentDir(context, treeUri, relativeDir)
+        if (existingDir != null) {
+            val existing = existingDir.findFile(fileName)
+            if (existing != null && existing.isFile && existing.length() > 0) {
+                if (useStagedOutput || deferSafPublish) {
+                    deleteStaleStagedFiles(existingDir, fileName, outputExt)
+                }
+                val obj = JSONObject()
+                obj.put("success", true)
+                obj.put("message", "File already exists")
+                obj.put("file_path", existing.uri.toString())
+                obj.put("file_name", existing.name ?: fileName)
+                obj.put("already_exists", true)
+                return obj.toString()
+            }
+        }
+
+        val targetDir = ensureDocumentDir(context, treeUri, relativeDir)
+            ?: return errorJson("Failed to access SAF directory")
+
+        if (deferSafPublish) {
+            deleteStaleStagedFiles(targetDir, fileName, outputExt)
+            val workingExt = outputExt.ifBlank { ".tmp" }
+            val workingFile = File.createTempFile("native_saf_work_", workingExt, context.cacheDir)
+            Log.i("SpotiFLAC", "SAF deferred native output: target=$fileName working=${workingFile.name}")
+            return try {
+                req.put("output_path", workingFile.absolutePath)
+                req.put("output_ext", outputExt)
+                req.remove("output_fd")
+                val response = downloader(req.toString())
+                val respObj = JSONObject(response)
+                if (respObj.optBoolean("success", false)) {
+                    val reportedPath = respObj.optString("file_path", "").trim()
+                    if (reportedPath.isEmpty() || reportedPath.startsWith("/proc/self/fd/")) {
+                        respObj.put("file_path", workingFile.absolutePath)
+                    } else if (reportedPath != workingFile.absolutePath) {
+                        workingFile.delete()
+                    }
+                    respObj.put("file_name", respObj.optString("file_name", "").ifBlank { fileName })
+                    respObj.put("saf_deferred_publish", true)
+                    respObj.put("saf_final_file_name", fileName)
+                    respObj.put("saf_relative_dir", relativeDir)
+                    respObj.put("saf_tree_uri", treeUriStr)
+                    respObj.put("saf_output_ext", outputExt)
+                    respObj.put("saf_final_mime_type", mimeType)
+                } else {
+                    workingFile.delete()
+                }
+                respObj.toString()
+            } catch (e: Exception) {
+                workingFile.delete()
+                errorJson("SAF deferred download failed: ${e.message}")
+            }
+        }
+
+        var document = createOrReuseDocumentFile(targetDir, stagedMimeType, stagedFileName)
+            ?: return errorJson("Failed to create SAF file")
+
+        val pfd = context.contentResolver.openFileDescriptor(document.uri, "rw")
+            ?: return errorJson("Failed to open SAF file")
+
+        var detachedFd: Int? = null
+        try {
+            detachedFd = pfd.detachFd()
+            req.put("output_path", "")
+            req.put("output_fd", detachedFd)
+            req.put("output_ext", outputExt)
+            val response = downloader(req.toString())
+            val respObj = JSONObject(response)
+            if (respObj.optBoolean("success", false)) {
+                val goFilePath = respObj.optString("file_path", "")
+                if (goFilePath.isNotEmpty() &&
+                    !goFilePath.startsWith("content://") &&
+                    !goFilePath.startsWith("/proc/self/fd/")
+                ) {
+                    try {
+                        val srcFile = File(goFilePath)
+                        if (!srcFile.exists() || srcFile.length() <= 0) {
+                            throw IllegalStateException("extension output missing or empty: $goFilePath")
+                        }
+                        val actualExt = normalizeExt(srcFile.extension)
+                        if (actualExt.isNotBlank()) {
+                            respObj.put("actual_extension", actualExt)
+                        }
+                        if (actualExt.isNotBlank() && actualExt != outputExt) {
+                            val actualFileName = buildSafFileName(req, actualExt)
+                            val actualStagedFileName = if (useStagedOutput) {
+                                buildStagedSafFileName(actualFileName)
+                            } else {
+                                actualFileName
+                            }
+                            val actualMimeType = mimeTypeForExt(actualExt)
+                            val replacement = createOrReuseDocumentFile(
+                                targetDir,
+                                if (useStagedOutput) STAGED_SAF_MIME_TYPE else actualMimeType,
+                                actualStagedFileName
+                            ) ?: throw IllegalStateException(
+                                "failed to create SAF output with actual extension"
+                            )
+                            if (replacement.uri != document.uri) {
+                                document.delete()
+                                document = replacement
+                            }
+                        }
+                        context.contentResolver.openOutputStream(document.uri, "wt")?.use { output ->
+                            srcFile.inputStream().use { input ->
+                                input.copyTo(output)
+                            }
+                        } ?: throw IllegalStateException("failed to open SAF output stream")
+                        srcFile.delete()
+                    } catch (e: Exception) {
+                        document.delete()
+                        android.util.Log.w(
+                            "SpotiFLAC",
+                            "Failed to copy extension output to SAF: ${e.message}"
+                        )
+                        return errorJson("Failed to copy extension output to SAF: ${e.message}")
+                    }
+                }
+                respObj.put("file_path", document.uri.toString())
+                respObj.put("file_name", document.name ?: fileName)
+                if (useStagedOutput) {
+                    respObj.put("saf_staged_output", true)
+                    respObj.put("saf_staged_file_name", document.name ?: stagedFileName)
+                }
+            } else {
+                document.delete()
+            }
+            return respObj.toString()
+        } catch (e: Exception) {
+            document.delete()
+            return errorJson("SAF download failed: ${e.message}")
+        } finally {
+            if (detachedFd == null) {
+                try {
+                    pfd.close()
+                } catch (_: Exception) {
+                }
+            }
+        }
+    }
+
+    fun copyContentUriToTemp(context: Context, uriStr: String): String? {
+        return try {
+            val uri = Uri.parse(uriStr)
+            val extension = DocumentFile.fromSingleUri(context, uri)
+                ?.name
+                ?.substringAfterLast('.', "")
+                ?.takeIf { it.isNotBlank() }
+                ?.let { ".$it" }
+                ?: ".tmp"
+            val temp = File.createTempFile("native_saf_", extension, context.cacheDir)
+            context.contentResolver.openInputStream(uri)?.use { input ->
+                temp.outputStream().use { output ->
+                    input.copyTo(output)
+                }
+            } ?: return null
+            temp.absolutePath
+        } catch (e: Exception) {
+            android.util.Log.w("SpotiFLAC", "Failed to copy SAF URI to temp: ${e.message}")
+            null
+        }
+    }
+
+    fun writeFileToSaf(
+        context: Context,
+        treeUriStr: String,
+        relativeDir: String,
+        fileName: String,
+        mimeType: String,
+        srcPath: String
+    ): String? {
+        var stagedDocument: DocumentFile? = null
+        return try {
+            val treeUri = Uri.parse(treeUriStr)
+            val targetDir = ensureDocumentDir(context, treeUri, relativeDir) ?: return null
+            val finalName = sanitizeFilename(fileName)
+            val ext = normalizeExt(finalName.substringAfterLast('.', ""))
+            val stagedName = buildStagedSafFileName(finalName)
+            deleteStaleStagedFiles(targetDir, finalName, ext)
+            val document = createOrReuseDocumentFile(targetDir, STAGED_SAF_MIME_TYPE, stagedName)
+                ?: return null
+            stagedDocument = document
+            val outputStream = context.contentResolver.openOutputStream(document.uri, "wt")
+            if (outputStream == null) {
+                document.delete()
+                stagedDocument = null
+                return null
+            }
+            outputStream.use { output ->
+                File(srcPath).inputStream().use { input ->
+                    input.copyTo(output)
+                }
+            }
+
+            val existingFinal = targetDir.findFile(finalName)
+            if (existingFinal != null && existingFinal.uri != document.uri) {
+                existingFinal.delete()
+            }
+            if (!document.renameTo(finalName)) {
+                document.delete()
+                return null
+            }
+            stagedDocument = null
+            targetDir.findFile(finalName)?.uri?.toString() ?: document.uri.toString()
+        } catch (e: Exception) {
+            stagedDocument?.delete()
+            android.util.Log.w("SpotiFLAC", "Failed to write file to SAF: ${e.message}")
+            null
+        }
+    }
+
+    fun deleteContentUri(context: Context, uriStr: String): Boolean {
+        return try {
+            DocumentFile.fromSingleUri(context, Uri.parse(uriStr))?.delete() == true
+        } catch (_: Exception) {
+            false
+        }
+    }
+
+    private fun normalizeExt(ext: String?): String {
+        if (ext.isNullOrBlank()) return ""
+        return if (ext.startsWith(".")) {
+            ext.lowercase(Locale.ROOT)
+        } else {
+            ".${ext.lowercase(Locale.ROOT)}"
+        }
+    }
+
+    private fun mimeTypeForExt(ext: String?): String {
+        return when (normalizeExt(ext)) {
+            ".m4a", ".mp4" -> "audio/mp4"
+            ".mp3" -> "audio/mpeg"
+            ".opus" -> "audio/ogg"
+            ".flac" -> "audio/flac"
+            ".lrc" -> "application/octet-stream"
+            else -> "application/octet-stream"
+        }
+    }
+
+    private fun forceFilenameExt(name: String, outputExt: String): String {
+        val normalizedExt = normalizeExt(outputExt)
+        if (normalizedExt.isBlank()) return sanitizeFilename(name)
+
+        val safeName = sanitizeFilename(name)
+        val lower = safeName.lowercase(Locale.ROOT)
+        val knownExts = listOf(".flac", ".m4a", ".mp4", ".mp3", ".opus", ".lrc")
+        for (knownExt in knownExts) {
+            if (lower.endsWith(knownExt)) {
+                return safeName.dropLast(knownExt.length) + normalizedExt
+            }
+        }
+        return safeName + normalizedExt
+    }
+
+    private fun buildStagedSafFileName(fileName: String): String {
+        val safeName = sanitizeFilename(fileName)
+        return "$safeName.partial"
+    }
+
+    private fun buildLegacyStagedSafFileName(fileName: String, outputExt: String): String {
+        val safeName = sanitizeFilename(fileName)
+        val ext = normalizeExt(outputExt)
+        if (ext.isNotBlank() && safeName.lowercase(Locale.ROOT).endsWith(ext)) {
+            return safeName.dropLast(ext.length).trimEnd('.', ' ') + ".partial$ext"
+        }
+        val dot = safeName.lastIndexOf('.')
+        if (dot > 0 && dot < safeName.lastIndex) {
+            return safeName.substring(0, dot).trimEnd('.', ' ') +
+                ".partial" +
+                safeName.substring(dot)
+        }
+        return "$safeName.partial"
+    }
+
+    private fun deleteStaleStagedFiles(parent: DocumentFile, fileName: String, outputExt: String) {
+        val stagedNames = linkedSetOf(
+            buildStagedSafFileName(fileName),
+            buildLegacyStagedSafFileName(fileName, outputExt)
+        )
+        for (stagedName in stagedNames) {
+            try {
+                parent.findFile(stagedName)?.delete()
+            } catch (_: Exception) {
+            }
+        }
+    }
+
+    private fun sanitizeFilename(name: String): String {
+        var sanitized = name
+            .replace("/", " ")
+            .replace(Regex("[\\\\:*?\"<>|]"), " ")
+            .filter { ch ->
+                val code = ch.code
+                !((code < 0x20 && ch != '\t' && ch != '\n' && ch != '\r') ||
+                    code == 0x7F ||
+                    (Character.isISOControl(ch) && ch != '\t' && ch != '\n' && ch != '\r'))
+            }
+            .trim()
+            .trim('.', ' ')
+
+        sanitized = sanitized
+            .replace(Regex("\\s+"), " ")
+            .replace(Regex("_+"), "_")
+            .trim('_', ' ')
+
+        sanitized = truncateSafDisplayName(sanitized, MAX_SAF_DISPLAY_NAME_UTF8_BYTES)
+        sanitized = sanitized.trim().trim('.', ' ').trim('_', ' ')
+        return if (sanitized.isBlank()) "Unknown" else sanitized
+    }
+
+    private fun truncateSafDisplayName(name: String, maxBytes: Int): String {
+        if (maxBytes <= 0 || name.toByteArray(Charsets.UTF_8).size <= maxBytes) return name
+
+        val dotIndex = name.lastIndexOf('.')
+        val ext = if (
+            dotIndex > 0 &&
+            dotIndex < name.length - 1 &&
+            name.length - dotIndex <= 10
+        ) {
+            name.substring(dotIndex)
+        } else {
+            ""
+        }
+        val stem = if (ext.isNotEmpty()) name.substring(0, dotIndex) else name
+        val maxStemBytes = (maxBytes - ext.toByteArray(Charsets.UTF_8).size).coerceAtLeast(1)
+        return truncateUtf8Bytes(stem, maxStemBytes).trim().trim('.', ' ').trim('_', ' ') + ext
+    }
+
+    private fun truncateUtf8Bytes(value: String, maxBytes: Int): String {
+        if (maxBytes <= 0 || value.toByteArray(Charsets.UTF_8).size <= maxBytes) return value
+
+        val builder = StringBuilder()
+        var usedBytes = 0
+        var index = 0
+        while (index < value.length) {
+            val codePoint = value.codePointAt(index)
+            val char = String(Character.toChars(codePoint))
+            val charBytes = char.toByteArray(Charsets.UTF_8).size
+            if (usedBytes + charBytes > maxBytes) break
+            builder.append(char)
+            usedBytes += charBytes
+            index += Character.charCount(codePoint)
+        }
+        return builder.toString()
+    }
+
+    private fun sanitizeRelativeDir(relativeDir: String): String {
+        if (relativeDir.isBlank()) return ""
+        return relativeDir
+            .split("/")
+            .map { sanitizeFilename(it) }
+            .filter { it.isNotBlank() && it != "." && it != ".." }
+            .joinToString("/")
+    }
+
+    private fun ensureDocumentDir(
+        context: Context,
+        treeUri: Uri,
+        relativeDir: String
+    ): DocumentFile? {
+        val safeRelativeDir = sanitizeRelativeDir(relativeDir)
+        if (safeRelativeDir.isBlank()) {
+            return DocumentFile.fromTreeUri(context, treeUri)
+        }
+
+        synchronized(safDirLock) {
+            var current = DocumentFile.fromTreeUri(context, treeUri) ?: return null
+            val parts = safeRelativeDir.split("/").filter { it.isNotBlank() }
+            for (part in parts) {
+                val existing = current.findFile(part)
+                current = if (existing != null && existing.isDirectory) {
+                    existing
+                } else {
+                    val created = current.createDirectory(part) ?: return null
+                    val createdName = created.name ?: part
+                    if (createdName != part) {
+                        created.delete()
+                        current.findFile(part) ?: return null
+                    } else {
+                        created
+                    }
+                }
+            }
+            return current
+        }
+    }
+
+    private fun findDocumentDir(
+        context: Context,
+        treeUri: Uri,
+        relativeDir: String
+    ): DocumentFile? {
+        var current = DocumentFile.fromTreeUri(context, treeUri) ?: return null
+        val safeRelativeDir = sanitizeRelativeDir(relativeDir)
+        if (safeRelativeDir.isBlank()) return current
+
+        val parts = safeRelativeDir.split("/").filter { it.isNotBlank() }
+        for (part in parts) {
+            val existing = current.findFile(part)
+            if (existing == null || !existing.isDirectory) return null
+            current = existing
+        }
+        return current
+    }
+
+    private fun createOrReuseDocumentFile(
+        parent: DocumentFile,
+        mimeType: String,
+        fileName: String
+    ): DocumentFile? {
+        val safeFileName = sanitizeFilename(fileName)
+        if (safeFileName.isBlank()) return null
+
+        synchronized(safDirLock) {
+            val existing = parent.findFile(safeFileName)
+            if (existing != null && existing.isFile) {
+                return existing
+            }
+
+            val created = parent.createFile(mimeType, safeFileName) ?: return null
+            val createdName = created.name ?: safeFileName
+            if (createdName == safeFileName) {
+                return created
+            }
+
+            val winner = parent.findFile(safeFileName)
+            if (winner != null && winner.isFile) {
+                if (winner.uri != created.uri) {
+                    try {
+                        created.delete()
+                    } catch (_: Exception) {
+                    }
+                }
+                return winner
+            }
+
+            return created
+        }
+    }
+
+    private fun buildSafFileName(req: JSONObject, outputExt: String): String {
+        val provided = req.optString("saf_file_name", "")
+        if (provided.isNotBlank()) return forceFilenameExt(provided, outputExt)
+
+        val trackName = req.optString("track_name", "track")
+        val artistName = req.optString("artist_name", "")
+        val baseName = if (artistName.isNotBlank()) "$artistName - $trackName" else trackName
+        return forceFilenameExt(baseName, outputExt)
+    }
+
+    private fun errorJson(message: String): String {
+        val obj = JSONObject()
+        obj.put("success", false)
+        obj.put("error", message)
+        obj.put("message", message)
+        return obj.toString()
+    }
+}
@@ -1,12 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
-<!-- Modify this file to customize your launch splash screen -->
 <layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="?android:colorBackground" />
-
-    <!-- You can insert your own image assets here -->
-    <!-- <item>
-        <bitmap
-            android:gravity="center"
-            android:src="@mipmap/launch_image" />
-    </item> -->
 </layer-list>
@@ -1,12 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
-<!-- Modify this file to customize your launch splash screen -->
 <layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@android:color/white" />
-
-    <!-- You can insert your own image assets here -->
-    <!-- <item>
-        <bitmap
-            android:gravity="center"
-            android:src="@mipmap/launch_image" />
-    </item> -->
 </layer-list>
@@ -6,4 +6,9 @@
          android:drawable="@drawable/ic_launcher_foreground"
          android:inset="16%" />
  </foreground>
+  <monochrome>
+      <inset
+          android:drawable="@drawable/ic_launcher_monochrome"
+          android:inset="16%" />
+  </monochrome>
 </adaptive-icon>
@@ -1,17 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is on -->
    <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
-        <!-- Show a splash screen on the activity. Automatically removed when
-             the Flutter engine draws its first frame -->
        <item name="android:windowBackground">@drawable/launch_background</item>
    </style>
-    <!-- Theme applied to the Android Window as soon as the process has started.
-         This theme determines the color of the Android Window while your
-         Flutter UI initializes, as well as behind your Flutter UI while its
-         running.
-
-         This Theme is only used starting with V2 of Flutter's Android embedding. -->
    <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
        <item name="android:windowBackground">?android:colorBackground</item>
    </style>
@@ -1,17 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is off -->
    <style name="LaunchTheme" parent="@android:style/Theme.Light.NoTitleBar">
-        <!-- Show a splash screen on the activity. Automatically removed when
-             the Flutter engine draws its first frame -->
        <item name="android:windowBackground">@drawable/launch_background</item>
    </style>
-    <!-- Theme applied to the Android Window as soon as the process has started.
-         This theme determines the color of the Android Window while your
-         Flutter UI initializes, as well as behind your Flutter UI while its
-         running.
-
-         This Theme is only used starting with V2 of Flutter's Android embedding. -->
    <style name="NormalTheme" parent="@android:style/Theme.Light.NoTitleBar">
        <item name="android:windowBackground">?android:colorBackground</item>
    </style>
@@ -1,2 +1,6 @@
-org.gradle.jvmargs=-Xmx4G -XX:MaxMetaspaceSize=2G -XX:ReservedCodeCacheSize=256m -XX:+HeapDumpOnOutOfMemoryError
+org.gradle.jvmargs=-Xmx2g -XX:MaxMetaspaceSize=512m -XX:ReservedCodeCacheSize=256m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
+# This builtInKotlin flag was added automatically by Flutter migrator
+android.builtInKotlin=false
+# This newDsl flag was added automatically by Flutter migrator
+android.newDsl=false
@@ -1,5 +1,9 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.5.0-all.zip
+networkTimeout=10000
+retries=0
+retryBackOffMs=500
+validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-9.3.1-all.zip
@@ -19,8 +19,8 @@ pluginManagement {

 plugins {
    id("dev.flutter.flutter-plugin-loader") version "1.0.0"
-    id("com.android.application") version "8.13.2" apply false
-    id("org.jetbrains.kotlin.android") version "2.2.21" apply false
+    id("com.android.application") version "9.2.1" apply false
+    id("org.jetbrains.kotlin.android") version "2.3.21" apply false
 }

 include(":app")
@@ -1,18 +1,18 @@
 {
-  "name": "SpotiFLAC Source",
+  "name": "SpotiFLAC Mobile Source",
  "identifier": "com.zarzet.spotiflac.source",
  "subtitle": "FLAC Downloader for iOS",
  "apps": [
    {
-      "name": "SpotiFLAC",
+      "name": "SpotiFLAC Mobile",
      "bundleIdentifier": "com.zarzet.spotiflac",
      "developerName": "zarzet",
-      "version": "3.9.0",
-      "versionDate": "2026-03-25",
-      "downloadURL": "https://github.com/zarzet/SpotiFLAC-Mobile/releases/download/v3.9.0/SpotiFLAC-v3.9.0-ios-unsigned.ipa",
-      "localizedDescription": "Mobile version of SpotiFLAC written in Flutter. Download Tracks in true FLAC from Tidal, Qobuz, & Amazon Music.",
+      "version": "4.6.0",
+      "versionDate": "2026-06-13",
+      "downloadURL": "https://github.com/zarzet/SpotiFLAC-Mobile/releases/download/v4.6.0/SpotiFLAC-v4.6.0-ios-unsigned.ipa",
+      "localizedDescription": "SpotiFLAC Mobile is written in Flutter. Download tracks in true FLAC from Tidal, Qobuz, & Amazon Music.",
      "iconURL": "https://raw.githubusercontent.com/zarzet/SpotiFLAC-Mobile/main/assets/images/logo.png",
-      "size": 34477323
+      "size": 34347687
    }
  ]
 }
@@ -3,17 +3,21 @@ files:
    translation: /lib/l10n/arb/app_%locale%.arb
    languages_mapping:
      locale:
-        # Short codes for single-variant languages
+        # Keys MUST be the project's Crowdin language ids; values are the
+        # %locale% suffix used in app_%locale%.arb (underscores so Flutter
+        # gen-l10n parses them — hyphenated filenames break gen-l10n).
+        ar: ar
        de: de
-        es: es
+        es-ES: es_ES
        fr: fr
        hi: hi
        id: id
        ja: ja
        ko: ko
        nl: nl
-        pt: pt
+        pt-PT: pt_PT
        ru: ru
-        # Full codes for Chinese variants
+        tr: tr
+        uk: uk
        zh-CN: zh_CN
        zh-TW: zh_TW
@@ -0,0 +1,607 @@
+package gobackend
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+// APEv2 tag format constants.
+const (
+	apeTagPreamble     = "APETAGEX"
+	apeTagHeaderSize   = 32
+	apeTagVersion2     = 2000
+	apeTagFlagHeader   = 1 << 29 // bit 29: this is the header, not the footer
+	apeTagFlagReadOnly = 1 << 0
+	// Item flags: bits 1-2 encode content type
+	apeItemFlagUTF8   = 0 << 1 // 00: UTF-8 text
+	apeItemFlagBinary = 1 << 1 // 01: binary data
+	apeItemFlagLink   = 2 << 1 // 10: external link
+)
+
+// APETagItem represents a single key-value item in an APEv2 tag.
+type APETagItem struct {
+	Key   string
+	Value string
+	Flags uint32
+}
+
+// APETag represents a complete APEv2 tag block.
+type APETag struct {
+	Version  uint32
+	Items    []APETagItem
+	ReadOnly bool
+}
+
+// ReadAPETags reads APEv2 tags from a file.
+// APEv2 tags are typically appended at the end of the file.
+// The layout is: [audio data] [APEv2 header (optional)] [items...] [APEv2 footer]
+// We locate the footer first (last 32 bytes), then read the tag block.
+func ReadAPETags(filePath string) (*APETag, error) {
+	f, err := os.Open(filePath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open file: %w", err)
+	}
+	defer f.Close()
+
+	fi, err := f.Stat()
+	if err != nil {
+		return nil, fmt.Errorf("failed to stat file: %w", err)
+	}
+	fileSize := fi.Size()
+
+	if fileSize < apeTagHeaderSize {
+		return nil, fmt.Errorf("file too small for APE tag")
+	}
+
+	// The footer is the last 32 bytes before any ID3v1 tag (128 bytes).
+	tag, err := readAPETagAtOffset(f, fileSize, fileSize-apeTagHeaderSize)
+	if err == nil {
+		return tag, nil
+	}
+
+	// Retry: skip ID3v1 tag (128 bytes) if present
+	if fileSize > apeTagHeaderSize+128 {
+		tag, err = readAPETagAtOffset(f, fileSize, fileSize-apeTagHeaderSize-128)
+		if err == nil {
+			return tag, nil
+		}
+	}
+
+	return nil, fmt.Errorf("no APEv2 tag found")
+}
+
+func readAPETagAtOffset(f *os.File, fileSize, footerOffset int64) (*APETag, error) {
+	if footerOffset < 0 || footerOffset+apeTagHeaderSize > fileSize {
+		return nil, fmt.Errorf("invalid footer offset")
+	}
+
+	footer := make([]byte, apeTagHeaderSize)
+	if _, err := f.ReadAt(footer, footerOffset); err != nil {
+		return nil, fmt.Errorf("failed to read APE footer: %w", err)
+	}
+
+	if string(footer[0:8]) != apeTagPreamble {
+		return nil, fmt.Errorf("APE preamble not found")
+	}
+
+	version := binary.LittleEndian.Uint32(footer[8:12])
+	tagSize := binary.LittleEndian.Uint32(footer[12:16]) // size of items + footer (32 bytes)
+	itemCount := binary.LittleEndian.Uint32(footer[16:20])
+	flags := binary.LittleEndian.Uint32(footer[20:24])
+
+	if version != apeTagVersion2 && version != 1000 {
+		return nil, fmt.Errorf("unsupported APE tag version: %d", version)
+	}
+	if tagSize < apeTagHeaderSize {
+		return nil, fmt.Errorf("APE tag size too small: %d", tagSize)
+	}
+	if itemCount > 1000 {
+		return nil, fmt.Errorf("APE tag item count too large: %d", itemCount)
+	}
+
+	// This should be the footer (bit 29 clear)
+	isHeader := (flags & apeTagFlagHeader) != 0
+	if isHeader {
+		return nil, fmt.Errorf("expected APE footer but found header")
+	}
+
+	// tagSize includes items + footer (32 bytes), but NOT the header.
+	itemsSize := int64(tagSize) - apeTagHeaderSize
+	if itemsSize < 0 {
+		return nil, fmt.Errorf("invalid APE tag: items size negative")
+	}
+
+	itemsOffset := footerOffset - itemsSize
+	if itemsOffset < 0 {
+		return nil, fmt.Errorf("APE tag items extend before file start")
+	}
+
+	itemsData := make([]byte, itemsSize)
+	if _, err := f.ReadAt(itemsData, itemsOffset); err != nil {
+		return nil, fmt.Errorf("failed to read APE items: %w", err)
+	}
+
+	items, err := parseAPEItems(itemsData, int(itemCount))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse APE items: %w", err)
+	}
+
+	return &APETag{
+		Version:  version,
+		Items:    items,
+		ReadOnly: (flags & apeTagFlagReadOnly) != 0,
+	}, nil
+}
+
+func parseAPEItems(data []byte, count int) ([]APETagItem, error) {
+	items := make([]APETagItem, 0, count)
+	pos := 0
+
+	for i := 0; i < count && pos < len(data); i++ {
+		if pos+8 > len(data) {
+			break
+		}
+
+		valueSize := int(binary.LittleEndian.Uint32(data[pos : pos+4]))
+		itemFlags := binary.LittleEndian.Uint32(data[pos+4 : pos+8])
+		pos += 8
+
+		// Key is null-terminated ASCII (2-255 bytes, case-insensitive)
+		keyEnd := pos
+		for keyEnd < len(data) && data[keyEnd] != 0 {
+			keyEnd++
+		}
+		if keyEnd >= len(data) {
+			break
+		}
+
+		key := string(data[pos:keyEnd])
+		pos = keyEnd + 1
+
+		if pos+valueSize > len(data) {
+			break
+		}
+		value := string(data[pos : pos+valueSize])
+		pos += valueSize
+
+		items = append(items, APETagItem{
+			Key:   key,
+			Value: value,
+			Flags: itemFlags,
+		})
+	}
+
+	return items, nil
+}
+
+// WriteAPETags writes APEv2 tags to the end of a file.
+// If the file already has APEv2 tags, they are replaced.
+// The tag is written with both header and footer.
+func WriteAPETags(filePath string, tag *APETag) error {
+	existingSize, err := findExistingAPETagSize(filePath)
+	if err != nil {
+		return fmt.Errorf("failed to check existing APE tag: %w", err)
+	}
+
+	tagData, err := marshalAPETag(tag)
+	if err != nil {
+		return fmt.Errorf("failed to marshal APE tag: %w", err)
+	}
+
+	if existingSize > 0 {
+		fi, err := os.Stat(filePath)
+		if err != nil {
+			return fmt.Errorf("failed to stat file: %w", err)
+		}
+		newSize := fi.Size() - int64(existingSize)
+		if err := os.Truncate(filePath, newSize); err != nil {
+			return fmt.Errorf("failed to truncate existing APE tag: %w", err)
+		}
+	}
+
+	f, err := os.OpenFile(filePath, os.O_WRONLY|os.O_APPEND, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to open file for writing: %w", err)
+	}
+	defer f.Close()
+
+	if _, err := f.Write(tagData); err != nil {
+		return fmt.Errorf("failed to write APE tag: %w", err)
+	}
+
+	return nil
+}
+
+// findExistingAPETagSize returns the total size of an existing APE tag
+// (header + items + footer) at the end of the file, or 0 if none exists.
+func findExistingAPETagSize(filePath string) (int64, error) {
+	f, err := os.Open(filePath)
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+
+	fi, err := f.Stat()
+	if err != nil {
+		return 0, err
+	}
+	fileSize := fi.Size()
+
+	offsets := []int64{fileSize - apeTagHeaderSize}
+	if fileSize > apeTagHeaderSize+128 {
+		offsets = append(offsets, fileSize-apeTagHeaderSize-128)
+	}
+
+	for _, offset := range offsets {
+		if offset < 0 {
+			continue
+		}
+		footer := make([]byte, apeTagHeaderSize)
+		if _, err := f.ReadAt(footer, offset); err != nil {
+			continue
+		}
+		if string(footer[0:8]) != apeTagPreamble {
+			continue
+		}
+
+		flags := binary.LittleEndian.Uint32(footer[20:24])
+		if (flags & apeTagFlagHeader) != 0 {
+			continue
+		}
+
+		tagSize := int64(binary.LittleEndian.Uint32(footer[12:16]))
+
+		hasHeader := (flags & (1 << 31)) != 0 // bit 31 = tag contains header
+		totalSize := tagSize
+		if hasHeader {
+			totalSize += apeTagHeaderSize
+		}
+
+		// Include any trailing data after the footer (e.g. ID3v1 128-byte tag).
+		// When truncating, we must remove the APE tag AND everything after it.
+		trailingBytes := fileSize - (offset + apeTagHeaderSize)
+		totalSize += trailingBytes
+
+		return totalSize, nil
+	}
+
+	return 0, nil
+}
+
+// marshalAPETag serializes an APETag into bytes (header + items + footer).
+func marshalAPETag(tag *APETag) ([]byte, error) {
+	if tag == nil || len(tag.Items) == 0 {
+		return nil, fmt.Errorf("empty APE tag")
+	}
+
+	var itemsData []byte
+	for _, item := range tag.Items {
+		keyBytes := []byte(item.Key)
+		valueBytes := []byte(item.Value)
+
+		// 4 bytes: value size (LE)
+		sizeBuf := make([]byte, 4)
+		binary.LittleEndian.PutUint32(sizeBuf, uint32(len(valueBytes)))
+
+		// 4 bytes: item flags (LE)
+		flagsBuf := make([]byte, 4)
+		binary.LittleEndian.PutUint32(flagsBuf, item.Flags)
+
+		itemsData = append(itemsData, sizeBuf...)
+		itemsData = append(itemsData, flagsBuf...)
+		itemsData = append(itemsData, keyBytes...)
+		itemsData = append(itemsData, 0)
+		itemsData = append(itemsData, valueBytes...)
+	}
+
+	// tagSize = items data + footer (32 bytes)
+	tagSize := uint32(len(itemsData) + apeTagHeaderSize)
+	itemCount := uint32(len(tag.Items))
+
+	version := uint32(apeTagVersion2)
+	if tag.Version != 0 {
+		version = tag.Version
+	}
+
+	// flags: bit 29 = 1 (is header), bit 31 = 1 (contains header)
+	headerFlags := uint32(apeTagFlagHeader | (1 << 31))
+	header := buildAPEHeaderFooter(version, tagSize, itemCount, headerFlags)
+
+	// flags: bit 29 = 0 (is footer), bit 31 = 1 (contains header)
+	footerFlags := uint32(1 << 31)
+	footer := buildAPEHeaderFooter(version, tagSize, itemCount, footerFlags)
+
+	// Final layout: header + items + footer
+	result := make([]byte, 0, len(header)+len(itemsData)+len(footer))
+	result = append(result, header...)
+	result = append(result, itemsData...)
+	result = append(result, footer...)
+
+	return result, nil
+}
+
+func buildAPEHeaderFooter(version, tagSize, itemCount, flags uint32) []byte {
+	buf := make([]byte, apeTagHeaderSize)
+	copy(buf[0:8], apeTagPreamble)
+	binary.LittleEndian.PutUint32(buf[8:12], version)
+	binary.LittleEndian.PutUint32(buf[12:16], tagSize)
+	binary.LittleEndian.PutUint32(buf[16:20], itemCount)
+	binary.LittleEndian.PutUint32(buf[20:24], flags)
+	// bytes 24-31 are reserved (zeros)
+	return buf
+}
+
+// APETagToAudioMetadata converts an APETag to our unified AudioMetadata struct.
+func APETagToAudioMetadata(tag *APETag) *AudioMetadata {
+	if tag == nil {
+		return nil
+	}
+
+	metadata := &AudioMetadata{}
+	for _, item := range tag.Items {
+		key := strings.ToUpper(strings.TrimSpace(item.Key))
+		value := strings.TrimSpace(item.Value)
+		if value == "" {
+			continue
+		}
+
+		switch key {
+		case "TITLE":
+			metadata.Title = value
+		case "ARTIST":
+			metadata.Artist = value
+		case "ALBUM":
+			metadata.Album = value
+		case "ALBUMARTIST", "ALBUM ARTIST":
+			metadata.AlbumArtist = value
+		case "GENRE":
+			metadata.Genre = value
+		case "YEAR":
+			metadata.Year = value
+		case "DATE":
+			metadata.Date = value
+		case "TRACK", "TRACKNUMBER":
+			metadata.TrackNumber, metadata.TotalTracks = parseIndexPair(value)
+		case "DISC", "DISCNUMBER":
+			metadata.DiscNumber, metadata.TotalDiscs = parseIndexPair(value)
+		case "ISRC":
+			metadata.ISRC = value
+		case "LYRICS", "UNSYNCEDLYRICS":
+			if metadata.Lyrics == "" {
+				metadata.Lyrics = value
+			}
+		case "LABEL", "PUBLISHER":
+			metadata.Label = value
+		case "COPYRIGHT":
+			metadata.Copyright = value
+		case "COMPOSER":
+			metadata.Composer = value
+		case "COMMENT":
+			metadata.Comment = value
+		case "REPLAYGAIN_TRACK_GAIN":
+			metadata.ReplayGainTrackGain = value
+		case "REPLAYGAIN_TRACK_PEAK":
+			metadata.ReplayGainTrackPeak = value
+		case "REPLAYGAIN_ALBUM_GAIN":
+			metadata.ReplayGainAlbumGain = value
+		case "REPLAYGAIN_ALBUM_PEAK":
+			metadata.ReplayGainAlbumPeak = value
+		}
+	}
+
+	return metadata
+}
+
+// AudioMetadataToAPEItems converts metadata fields to APE tag items.
+func AudioMetadataToAPEItems(metadata *AudioMetadata) []APETagItem {
+	if metadata == nil {
+		return nil
+	}
+
+	var items []APETagItem
+	addItem := func(key, value string) {
+		if value != "" {
+			items = append(items, APETagItem{Key: key, Value: value})
+		}
+	}
+
+	addItem("Title", metadata.Title)
+	addItem("Artist", metadata.Artist)
+	addItem("Album", metadata.Album)
+	addItem("Album Artist", metadata.AlbumArtist)
+	addItem("Genre", metadata.Genre)
+	if metadata.Date != "" {
+		addItem("Year", metadata.Date)
+	} else if metadata.Year != "" {
+		addItem("Year", metadata.Year)
+	}
+	if metadata.TrackNumber > 0 {
+		addItem("Track", formatIndexValue(metadata.TrackNumber, metadata.TotalTracks))
+	}
+	if metadata.DiscNumber > 0 {
+		addItem("Disc", formatIndexValue(metadata.DiscNumber, metadata.TotalDiscs))
+	}
+	addItem("ISRC", metadata.ISRC)
+	addItem("Lyrics", metadata.Lyrics)
+	addItem("Label", metadata.Label)
+	addItem("Copyright", metadata.Copyright)
+	addItem("Composer", metadata.Composer)
+	addItem("Comment", metadata.Comment)
+	addItem("REPLAYGAIN_TRACK_GAIN", metadata.ReplayGainTrackGain)
+	addItem("REPLAYGAIN_TRACK_PEAK", metadata.ReplayGainTrackPeak)
+	addItem("REPLAYGAIN_ALBUM_GAIN", metadata.ReplayGainAlbumGain)
+	addItem("REPLAYGAIN_ALBUM_PEAK", metadata.ReplayGainAlbumPeak)
+
+	return items
+}
+
+// apeKeysFromFields builds a set of upper-case APE tag keys corresponding to
+// the metadata fields map sent by the editor.  This is used during merge to
+// ensure that even empty (cleared) fields override old values.
+func apeKeysFromFields(fields map[string]string) map[string]struct{} {
+	mapping := map[string]string{
+		"title":                 "TITLE",
+		"artist":                "ARTIST",
+		"album":                 "ALBUM",
+		"album_artist":          "ALBUM ARTIST",
+		"date":                  "DATE",
+		"genre":                 "GENRE",
+		"track_number":          "TRACK",
+		"disc_number":           "DISC",
+		"isrc":                  "ISRC",
+		"lyrics":                "LYRICS",
+		"label":                 "LABEL",
+		"copyright":             "COPYRIGHT",
+		"composer":              "COMPOSER",
+		"comment":               "COMMENT",
+		"replaygain_track_gain": "REPLAYGAIN_TRACK_GAIN",
+		"replaygain_track_peak": "REPLAYGAIN_TRACK_PEAK",
+		"replaygain_album_gain": "REPLAYGAIN_ALBUM_GAIN",
+		"replaygain_album_peak": "REPLAYGAIN_ALBUM_PEAK",
+	}
+	result := make(map[string]struct{})
+	for fk, apeKey := range mapping {
+		if _, present := fields[fk]; present {
+			result[strings.ToUpper(apeKey)] = struct{}{}
+		}
+	}
+	// Some fields have reader aliases that must also be cleared when the
+	// canonical key is updated (e.g. DATE writer ↔ DATE/YEAR reader,
+	// DISC ↔ DISCNUMBER, TRACK ↔ TRACKNUMBER, "ALBUM ARTIST" ↔ ALBUMARTIST,
+	// LABEL ↔ PUBLISHER, LYRICS ↔ UNSYNCEDLYRICS).
+	if _, present := fields["date"]; present {
+		result["DATE"] = struct{}{}
+	}
+	if _, present := fields["disc_number"]; present {
+		result["DISCNUMBER"] = struct{}{}
+	}
+	if _, present := fields["disc_total"]; present {
+		result["DISCNUMBER"] = struct{}{}
+	}
+	if _, present := fields["track_number"]; present {
+		result["TRACKNUMBER"] = struct{}{}
+	}
+	if _, present := fields["track_total"]; present {
+		result["TRACKNUMBER"] = struct{}{}
+	}
+	if _, present := fields["album_artist"]; present {
+		result["ALBUMARTIST"] = struct{}{}
+	}
+	if _, present := fields["label"]; present {
+		result["PUBLISHER"] = struct{}{}
+	}
+	if _, present := fields["lyrics"]; present {
+		result["UNSYNCEDLYRICS"] = struct{}{}
+	}
+	return result
+}
+
+// MergeAPEItems overlays newItems on top of existing items.
+// For each new item, if a matching key exists (case-insensitive) in existing,
+// it is replaced. New keys are appended. Existing items whose keys are NOT
+// in newItems are preserved (cover art, ReplayGain, custom tags, etc.).
+//
+// overrideKeys is an optional set of upper-case keys that should be removed
+// from existing even if they do not appear in newItems.  This handles field
+// deletion: the caller sends an empty value which is not serialized into
+// newItems, but the old value must still be dropped.
+func MergeAPEItems(existing, newItems []APETagItem, overrideKeys map[string]struct{}) []APETagItem {
+	combined := make(map[string]struct{}, len(newItems)+len(overrideKeys))
+	for k := range overrideKeys {
+		combined[strings.ToUpper(k)] = struct{}{}
+	}
+	for _, item := range newItems {
+		combined[strings.ToUpper(item.Key)] = struct{}{}
+	}
+
+	var merged []APETagItem
+	for _, item := range existing {
+		if _, overwritten := combined[strings.ToUpper(item.Key)]; !overwritten {
+			merged = append(merged, item)
+		}
+	}
+
+	merged = append(merged, newItems...)
+
+	return merged
+}
+
+// ReadAPETagsFromReader reads APEv2 tags from an io.ReaderAt + size.
+// This is useful for reading APE tags from files opened via SAF or other abstractions.
+func ReadAPETagsFromReader(r io.ReaderAt, fileSize int64) (*APETag, error) {
+	if fileSize < apeTagHeaderSize {
+		return nil, fmt.Errorf("file too small for APE tag")
+	}
+
+	footer := make([]byte, apeTagHeaderSize)
+	if _, err := r.ReadAt(footer, fileSize-apeTagHeaderSize); err != nil {
+		return nil, fmt.Errorf("failed to read APE footer: %w", err)
+	}
+
+	if string(footer[0:8]) == apeTagPreamble {
+		tag, err := parseAPETagFromFooter(r, fileSize, fileSize-apeTagHeaderSize, footer)
+		if err == nil {
+			return tag, nil
+		}
+	}
+
+	// Retry: skip ID3v1 tag (128 bytes)
+	if fileSize > apeTagHeaderSize+128 {
+		offset := fileSize - apeTagHeaderSize - 128
+		if _, err := r.ReadAt(footer, offset); err == nil {
+			if string(footer[0:8]) == apeTagPreamble {
+				tag, err := parseAPETagFromFooter(r, fileSize, offset, footer)
+				if err == nil {
+					return tag, nil
+				}
+			}
+		}
+	}
+
+	return nil, fmt.Errorf("no APEv2 tag found")
+}
+
+func parseAPETagFromFooter(r io.ReaderAt, fileSize, footerOffset int64, footer []byte) (*APETag, error) {
+	version := binary.LittleEndian.Uint32(footer[8:12])
+	tagSize := binary.LittleEndian.Uint32(footer[12:16])
+	itemCount := binary.LittleEndian.Uint32(footer[16:20])
+	flags := binary.LittleEndian.Uint32(footer[20:24])
+
+	if version != apeTagVersion2 && version != 1000 {
+		return nil, fmt.Errorf("unsupported APE tag version: %d", version)
+	}
+	if tagSize < apeTagHeaderSize {
+		return nil, fmt.Errorf("APE tag size too small: %d", tagSize)
+	}
+	if itemCount > 1000 {
+		return nil, fmt.Errorf("APE tag item count too large: %d", itemCount)
+	}
+	if (flags & apeTagFlagHeader) != 0 {
+		return nil, fmt.Errorf("expected footer, found header")
+	}
+
+	itemsSize := int64(tagSize) - apeTagHeaderSize
+	itemsOffset := footerOffset - itemsSize
+	if itemsOffset < 0 {
+		return nil, fmt.Errorf("APE items extend before file start")
+	}
+
+	itemsData := make([]byte, itemsSize)
+	if _, err := r.ReadAt(itemsData, itemsOffset); err != nil {
+		return nil, fmt.Errorf("failed to read APE items: %w", err)
+	}
+
+	items, err := parseAPEItems(itemsData, int(itemCount))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse APE items: %w", err)
+	}
+
+	return &APETag{
+		Version:  version,
+		Items:    items,
+		ReadOnly: (flags & apeTagFlagReadOnly) != 0,
+	}, nil
+}
@@ -0,0 +1,121 @@
+package gobackend
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestAPETagReadWriteMergeAndMetadataConversion(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "sample.ape")
+	if err := os.WriteFile(path, []byte("audio-data"), 0600); err != nil {
+		t.Fatalf("write sample: %v", err)
+	}
+
+	metadata := &AudioMetadata{
+		Title:               "Song",
+		Artist:              "Artist",
+		Album:               "Album",
+		AlbumArtist:         "Album Artist",
+		Genre:               "Pop",
+		Date:                "2026",
+		TrackNumber:         3,
+		TotalTracks:         12,
+		DiscNumber:          1,
+		TotalDiscs:          2,
+		ISRC:                "USRC17607839",
+		Lyrics:              "lyrics",
+		Label:               "Label",
+		Copyright:           "Copyright",
+		Composer:            "Composer",
+		Comment:             "Comment",
+		ReplayGainTrackGain: "-6.50 dB",
+		ReplayGainTrackPeak: "0.98",
+		ReplayGainAlbumGain: "-5.00 dB",
+		ReplayGainAlbumPeak: "0.99",
+	}
+	items := AudioMetadataToAPEItems(metadata)
+	if len(items) == 0 {
+		t.Fatal("expected APE items")
+	}
+
+	tag := &APETag{Items: append(items, APETagItem{Key: "Custom", Value: "Keep"})}
+	if err := WriteAPETags(path, tag); err != nil {
+		t.Fatalf("WriteAPETags: %v", err)
+	}
+
+	readTag, err := ReadAPETags(path)
+	if err != nil {
+		t.Fatalf("ReadAPETags: %v", err)
+	}
+	if readTag.Version != apeTagVersion2 {
+		t.Fatalf("version = %d", readTag.Version)
+	}
+	readMetadata := APETagToAudioMetadata(readTag)
+	if readMetadata.Title != "Song" || readMetadata.TrackNumber != 3 || readMetadata.TotalTracks != 12 {
+		t.Fatalf("metadata = %#v", readMetadata)
+	}
+
+	readerTag, err := ReadAPETagsFromReader(bytes.NewReader(mustReadFile(t, path)), int64(len(mustReadFile(t, path))))
+	if err != nil {
+		t.Fatalf("ReadAPETagsFromReader: %v", err)
+	}
+	if len(readerTag.Items) != len(readTag.Items) {
+		t.Fatalf("reader items = %d, file items = %d", len(readerTag.Items), len(readTag.Items))
+	}
+
+	override := apeKeysFromFields(map[string]string{"title": "", "lyrics": "", "disc_total": ""})
+	merged := MergeAPEItems(readTag.Items, []APETagItem{{Key: "Title", Value: "New Song"}}, override)
+	mergedMeta := APETagToAudioMetadata(&APETag{Items: merged})
+	if mergedMeta.Title != "New Song" {
+		t.Fatalf("merged title = %q", mergedMeta.Title)
+	}
+	if mergedMeta.Lyrics != "" {
+		t.Fatalf("expected lyrics cleared, got %q", mergedMeta.Lyrics)
+	}
+
+	if err := WriteAPETags(path, &APETag{Items: []APETagItem{{Key: "Title", Value: "Replacement"}}}); err != nil {
+		t.Fatalf("replace APE tags: %v", err)
+	}
+	replaced, err := ReadAPETags(path)
+	if err != nil {
+		t.Fatalf("read replacement: %v", err)
+	}
+	if got := APETagToAudioMetadata(replaced).Title; got != "Replacement" {
+		t.Fatalf("replacement title = %q", got)
+	}
+
+	if _, err := marshalAPETag(nil); err == nil {
+		t.Fatal("expected empty tag error")
+	}
+	if _, err := ReadAPETags(filepath.Join(dir, "missing.ape")); err == nil {
+		t.Fatal("expected missing file error")
+	}
+	if _, err := ReadAPETagsFromReader(bytes.NewReader([]byte("short")), 5); err == nil {
+		t.Fatal("expected small reader error")
+	}
+}
+
+func TestAPETagInvalidFooterBranches(t *testing.T) {
+	footer := buildAPEHeaderFooter(9999, apeTagHeaderSize, 1, 0)
+	if _, err := parseAPETagFromFooter(bytes.NewReader(footer), int64(len(footer)), 0, footer); err == nil {
+		t.Fatal("expected unsupported version")
+	}
+
+	footer = buildAPEHeaderFooter(apeTagVersion2, apeTagHeaderSize-1, 1, 0)
+	if _, err := parseAPETagFromFooter(bytes.NewReader(footer), int64(len(footer)), 0, footer); err == nil {
+		t.Fatal("expected small tag size")
+	}
+
+	footer = buildAPEHeaderFooter(apeTagVersion2, apeTagHeaderSize, 1001, 0)
+	if _, err := parseAPETagFromFooter(bytes.NewReader(footer), int64(len(footer)), 0, footer); err == nil {
+		t.Fatal("expected too many items")
+	}
+
+	footer = buildAPEHeaderFooter(apeTagVersion2, apeTagHeaderSize, 1, apeTagFlagHeader)
+	if _, err := parseAPETagFromFooter(bytes.NewReader(footer), int64(len(footer)), 0, footer); err == nil {
+		t.Fatal("expected header flag error")
+	}
+}
@@ -21,13 +21,20 @@ type AudioMetadata struct {
 	Year        string
 	Date        string
 	TrackNumber int
+	TotalTracks int
 	DiscNumber  int
+	TotalDiscs  int
 	ISRC        string
 	Lyrics      string
 	Label       string
 	Copyright   string
 	Composer    string
 	Comment     string
+	// ReplayGain fields (text values, e.g. "-6.50 dB", "0.988831")
+	ReplayGainTrackGain string
+	ReplayGainTrackPeak string
+	ReplayGainAlbumGain string
+	ReplayGainAlbumPeak string
 }

 type MP3Quality struct {
@@ -168,9 +175,9 @@ func parseID3v22Frames(data []byte, metadata *AudioMetadata, tagUnsync bool) {
 		case "TCO":
 			metadata.Genre = cleanGenre(value)
 		case "TRK":
-			metadata.TrackNumber = parseTrackNumber(value)
+			metadata.TrackNumber, metadata.TotalTracks = parseIndexPair(value)
 		case "TPA":
-			metadata.DiscNumber = parseTrackNumber(value)
+			metadata.DiscNumber, metadata.TotalDiscs = parseIndexPair(value)
 		case "TCM":
 			metadata.Composer = value
 		case "TPB":
@@ -287,9 +294,9 @@ func parseID3v23Frames(data []byte, metadata *AudioMetadata, version byte, tagUn
 		case "TCON":
 			metadata.Genre = cleanGenre(value)
 		case "TRCK":
-			metadata.TrackNumber = parseTrackNumber(value)
+			metadata.TrackNumber, metadata.TotalTracks = parseIndexPair(value)
 		case "TPOS":
-			metadata.DiscNumber = parseTrackNumber(value)
+			metadata.DiscNumber, metadata.TotalDiscs = parseIndexPair(value)
 		case "TSRC":
 			metadata.ISRC = value
 		case "TCOM":
@@ -311,6 +318,17 @@ func parseID3v23Frames(data []byte, metadata *AudioMetadata, version byte, tagUn
 			if isLyricsDescription(desc) && userValue != "" && metadata.Lyrics == "" {
 				metadata.Lyrics = userValue
 			}
+			upperDesc := strings.ToUpper(desc)
+			switch upperDesc {
+			case "REPLAYGAIN_TRACK_GAIN":
+				metadata.ReplayGainTrackGain = userValue
+			case "REPLAYGAIN_TRACK_PEAK":
+				metadata.ReplayGainTrackPeak = userValue
+			case "REPLAYGAIN_ALBUM_GAIN":
+				metadata.ReplayGainAlbumGain = userValue
+			case "REPLAYGAIN_ALBUM_PEAK":
+				metadata.ReplayGainAlbumPeak = userValue
+			}
 		}

 		pos += 10 + frameSize
@@ -338,7 +356,6 @@ func readID3v1(file *os.File) (*AudioMetadata, error) {
 		Year:   strings.TrimRight(string(tag[93:97]), " \x00"),
 	}

-	// ID3v1.1 track number (if byte 125 is 0 and byte 126 is not)
 	if tag[125] == 0 && tag[126] != 0 {
 		metadata.TrackNumber = int(tag[126])
 	}
@@ -373,27 +390,23 @@ func extractTextFrame(data []byte) string {
 	}
 }

-// extractCommentFrame parses an ID3v2 COMM frame.
-// Format: encoding(1) + language(3) + description(null-terminated) + text
 func extractCommentFrame(data []byte) string {
 	if len(data) < 5 {
 		return ""
 	}
 	encoding := data[0]
-	// skip 3-byte language code
 	rest := data[4:]

-	// find null terminator separating description from text
 	var text []byte
 	switch encoding {
-	case 1, 2: // UTF-16 variants use double-null terminator
+	case 1, 2:
 		for i := 0; i+1 < len(rest); i += 2 {
 			if rest[i] == 0 && rest[i+1] == 0 {
 				text = rest[i+2:]
 				break
 			}
 		}
-	default: // ISO-8859-1 or UTF-8
+	default:
 		idx := bytes.IndexByte(rest, 0)
 		if idx >= 0 && idx+1 < len(rest) {
 			text = rest[idx+1:]
@@ -406,33 +419,30 @@ func extractCommentFrame(data []byte) string {
 		return ""
 	}

-	// re-prepend encoding byte so extractTextFrame can decode properly
 	framed := make([]byte, 1+len(text))
 	framed[0] = encoding
 	copy(framed[1:], text)
 	return extractTextFrame(framed)
 }

-// extractLyricsFrame parses ID3 unsynchronized lyrics frames (USLT/ULT).
-// Format: encoding(1) + language(3) + description(null-terminated) + lyrics text.
 func extractLyricsFrame(data []byte) string {
 	if len(data) < 5 {
 		return ""
 	}

 	encoding := data[0]
-	rest := data[4:] // skip 3-byte language code
+	rest := data[4:]

 	var text []byte
 	switch encoding {
-	case 1, 2: // UTF-16 variants use double-null terminator
+	case 1, 2:
 		for i := 0; i+1 < len(rest); i += 2 {
 			if rest[i] == 0 && rest[i+1] == 0 {
 				text = rest[i+2:]
 				break
 			}
 		}
-	default: // ISO-8859-1 or UTF-8
+	default:
 		idx := bytes.IndexByte(rest, 0)
 		if idx >= 0 && idx+1 < len(rest) {
 			text = rest[idx+1:]
@@ -451,8 +461,6 @@ func extractLyricsFrame(data []byte) string {
 	return extractTextFrame(framed)
 }

-// extractUserTextFrame parses ID3 TXXX/TXX user text frame:
-// encoding(1) + description + separator + value.
 func extractUserTextFrame(data []byte) (string, string) {
 	if len(data) < 2 {
 		return "", ""
@@ -463,7 +471,7 @@ func extractUserTextFrame(data []byte) (string, string) {

 	var descRaw, valueRaw []byte
 	switch encoding {
-	case 1, 2: // UTF-16 variants
+	case 1, 2:
 		for i := 0; i+1 < len(payload); i += 2 {
 			if payload[i] == 0 && payload[i+1] == 0 {
 				descRaw = payload[:i]
@@ -471,7 +479,7 @@ func extractUserTextFrame(data []byte) (string, string) {
 				break
 			}
 		}
-	default: // ISO-8859-1 or UTF-8
+	default:
 		idx := bytes.IndexByte(payload, 0)
 		if idx >= 0 {
 			descRaw = payload[:idx]
@@ -498,7 +506,13 @@ func extractUserTextFrame(data []byte) (string, string) {

 func isLyricsDescription(description string) bool {
 	switch strings.ToLower(strings.TrimSpace(description)) {
-	case "lyrics", "lyric", "unsyncedlyrics", "unsynced lyrics", "lrc":
+	case
+		"lyrics",
+		"lyric",
+		"unsyncedlyrics",
+		"unsynced lyrics",
+		"uslt",
+		"lrc":
 		return true
 	default:
 		return false
@@ -568,14 +582,28 @@ func cleanGenre(genre string) string {
 }

 func parseTrackNumber(s string) int {
-	s = strings.TrimSpace(s)
-	if idx := strings.Index(s, "/"); idx > 0 {
-		s = s[:idx]
-	}
-	num, _ := strconv.Atoi(s)
+	num, _ := parseIndexPair(s)
 	return num
 }

+func parseIndexPair(s string) (int, int) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return 0, 0
+	}
+
+	first := s
+	second := ""
+	if idx := strings.Index(s, "/"); idx > 0 {
+		first = s[:idx]
+		second = s[idx+1:]
+	}
+
+	num, _ := strconv.Atoi(strings.TrimSpace(first))
+	total, _ := strconv.Atoi(strings.TrimSpace(second))
+	return num, total
+}
+
 func removeUnsync(data []byte) []byte {
 	if len(data) == 0 {
 		return data
@@ -659,7 +687,6 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {

 	file.Seek(audioStart, io.SeekStart)

-	// Find first valid MP3 frame sync
 	frameHeader := make([]byte, 4)
 	var frameStart int64 = -1
 	for i := 0; i < 10000; i++ {
@@ -686,8 +713,6 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 	sampleRateIdx := (frameHeader[2] >> 2) & 0x03
 	channelMode := (frameHeader[3] >> 6) & 0x03

-	// Sample rate tables: [version][index]
-	// version: 0=MPEG2.5, 1=reserved, 2=MPEG2, 3=MPEG1
 	sampleRates := [][]int{
 		{11025, 12000, 8000},
 		{0, 0, 0},
@@ -698,15 +723,12 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 		quality.SampleRate = sampleRates[version][sampleRateIdx]
 	}

-	// Bitrate tables for all MPEG versions and layers
-	// MPEG1 Layer III
 	if version == 3 && layer == 1 {
 		bitrates := []int{0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0}
 		if bitrateIdx < 16 {
 			quality.Bitrate = bitrates[bitrateIdx] * 1000
 		}
 	}
-	// MPEG2/2.5 Layer III
 	if (version == 0 || version == 2) && layer == 1 {
 		bitrates := []int{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0}
 		if bitrateIdx < 16 {
@@ -714,14 +736,11 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 		}
 	}

-	// Determine samples per frame for duration calculation
 	samplesPerFrame := 1152 // MPEG1 Layer III
 	if version == 0 || version == 2 {
 		samplesPerFrame = 576 // MPEG2/2.5 Layer III
 	}

-	// Try to read Xing/VBRI header from the first frame for VBR info
-	// Xing header offset depends on MPEG version and channel mode
 	var xingOffset int
 	if version == 3 { // MPEG1
 		if channelMode == 3 { // Mono
@@ -737,7 +756,6 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 		}
 	}

-	// Read enough of the first frame to find Xing/VBRI header
 	xingBuf := make([]byte, 200)
 	file.Seek(frameStart+4, io.SeekStart)
 	n, _ := io.ReadFull(file, xingBuf)
@@ -747,7 +765,6 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 	vbrBytes := int64(0)
 	isVBR := false

-	// Check for Xing/Info header
 	if xingOffset+8 <= n {
 		tag := string(xingBuf[xingOffset : xingOffset+4])
 		if tag == "Xing" || tag == "Info" {
@@ -766,7 +783,6 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 		}
 	}

-	// Check for VBRI header (always at offset 32 from frame start + 4)
 	if !isVBR && 36+26 <= n {
 		if string(xingBuf[32:36]) == "VBRI" {
 			vbrBytes = int64(binary.BigEndian.Uint32(xingBuf[36+6 : 36+10]))
@@ -778,11 +794,9 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 	}

 	if isVBR && vbrFrames > 0 && quality.SampleRate > 0 {
-		// Accurate duration from total frames
 		totalSamples := int64(vbrFrames) * int64(samplesPerFrame)
 		quality.Duration = int(totalSamples / int64(quality.SampleRate))

-		// Accurate average bitrate
 		if vbrBytes > 0 && quality.Duration > 0 {
 			quality.Bitrate = int(vbrBytes * 8 / int64(quality.Duration))
 		} else if quality.Duration > 0 {
@@ -790,7 +804,6 @@ func GetMP3Quality(filePath string) (*MP3Quality, error) {
 			quality.Bitrate = int(audioSize * 8 / int64(quality.Duration))
 		}
 	} else if quality.Bitrate > 0 {
-		// CBR fallback: estimate duration from file size and frame bitrate
 		audioSize := fileSize - audioStart - 128 // subtract possible ID3v1 tag
 		if audioSize > 0 {
 			quality.Duration = int(audioSize * 8 / int64(quality.Bitrate))
@@ -974,8 +987,9 @@ func parseVorbisComments(data []byte, metadata *AudioMetadata) {
 	}

 	reader := bytes.NewReader(data)
+	artistValues := make([]string, 0, 1)
+	albumArtistValues := make([]string, 0, 1)

-	// Read vendor string length
 	var vendorLen uint32
 	if err := binary.Read(reader, binary.LittleEndian, &vendorLen); err != nil {
 		return
@@ -1004,8 +1018,6 @@ func parseVorbisComments(data []byte, metadata *AudioMetadata) {
 		if commentLen > remaining {
 			break
 		}
-		// Large comment entries are typically METADATA_BLOCK_PICTURE.
-		// Skip them so we can continue parsing normal text tags after/before.
 		if commentLen > 512*1024 {
 			reader.Seek(int64(commentLen), io.SeekCurrent)
 			continue
@@ -1028,9 +1040,9 @@ func parseVorbisComments(data []byte, metadata *AudioMetadata) {
 		case "TITLE":
 			metadata.Title = value
 		case "ARTIST":
-			metadata.Artist = value
+			artistValues = append(artistValues, value)
 		case "ALBUMARTIST", "ALBUM_ARTIST", "ALBUM ARTIST":
-			metadata.AlbumArtist = value
+			albumArtistValues = append(albumArtistValues, value)
 		case "ALBUM":
 			metadata.Album = value
 		case "DATE", "YEAR":
@@ -1041,9 +1053,9 @@ func parseVorbisComments(data []byte, metadata *AudioMetadata) {
 		case "GENRE":
 			metadata.Genre = value
 		case "TRACKNUMBER", "TRACK":
-			metadata.TrackNumber = parseTrackNumber(value)
+			metadata.TrackNumber, metadata.TotalTracks = parseIndexPair(value)
 		case "DISCNUMBER", "DISC":
-			metadata.DiscNumber = parseTrackNumber(value)
+			metadata.DiscNumber, metadata.TotalDiscs = parseIndexPair(value)
 		case "ISRC":
 			metadata.ISRC = value
 		case "COMPOSER":
@@ -1058,8 +1070,23 @@ func parseVorbisComments(data []byte, metadata *AudioMetadata) {
 			metadata.Label = value
 		case "COPYRIGHT":
 			metadata.Copyright = value
+		case "REPLAYGAIN_TRACK_GAIN":
+			metadata.ReplayGainTrackGain = value
+		case "REPLAYGAIN_TRACK_PEAK":
+			metadata.ReplayGainTrackPeak = value
+		case "REPLAYGAIN_ALBUM_GAIN":
+			metadata.ReplayGainAlbumGain = value
+		case "REPLAYGAIN_ALBUM_PEAK":
+			metadata.ReplayGainAlbumPeak = value
 		}
 	}
+
+	if len(artistValues) > 0 {
+		metadata.Artist = joinVorbisCommentValues(artistValues)
+	}
+	if len(albumArtistValues) > 0 {
+		metadata.AlbumArtist = joinVorbisCommentValues(albumArtistValues)
+	}
 }

 func GetOggQuality(filePath string) (*OggQuality, error) {
@@ -1108,7 +1135,6 @@ func GetOggQuality(filePath string) (*OggQuality, error) {
 		}
 	}

-	// Read granule position from the last Ogg page for accurate duration
 	stat, err := file.Stat()
 	if err != nil {
 		return quality, nil
@@ -1118,7 +1144,6 @@ func GetOggQuality(filePath string) (*OggQuality, error) {
 	granule := readLastOggGranulePosition(file, fileSize)
 	if granule > 0 {
 		if isOpus {
-			// Opus always uses 48kHz granule position internally
 			totalSamples := granule - int64(preSkip)
 			if totalSamples > 0 {
 				durationSec := float64(totalSamples) / 48000.0
@@ -1136,11 +1161,9 @@ func GetOggQuality(filePath string) (*OggQuality, error) {
 		}
 	}

-	// Fallback bitrate estimate if duration exists but bitrate couldn't be derived.
 	if quality.Bitrate <= 0 && quality.Duration > 0 {
 		quality.Bitrate = int(fileSize * 8 / int64(quality.Duration))
 	}
-	// Guard against obviously invalid values from corrupted/unreliable granule reads.
 	if quality.Duration > 24*60*60 {
 		quality.Duration = 0
 		quality.Bitrate = 0
@@ -1152,10 +1175,7 @@ func GetOggQuality(filePath string) (*OggQuality, error) {
 	return quality, nil
 }

-// readLastOggGranulePosition seeks to the end of the file and scans backwards
-// to find the last Ogg page, then reads its granule position (bytes 6-13).
 func readLastOggGranulePosition(file *os.File, fileSize int64) int64 {
-	// Read the last chunk of the file to find the last OggS sync
 	searchSize := int64(65536)
 	if searchSize > fileSize {
 		searchSize = fileSize
@@ -1179,7 +1199,6 @@ func readLastOggGranulePosition(file *os.File, fileSize int64) int64 {
 		if i+27 > n {
 			continue
 		}
-		// Validate minimal header fields to avoid false positives inside payload bytes.
 		version := buf[i+4]
 		headerType := buf[i+5]
 		if version != 0 || headerType > 0x07 {
@@ -1197,7 +1216,6 @@ func readLastOggGranulePosition(file *os.File, fileSize int64) int64 {
 		if i+headerLen+payloadLen > n {
 			continue
 		}
-		// Granule position is at bytes 6-13 of the Ogg page header (little-endian int64).
 		return int64(binary.LittleEndian.Uint64(buf[i+6 : i+14]))
 	}
 	return 0
@@ -1257,7 +1275,6 @@ func extractMP3CoverArt(filePath string) ([]byte, string, error) {
 		return nil, "", err
 	}

-	// Parse frames looking for APIC (Attached Picture)
 	pos := 0
 	var frameIDLen, headerLen int
 	if majorVersion == 2 {
@@ -1288,7 +1305,6 @@ func extractMP3CoverArt(filePath string) ([]byte, string, error) {
 			break
 		}

-		// Check for APIC (ID3v2.3/2.4) or PIC (ID3v2.2)
 		if (frameIDLen == 4 && frameID == "APIC") || (frameIDLen == 3 && frameID == "PIC") {
 			frameData := tagData[pos+headerLen : pos+headerLen+frameSize]
 			imageData, mimeType := parseAPICFrame(frameData, majorVersion)
@@ -1608,20 +1624,37 @@ func extractAnyCoverArtWithHint(filePath, displayNameHint string) ([]byte, strin
 		}
 		return data, mimeType, nil

+	case ".wav", ".aiff", ".aif", ".aifc":
+		return extractWAVAIFFCover(filePath)
+
 	default:
 		return nil, "", fmt.Errorf("unsupported format: %s", ext)
 	}
 }

 func SaveCoverToCache(filePath, cacheDir string) (string, error) {
-	return SaveCoverToCacheWithHint(filePath, "", cacheDir)
+	return SaveCoverToCacheWithHintAndKey(filePath, "", cacheDir, "")
 }

 func SaveCoverToCacheWithHint(filePath, displayNameHint, cacheDir string) (string, error) {
+	return SaveCoverToCacheWithHintAndKey(filePath, displayNameHint, cacheDir, "")
+}
+
+func resolveLibraryCoverCacheKey(filePath, explicitKey string) string {
+	explicitKey = strings.TrimSpace(explicitKey)
+	if explicitKey != "" {
+		return explicitKey
+	}
+
 	cacheKey := filePath
 	if stat, err := os.Stat(filePath); err == nil {
 		cacheKey = fmt.Sprintf("%s|%d|%d", filePath, stat.Size(), stat.ModTime().UnixNano())
 	}
+	return cacheKey
+}
+
+func SaveCoverToCacheWithHintAndKey(filePath, displayNameHint, cacheDir, coverCacheKey string) (string, error) {
+	cacheKey := resolveLibraryCoverCacheKey(filePath, coverCacheKey)
 	hash := hashString(cacheKey)

 	jpgPath := filepath.Join(cacheDir, fmt.Sprintf("cover_%x.jpg", hash))
@@ -0,0 +1,34 @@
+package gobackend
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestResolveLibraryCoverCacheKeyUsesExplicitKey(t *testing.T) {
+	t.Parallel()
+
+	const explicitKey = "content://media/external/audio/media/42|123456"
+	got := resolveLibraryCoverCacheKey("/tmp/saf_random.flac", explicitKey)
+	if got != explicitKey {
+		t.Fatalf("expected explicit cache key %q, got %q", explicitKey, got)
+	}
+}
+
+func TestResolveLibraryCoverCacheKeyUsesFilePathAndStatWhenNoExplicitKey(t *testing.T) {
+	t.Parallel()
+
+	tempFile, err := os.CreateTemp("", "cover-cache-*.flac")
+	if err != nil {
+		t.Fatalf("CreateTemp failed: %v", err)
+	}
+	tempPath := tempFile.Name()
+	tempFile.Close()
+	defer os.Remove(tempPath)
+
+	got := resolveLibraryCoverCacheKey(tempPath, "")
+	if !strings.HasPrefix(got, tempPath+"|") {
+		t.Fatalf("expected stat-based cache key to start with %q, got %q", tempPath+"|", got)
+	}
+}
@@ -0,0 +1,133 @@
+package gobackend
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func ffmpegCommand(args ...string) *exec.Cmd {
+	if ffmpegPath, err := exec.LookPath("ffmpeg"); err == nil {
+		return exec.Command(ffmpegPath, args...)
+	}
+	return exec.Command("ffmpeg", args...)
+}
+
+func runFFmpegTestCommand(t *testing.T, args ...string) {
+	t.Helper()
+	cmd := ffmpegCommand(args...)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("ffmpeg failed: %v\n%s", err, string(output))
+	}
+}
+
+func TestExtractLyricsReadsMp3AfterCoverEmbed(t *testing.T) {
+	if _, err := exec.LookPath("ffmpeg"); err != nil {
+		t.Skip("ffmpeg not available")
+	}
+
+	tempDir := t.TempDir()
+	sourceFlac := filepath.Join(tempDir, "source.flac")
+	baseMp3 := filepath.Join(tempDir, "base.mp3")
+	finalMp3 := filepath.Join(tempDir, "final.mp3")
+	coverPath := filepath.Join(tempDir, "cover.jpg")
+	lyrics := "[ti:Test Song]\n[ar:Test Artist]\n[00:00.00]Hello from embedded lyrics"
+
+	runFFmpegTestCommand(
+		t,
+		"-y",
+		"-f",
+		"lavfi",
+		"-i",
+		"sine=frequency=440:duration=1",
+		"-c:a",
+		"flac",
+		sourceFlac,
+	)
+
+	runFFmpegTestCommand(
+		t,
+		"-y",
+		"-f",
+		"lavfi",
+		"-i",
+		"color=c=red:s=32x32:d=1",
+		"-frames:v",
+		"1",
+		coverPath,
+	)
+
+	runFFmpegTestCommand(
+		t,
+		"-y",
+		"-i",
+		sourceFlac,
+		"-b:a",
+		"320k",
+		"-metadata",
+		"title=Test Song",
+		"-metadata",
+		"artist=Test Artist",
+		"-metadata",
+		"lyrics="+lyrics,
+		baseMp3,
+	)
+
+	runFFmpegTestCommand(
+		t,
+		"-y",
+		"-i",
+		baseMp3,
+		"-i",
+		coverPath,
+		"-map",
+		"0:a",
+		"-map_metadata",
+		"-1",
+		"-map",
+		"1:0",
+		"-c:v:0",
+		"copy",
+		"-id3v2_version",
+		"3",
+		"-metadata",
+		"title=Test Song",
+		"-metadata",
+		"artist=Test Artist",
+		"-metadata",
+		"lyrics="+lyrics,
+		"-metadata:s:v",
+		"title=Album cover",
+		"-metadata:s:v",
+		"comment=Cover (front)",
+		"-c:a",
+		"copy",
+		finalMp3,
+	)
+
+	meta, err := ReadID3Tags(finalMp3)
+	if err != nil {
+		t.Fatalf("ReadID3Tags failed: %v", err)
+	}
+	if meta == nil {
+		t.Fatalf("ReadID3Tags returned nil metadata")
+	}
+
+	embeddedLyrics, err := ExtractLyrics(finalMp3)
+	if err != nil {
+		t.Fatalf("ExtractLyrics failed: %v (metadata=%+v)", err, meta)
+	}
+	if !strings.Contains(embeddedLyrics, "Hello from embedded lyrics") {
+		t.Fatalf("embedded lyrics missing, got %q (metadata=%+v)", embeddedLyrics, meta)
+	}
+	if !strings.Contains(meta.Lyrics, "Hello from embedded lyrics") {
+		t.Fatalf("ReadID3Tags lyrics missing, got %+v", meta)
+	}
+
+	if _, err := os.Stat(finalMp3); err != nil {
+		t.Fatalf("expected final mp3 to exist: %v", err)
+	}
+}
@@ -0,0 +1,517 @@
+package gobackend
+
+import (
+	"bytes"
+	"encoding/base64"
+	"encoding/binary"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestAudioMetadataID3ParsingBranches(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "tagged.mp3")
+	tag := buildID3v23Tag(
+		id3TextFrame("TIT2", "Title"),
+		id3TextFrame("TPE1", "Artist"),
+		id3TextFrame("TPE2", "Album Artist"),
+		id3TextFrame("TALB", "Album"),
+		id3TextFrame("TDRC", "2026-05-04"),
+		id3TextFrame("TCON", "(13)Pop"),
+		id3TextFrame("TRCK", "4/12"),
+		id3TextFrame("TPOS", "1/2"),
+		id3TextFrame("TSRC", "USRC17607839"),
+		id3TextFrame("TCOM", "Composer"),
+		id3TextFrame("TPUB", "Label"),
+		id3TextFrame("TCOP", "Copyright"),
+		id3CommentFrame("COMM", "Comment"),
+		id3CommentFrame("USLT", "Lyrics"),
+		id3UserTextFrame("TXXX", "REPLAYGAIN_TRACK_GAIN", "-6.50 dB"),
+		id3UserTextFrame("TXXX", "REPLAYGAIN_TRACK_PEAK", "0.98"),
+	)
+	if err := os.WriteFile(path, append(tag, []byte("audio")...), 0600); err != nil {
+		t.Fatalf("write ID3v2: %v", err)
+	}
+
+	meta, err := ReadID3Tags(path)
+	if err != nil {
+		t.Fatalf("ReadID3Tags: %v", err)
+	}
+	if meta.Title != "Title" || meta.TrackNumber != 4 || meta.TotalTracks != 12 || meta.Genre != "Pop" {
+		t.Fatalf("metadata = %#v", meta)
+	}
+	if meta.Comment != "Comment" || meta.Lyrics != "Lyrics" || meta.ReplayGainTrackGain == "" {
+		t.Fatalf("metadata comments/lyrics/replaygain = %#v", meta)
+	}
+
+	id3v1Path := filepath.Join(dir, "id3v1.mp3")
+	if err := os.WriteFile(id3v1Path, append([]byte("audio"), buildID3v1Tag("V1 Title", "V1 Artist", "V1 Album", "1999", 7, 13)...), 0600); err != nil {
+		t.Fatalf("write ID3v1: %v", err)
+	}
+	v1, err := ReadID3Tags(id3v1Path)
+	if err != nil {
+		t.Fatalf("ReadID3Tags v1: %v", err)
+	}
+	if v1.Title != "V1 Title" || v1.Artist != "V1 Artist" || v1.Genre == "" {
+		t.Fatalf("v1 = %#v", v1)
+	}
+
+	v22Path := filepath.Join(dir, "id3v22.mp3")
+	v22 := buildID3v22Tag(
+		id3v22TextFrame("TT2", "V22 Title"),
+		id3v22TextFrame("TP1", "V22 Artist"),
+		id3v22TextFrame("TRK", "2/5"),
+		id3v22CommentFrame("ULT", "V22 Lyrics"),
+	)
+	if err := os.WriteFile(v22Path, append(v22, []byte("audio")...), 0600); err != nil {
+		t.Fatalf("write ID3v2.2: %v", err)
+	}
+	v22Meta, err := ReadID3Tags(v22Path)
+	if err != nil {
+		t.Fatalf("ReadID3Tags v2.2: %v", err)
+	}
+	if v22Meta.Title != "V22 Title" || v22Meta.Artist != "V22 Artist" || v22Meta.Lyrics != "V22 Lyrics" {
+		t.Fatalf("v22 = %#v", v22Meta)
+	}
+
+	if got := decodeUTF16([]byte{0xff, 0xfe, 'H', 0, 'i', 0}); got != "Hi" {
+		t.Fatalf("decodeUTF16 = %q", got)
+	}
+	if got := decodeUTF16BE([]byte{0, 'O', 0, 'K'}); got != "OK" {
+		t.Fatalf("decodeUTF16BE = %q", got)
+	}
+	if n, total := parseIndexPair(" 8 / 10 "); n != 8 || total != 10 {
+		t.Fatalf("parseIndexPair = %d/%d", n, total)
+	}
+	if got := parseTrackNumber("9/11"); got != 9 {
+		t.Fatalf("parseTrackNumber = %d", got)
+	}
+	if got := removeUnsync([]byte{0xff, 0x00, 0xe0}); !bytes.Equal(got, []byte{0xff, 0xe0}) {
+		t.Fatalf("removeUnsync = %#v", got)
+	}
+	if got := extendedHeaderSize([]byte{0, 0, 0, 6, 0, 0, 0, 0, 0, 0}, 3); got != 10 {
+		t.Fatalf("extendedHeaderSize = %d", got)
+	}
+	if got := syncsafeToInt([]byte{0, 0, 2, 0}); got != 256 {
+		t.Fatalf("syncsafe = %d", got)
+	}
+}
+
+func TestAudioMetadataCoverAndQualityHelpers(t *testing.T) {
+	png := []byte{0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 0, 0, 0, 0}
+	if detectCoverMIME("cover.jpg", png) != "image/png" || detectCoverMIME("cover.webp", []byte("RIFFxxxxWEBPdata")) != "image/webp" {
+		t.Fatal("cover MIME detection mismatch")
+	}
+	if _, err := buildPictureBlock("", nil); err == nil {
+		t.Fatal("expected empty picture block error")
+	}
+
+	apic := append([]byte{3}, []byte("image/png\x00")...)
+	apic = append(apic, 3, 0)
+	apic = append(apic, png...)
+	image, mime := parseAPICFrame(apic, 3)
+	if mime != "image/png" || !bytes.Equal(image, png) {
+		t.Fatalf("APIC = %s/%v", mime, image)
+	}
+	pic := append([]byte{0}, []byte("PNG")...)
+	pic = append(pic, 3, 0)
+	pic = append(pic, png...)
+	image, mime = parseAPICFrame(pic, 2)
+	if mime != "image/png" || !bytes.Equal(image, png) {
+		t.Fatalf("PIC = %s/%v", mime, image)
+	}
+
+	frame := make([]byte, 10)
+	copy(frame[:4], "APIC")
+	binary.BigEndian.PutUint32(frame[4:8], uint32(len(apic)))
+	tag := append(frame, apic...)
+	header := []byte{'I', 'D', '3', 3, 0, 0, byte(len(tag) >> 21), byte(len(tag) >> 14), byte(len(tag) >> 7), byte(len(tag))}
+	mp3CoverPath := filepath.Join(t.TempDir(), "cover.mp3")
+	if err := os.WriteFile(mp3CoverPath, append(append(header, tag...), []byte("audio")...), 0600); err != nil {
+		t.Fatal(err)
+	}
+	extracted, extractedMIME, err := extractMP3CoverArt(mp3CoverPath)
+	if err != nil || extractedMIME != "image/png" || !bytes.Equal(extracted, png) {
+		t.Fatalf("extractMP3CoverArt = %s/%v/%v", extractedMIME, extracted, err)
+	}
+
+	var picture bytes.Buffer
+	binary.Write(&picture, binary.BigEndian, uint32(3))
+	binary.Write(&picture, binary.BigEndian, uint32(len("image/png")))
+	picture.WriteString("image/png")
+	binary.Write(&picture, binary.BigEndian, uint32(0))
+	binary.Write(&picture, binary.BigEndian, uint32(1))
+	binary.Write(&picture, binary.BigEndian, uint32(1))
+	binary.Write(&picture, binary.BigEndian, uint32(32))
+	binary.Write(&picture, binary.BigEndian, uint32(0))
+	binary.Write(&picture, binary.BigEndian, uint32(len(png)))
+	picture.Write(png)
+	flacImage, flacMIME := parseFLACPictureBlock(picture.Bytes())
+	if flacMIME != "image/png" || !bytes.Equal(flacImage, png) {
+		t.Fatalf("FLAC picture = %s/%v", flacMIME, flacImage)
+	}
+
+	comment := "METADATA_BLOCK_PICTURE=" + base64.StdEncoding.EncodeToString(picture.Bytes())
+	var vorbis bytes.Buffer
+	binary.Write(&vorbis, binary.LittleEndian, uint32(6))
+	vorbis.WriteString("vendor")
+	binary.Write(&vorbis, binary.LittleEndian, uint32(1))
+	binary.Write(&vorbis, binary.LittleEndian, uint32(len(comment)))
+	vorbis.WriteString(comment)
+	commentImage, commentMIME := extractPictureFromVorbisComments(vorbis.Bytes())
+	if commentMIME != "image/png" || !bytes.Equal(commentImage, png) {
+		t.Fatalf("vorbis picture = %s/%v", commentMIME, commentImage)
+	}
+	decoded := make([]byte, base64StdDecodeLen(len("SGV sbG8="))+4)
+	n, err := base64StdDecode(decoded, []byte("SGV sbG8="))
+	if err != nil || strings.TrimRight(string(decoded[:n]), "\x00") != "Hello" {
+		t.Fatalf("base64 decode = %q/%v", decoded[:n], err)
+	}
+
+	if detectOggStreamType([][]byte{[]byte("OpusHeadxxxx")}) != oggStreamOpus {
+		t.Fatal("expected opus stream")
+	}
+	if detectOggStreamType([][]byte{append([]byte{1}, []byte("vorbisxxxx")...)}) != oggStreamVorbis {
+		t.Fatal("expected vorbis stream")
+	}
+
+	mp3Path := filepath.Join(t.TempDir(), "quality.mp3")
+	audio := append([]byte{0xFF, 0xFB, 0x90, 0x64}, bytes.Repeat([]byte{0}, 2000)...)
+	if err := os.WriteFile(mp3Path, audio, 0600); err != nil {
+		t.Fatal(err)
+	}
+	quality, err := GetMP3Quality(mp3Path)
+	if err != nil || quality.SampleRate != 44100 || quality.Bitrate != 128000 {
+		t.Fatalf("MP3 quality = %#v/%v", quality, err)
+	}
+	if _, _, err := extractMP3CoverArt(filepath.Join(t.TempDir(), "missing.mp3")); err == nil {
+		t.Fatal("expected missing MP3 cover error")
+	}
+}
+
+func TestM4AMetadataAtomHelpers(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "tagged.m4a")
+	cover := []byte{0xFF, 0xD8, 0xFF, 0x00}
+	ilstPayload := []byte{}
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9nam", "M4A Title")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9ART", "M4A Artist")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9alb", "M4A Album")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("aART", "Album Artist")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9day", "2026")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9gen", "Pop")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9wrt", "Composer")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9cmt", "[ti:Comment Lyrics]")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("cprt", "Copyright")...)
+	ilstPayload = append(ilstPayload, buildM4ATextTag("\xa9lyr", "[00:00.00]M4A Lyrics")...)
+	ilstPayload = append(ilstPayload, buildM4AIndexTag("trkn", 3, 12)...)
+	ilstPayload = append(ilstPayload, buildM4AIndexTag("disk", 1, 2)...)
+	ilstPayload = append(ilstPayload, buildM4AFreeformAtom("ISRC", "USRC17607839")...)
+	ilstPayload = append(ilstPayload, buildM4AFreeformAtom("LABEL", "Label")...)
+	ilstPayload = append(ilstPayload, buildM4AFreeformAtom("REPLAYGAIN_TRACK_GAIN", "-6.50 dB")...)
+	ilstPayload = append(ilstPayload, buildM4AAtom("covr", buildM4AAtom("data", append([]byte{0, 0, 0, 13, 0, 0, 0, 0}, cover...)))...)
+	fileData := buildM4AFileWithIlst(ilstPayload, true)
+	if err := os.WriteFile(path, fileData, 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	meta, err := ReadM4ATags(path)
+	if err != nil {
+		t.Fatalf("ReadM4ATags: %v", err)
+	}
+	if meta.Title != "M4A Title" || meta.Artist != "M4A Artist" || meta.TrackNumber != 3 || meta.TotalTracks != 12 || meta.ISRC != "USRC17607839" {
+		t.Fatalf("M4A metadata = %#v", meta)
+	}
+	if lyrics, err := extractLyricsFromM4A(path); err != nil || !strings.Contains(lyrics, "M4A Lyrics") {
+		t.Fatalf("extractLyricsFromM4A = %q/%v", lyrics, err)
+	}
+	if image, err := extractCoverFromM4A(path); err != nil || !bytes.Equal(image, cover) {
+		t.Fatalf("extractCoverFromM4A = %#v/%v", image, err)
+	}
+	if pathInfo, err := func() (m4aMetadataPath, error) {
+		f, err := os.Open(path)
+		if err != nil {
+			return m4aMetadataPath{}, err
+		}
+		defer f.Close()
+		info, _ := f.Stat()
+		return findM4AMetadataPath(f, info.Size())
+	}(); err != nil || pathInfo.udta == nil {
+		t.Fatalf("findM4AMetadataPath = %#v/%v", pathInfo, err)
+	}
+	if err := EditM4AReplayGain(path, map[string]string{"replaygain_track_gain": "-5.00 dB", "replaygain_track_peak": "0.98"}); err != nil {
+		t.Fatalf("EditM4AReplayGain: %v", err)
+	}
+	edited, err := ReadM4ATags(path)
+	if err != nil || edited.ReplayGainTrackGain != "-5.00 dB" || edited.ReplayGainTrackPeak != "0.98" {
+		t.Fatalf("edited M4A = %#v/%v", edited, err)
+	}
+
+	noUdtaPath := filepath.Join(dir, "noudta.m4a")
+	if err := os.WriteFile(noUdtaPath, buildM4AFileWithIlst(buildM4ATextTag("\xa9nam", "No Udta"), false), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if meta, err := ReadM4ATags(noUdtaPath); err != nil || meta.Title != "No Udta" {
+		t.Fatalf("ReadM4ATags no udta = %#v/%v", meta, err)
+	}
+	if _, err := ReadM4ATags(filepath.Join(dir, "missing.m4a")); err == nil {
+		t.Fatal("expected missing M4A error")
+	}
+	emptyM4A := filepath.Join(dir, "empty.m4a")
+	if err := os.WriteFile(emptyM4A, buildM4AFileWithIlst(nil, true), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := ReadM4ATags(emptyM4A); err == nil {
+		t.Fatal("expected empty M4A tags error")
+	}
+	if _, err := extractCoverFromM4A(emptyM4A); err == nil {
+		t.Fatal("expected missing M4A cover error")
+	}
+	if _, err := extractLyricsFromM4A(emptyM4A); err == nil {
+		t.Fatal("expected missing M4A lyrics error")
+	}
+
+	sidecarAudio := filepath.Join(dir, "sidecar.mp3")
+	if err := os.WriteFile(sidecarAudio, []byte("audio"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "sidecar.lrc"), []byte(" [00:00.00]Sidecar "), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if lyrics, err := extractLyricsFromSidecarLRC(sidecarAudio); err != nil || !strings.Contains(lyrics, "Sidecar") {
+		t.Fatalf("sidecar lyrics = %q/%v", lyrics, err)
+	}
+	if !looksLikeEmbeddedLyrics("[ti:Song]") || !looksLikeEmbeddedLyrics("[00:00.00]Line\n[00:01.00]Next") || looksLikeEmbeddedLyrics("plain") {
+		t.Fatal("embedded lyric heuristic mismatch")
+	}
+	if formatIndexValue(3, 12) != "3/12" || formatIndexValue(3, 0) != "3" || formatIndexValue(0, 12) != "" {
+		t.Fatal("formatIndexValue mismatch")
+	}
+	if parsePositiveInt(" 42 ") != 42 || parsePositiveInt("bad") != 0 {
+		t.Fatal("parsePositiveInt mismatch")
+	}
+	if !hasMapKey(map[string]string{"x": "y"}, "x") {
+		t.Fatal("expected map key")
+	}
+	if _, ok := parseReplayGainDb("-6.50 dB"); !ok {
+		t.Fatal("expected ReplayGain dB parse")
+	}
+	if _, ok := parseReplayGainPeak("0.98"); !ok {
+		t.Fatal("expected ReplayGain peak parse")
+	}
+	if norm := buildITunNORMTag("-6.50 dB", "0.98"); norm == "" {
+		t.Fatal("expected iTunNORM")
+	}
+	if fields := collectM4AReplayGainFields(map[string]string{"replaygain_track_gain": "-6 dB", "replaygain_track_peak": "0.9"}); fields["iTunNORM"] == "" {
+		t.Fatalf("ReplayGain fields = %#v", fields)
+	}
+
+	qualityPath := filepath.Join(dir, "quality-alac.m4a")
+	mvhd := make([]byte, 20)
+	binary.BigEndian.PutUint32(mvhd[12:16], 1000)
+	binary.BigEndian.PutUint32(mvhd[16:20], 180000)
+	sampleEntry := make([]byte, 32)
+	copy(sampleEntry[0:4], "alac")
+	binary.BigEndian.PutUint16(sampleEntry[22:24], 24)
+	sampleEntry[28] = 0xAC
+	sampleEntry[29] = 0x44
+	alacConfig := make([]byte, 24)
+	alacConfig[5] = 24
+	binary.BigEndian.PutUint32(alacConfig[20:24], 44100)
+	alacEntryPayload := append(append([]byte{}, sampleEntry[4:]...), buildM4AAtom("alac", alacConfig)...)
+	qualityFile := append(buildM4AAtom("ftyp", []byte("M4A \x00\x00\x00\x00")), buildM4AAtom("moov", append(buildM4AAtom("mvhd", mvhd), buildM4AAtom("alac", alacEntryPayload)...))...)
+	if err := os.WriteFile(qualityPath, qualityFile, 0600); err != nil {
+		t.Fatal(err)
+	}
+	if quality, err := GetM4AQuality(qualityPath); err != nil || quality.BitDepth != 24 || quality.SampleRate != 44100 || quality.Duration != 180 {
+		t.Fatalf("GetM4AQuality = %#v/%v", quality, err)
+	}
+	if quality, err := GetAudioQuality(qualityPath); err != nil || quality.SampleRate != 44100 {
+		t.Fatalf("GetAudioQuality M4A = %#v/%v", quality, err)
+	}
+	aacQualityPath := filepath.Join(dir, "quality-aac.m4a")
+	copy(sampleEntry[0:4], "mp4a")
+	aacQualityFile := append(buildM4AAtom("ftyp", []byte("M4A \x00\x00\x00\x00")), buildM4AAtom("moov", append(buildM4AAtom("mvhd", mvhd), sampleEntry...))...)
+	if err := os.WriteFile(aacQualityPath, aacQualityFile, 0600); err != nil {
+		t.Fatal(err)
+	}
+	if quality, err := GetM4AQuality(aacQualityPath); err != nil || quality.BitDepth != 0 || quality.SampleRate != 44100 || quality.Duration != 180 {
+		t.Fatalf("GetM4AQuality AAC = %#v/%v", quality, err)
+	}
+	eac3QualityPath := filepath.Join(dir, "quality-eac3.m4a")
+	zeroMvhd := make([]byte, 20)
+	eac3SampleEntry := make([]byte, 32)
+	copy(eac3SampleEntry[0:4], "ec-3")
+	eac3SampleEntry[28] = 0xBB
+	eac3SampleEntry[29] = 0x80
+	mdhd := make([]byte, 20)
+	binary.BigEndian.PutUint32(mdhd[12:16], 48000)
+	binary.BigEndian.PutUint32(mdhd[16:20], 48000*123)
+	eac3QualityFile := append(
+		buildM4AAtom("ftyp", []byte("M4A \x00\x00\x00\x00")),
+		buildM4AAtom("moov", append(
+			append(buildM4AAtom("mvhd", zeroMvhd), buildM4AAtom("trak", buildM4AAtom("mdia", buildM4AAtom("mdhd", mdhd)))...),
+			eac3SampleEntry...,
+		))...,
+	)
+	if err := os.WriteFile(eac3QualityPath, eac3QualityFile, 0600); err != nil {
+		t.Fatal(err)
+	}
+	if quality, err := GetM4AQuality(eac3QualityPath); err != nil || quality.Codec != "eac3" || quality.Duration != 123 {
+		t.Fatalf("GetM4AQuality EAC3 mdhd fallback = %#v/%v", quality, err)
+	}
+	if _, _, ok := parseALACSpecificConfig(make([]byte, 4)); ok {
+		t.Fatal("short ALAC config should not parse")
+	}
+	alac := make([]byte, 24)
+	alac[5] = 16
+	binary.BigEndian.PutUint32(alac[20:24], 48000)
+	if depth, rate, ok := parseALACSpecificConfig(alac); !ok || depth != 16 || rate != 48000 {
+		t.Fatalf("ALAC config = %d/%d/%v", depth, rate, ok)
+	}
+}
+
+func TestOggMetadataQualityAndCoverHelpers(t *testing.T) {
+	dir := t.TempDir()
+	opusHead := make([]byte, 19)
+	copy(opusHead[0:8], "OpusHead")
+	binary.LittleEndian.PutUint16(opusHead[10:12], 312)
+	binary.LittleEndian.PutUint32(opusHead[12:16], 48000)
+
+	var comments bytes.Buffer
+	binary.Write(&comments, binary.LittleEndian, uint32(6))
+	comments.WriteString("vendor")
+	entries := []string{
+		"TITLE=Ogg Title",
+		"ARTIST=Artist",
+		"ALBUMARTIST=Album Artist",
+		"TRACKNUMBER=2/9",
+		"DISCNUMBER=1/2",
+		"LYRICS=[00:00.00]Ogg Lyrics",
+	}
+	binary.Write(&comments, binary.LittleEndian, uint32(len(entries)))
+	for _, entry := range entries {
+		binary.Write(&comments, binary.LittleEndian, uint32(len(entry)))
+		comments.WriteString(entry)
+	}
+	opusTags := append([]byte("OpusTags"), comments.Bytes()...)
+	oggPath := filepath.Join(dir, "tagged.opus")
+	oggData := append(buildOggPage(0x02, 0, opusHead), buildOggPage(0x00, 48000+312, opusTags)...)
+	if err := os.WriteFile(oggPath, oggData, 0600); err != nil {
+		t.Fatal(err)
+	}
+	quality, err := GetOggQuality(oggPath)
+	if err != nil || quality.SampleRate != 48000 || quality.Duration != 1 {
+		t.Fatalf("GetOggQuality = %#v/%v", quality, err)
+	}
+	meta, err := ReadOggVorbisComments(oggPath)
+	if err != nil || meta.Title != "Ogg Title" || meta.TrackNumber != 2 || meta.TotalTracks != 9 {
+		t.Fatalf("ReadOggVorbisComments = %#v/%v", meta, err)
+	}
+
+	picture := buildTestFLACPictureBlock([]byte{0x89, 0x50, 0x4E, 0x47}, "image/png")
+	pictureComment := "METADATA_BLOCK_PICTURE=" + base64.StdEncoding.EncodeToString(picture)
+	var coverComments bytes.Buffer
+	binary.Write(&coverComments, binary.LittleEndian, uint32(6))
+	coverComments.WriteString("vendor")
+	binary.Write(&coverComments, binary.LittleEndian, uint32(1))
+	binary.Write(&coverComments, binary.LittleEndian, uint32(len(pictureComment)))
+	coverComments.WriteString(pictureComment)
+	coverPath := filepath.Join(dir, "cover.opus")
+	coverData := append(buildOggPage(0x02, 0, opusHead), buildOggPage(0x00, 48000+312, append([]byte("OpusTags"), coverComments.Bytes()...))...)
+	if err := os.WriteFile(coverPath, coverData, 0600); err != nil {
+		t.Fatal(err)
+	}
+	if image, mime, err := extractOggCoverArt(coverPath); err != nil || mime != "image/png" || len(image) == 0 {
+		t.Fatalf("extractOggCoverArt = %s/%#v/%v", mime, image, err)
+	}
+	if image, mime, err := extractAnyCoverArtWithHint(coverPath, "cover.opus"); err != nil || mime != "image/png" || len(image) == 0 {
+		t.Fatalf("extractAnyCoverArtWithHint = %s/%#v/%v", mime, image, err)
+	}
+	if image, mime, err := extractAnyCoverArt(coverPath); err != nil || mime != "image/png" || len(image) == 0 {
+		t.Fatalf("extractAnyCoverArt = %s/%#v/%v", mime, image, err)
+	}
+	extractedCoverPath := filepath.Join(dir, "extracted.png")
+	if err := ExtractCoverToFile(coverPath, extractedCoverPath); err != nil {
+		t.Fatalf("ExtractCoverToFile = %v", err)
+	}
+	if data := mustReadFile(t, extractedCoverPath); len(data) == 0 {
+		t.Fatal("expected extracted cover data")
+	}
+	cachePath, err := SaveCoverToCacheWithHintAndKey(coverPath, "cover.opus", dir, "key")
+	if err != nil || cachePath == "" {
+		t.Fatalf("SaveCoverToCacheWithHintAndKey = %q/%v", cachePath, err)
+	}
+	cacheDir := filepath.Join(dir, "cache")
+	if path, err := SaveCoverToCache(coverPath, cacheDir); err != nil || !strings.HasSuffix(path, ".png") {
+		t.Fatalf("SaveCoverToCache = %q/%v", path, err)
+	}
+	if path, err := SaveCoverToCacheWithHint(coverPath, "cover.opus", cacheDir); err != nil || path == "" {
+		t.Fatalf("SaveCoverToCacheWithHint = %q/%v", path, err)
+	}
+	hitPath, err := SaveCoverToCache(coverPath, cacheDir)
+	if err != nil || hitPath == "" {
+		t.Fatalf("SaveCoverToCache cache hit = %q/%v", hitPath, err)
+	}
+	if _, err := SaveCoverToCacheWithHintAndKey(filepath.Join(dir, "missing.opus"), "missing.opus", dir, "missing"); err == nil {
+		t.Fatal("expected missing cover cache error")
+	}
+
+	badPath := filepath.Join(dir, "bad.ogg")
+	if err := os.WriteFile(badPath, []byte("bad"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := GetOggQuality(badPath); err == nil {
+		t.Fatal("expected invalid Ogg quality error")
+	}
+}
+
+func buildM4ADataPayload(payload []byte) []byte {
+	return append([]byte{0, 0, 0, 1, 0, 0, 0, 0}, payload...)
+}
+
+func buildM4ATextTag(atomType, value string) []byte {
+	return buildM4AAtom(atomType, buildM4AAtom("data", buildM4ADataPayload([]byte(value))))
+}
+
+func buildM4AIndexTag(atomType string, number, total int) []byte {
+	payload := []byte{0, 0, 0, byte(number), 0, byte(total), 0, 0}
+	return buildM4AAtom(atomType, buildM4AAtom("data", buildM4ADataPayload(payload)))
+}
+
+func buildM4AFileWithIlst(ilstPayload []byte, withUdta bool) []byte {
+	ilst := buildM4AAtom("ilst", ilstPayload)
+	meta := buildM4AAtom("meta", append([]byte{0, 0, 0, 0}, ilst...))
+	moovPayload := meta
+	if withUdta {
+		moovPayload = buildM4AAtom("udta", meta)
+	}
+	return append(buildM4AAtom("ftyp", []byte("M4A \x00\x00\x00\x00")), buildM4AAtom("moov", moovPayload)...)
+}
+
+func buildOggPage(headerType byte, granule uint64, packet []byte) []byte {
+	header := make([]byte, 27)
+	copy(header[0:4], "OggS")
+	header[4] = 0
+	header[5] = headerType
+	binary.LittleEndian.PutUint64(header[6:14], granule)
+	header[26] = 1
+	return append(append(header, byte(len(packet))), packet...)
+}
+
+func buildTestFLACPictureBlock(image []byte, mime string) []byte {
+	var picture bytes.Buffer
+	binary.Write(&picture, binary.BigEndian, uint32(3))
+	binary.Write(&picture, binary.BigEndian, uint32(len(mime)))
+	picture.WriteString(mime)
+	binary.Write(&picture, binary.BigEndian, uint32(0))
+	binary.Write(&picture, binary.BigEndian, uint32(1))
+	binary.Write(&picture, binary.BigEndian, uint32(1))
+	binary.Write(&picture, binary.BigEndian, uint32(32))
+	binary.Write(&picture, binary.BigEndian, uint32(0))
+	binary.Write(&picture, binary.BigEndian, uint32(len(image)))
+	picture.Write(image)
+	return picture.Bytes()
+}
@@ -9,14 +9,23 @@ import (
 // ErrDownloadCancelled is returned when a download is cancelled by the user.
 var ErrDownloadCancelled = errors.New("download cancelled")

+// ErrExtensionRequestCancelled is returned when a UI-driven extension request
+// is superseded by a newer home/search request.
+var ErrExtensionRequestCancelled = errors.New("extension request cancelled")
+
 type cancelEntry struct {
+	ctx      context.Context
 	cancel   context.CancelFunc
 	canceled bool
+	refs     int
 }

 var (
 	cancelMu  sync.Mutex
 	cancelMap = make(map[string]*cancelEntry)
+
+	extensionRequestCancelMu  sync.Mutex
+	extensionRequestCancelMap = make(map[string]*cancelEntry)
 )

 func initDownloadCancel(itemID string) context.Context {
@@ -27,10 +36,25 @@ func initDownloadCancel(itemID string) context.Context {
 	cancelMu.Lock()
 	defer cancelMu.Unlock()

+	if entry, ok := cancelMap[itemID]; ok {
+		if entry.ctx == nil {
+			ctx, cancel := context.WithCancel(context.Background())
+			entry.ctx = ctx
+			entry.cancel = cancel
+			if entry.canceled && entry.cancel != nil {
+				entry.cancel()
+			}
+		}
+		entry.refs++
+		return entry.ctx
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	cancelMap[itemID] = &cancelEntry{
+		ctx:      ctx,
 		cancel:   cancel,
 		canceled: false,
+		refs:     1,
 	}
 	return ctx
 }
@@ -73,6 +97,86 @@ func clearDownloadCancel(itemID string) {
 	}

 	cancelMu.Lock()
-	delete(cancelMap, itemID)
+	if entry, ok := cancelMap[itemID]; ok {
+		entry.refs--
+		if entry.refs <= 0 {
+			delete(cancelMap, itemID)
+		}
+	}
 	cancelMu.Unlock()
 }
+
+func initExtensionRequestCancel(requestID string) context.Context {
+	if requestID == "" {
+		return context.Background()
+	}
+
+	extensionRequestCancelMu.Lock()
+	defer extensionRequestCancelMu.Unlock()
+
+	if entry, ok := extensionRequestCancelMap[requestID]; ok {
+		if entry.ctx == nil {
+			ctx, cancel := context.WithCancel(context.Background())
+			entry.ctx = ctx
+			entry.cancel = cancel
+			if entry.canceled && entry.cancel != nil {
+				entry.cancel()
+			}
+		}
+		entry.refs++
+		return entry.ctx
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	extensionRequestCancelMap[requestID] = &cancelEntry{
+		ctx:      ctx,
+		cancel:   cancel,
+		canceled: false,
+		refs:     1,
+	}
+	return ctx
+}
+
+func cancelExtensionRequest(requestID string) {
+	if requestID == "" {
+		return
+	}
+
+	extensionRequestCancelMu.Lock()
+	if entry, ok := extensionRequestCancelMap[requestID]; ok {
+		entry.canceled = true
+		if entry.cancel != nil {
+			entry.cancel()
+		}
+	} else {
+		extensionRequestCancelMap[requestID] = &cancelEntry{canceled: true}
+	}
+	extensionRequestCancelMu.Unlock()
+}
+
+func isExtensionRequestCancelled(requestID string) bool {
+	if requestID == "" {
+		return false
+	}
+
+	extensionRequestCancelMu.Lock()
+	entry, ok := extensionRequestCancelMap[requestID]
+	canceled := ok && entry.canceled
+	extensionRequestCancelMu.Unlock()
+	return canceled
+}
+
+func clearExtensionRequestCancel(requestID string) {
+	if requestID == "" {
+		return
+	}
+
+	extensionRequestCancelMu.Lock()
+	if entry, ok := extensionRequestCancelMap[requestID]; ok {
+		entry.refs--
+		if entry.refs <= 0 {
+			delete(extensionRequestCancelMap, requestID)
+		}
+	}
+	extensionRequestCancelMu.Unlock()
+}
@@ -17,6 +17,10 @@ const (
 // Deezer CDN supports these sizes: 56, 250, 500, 1000, 1400, 1800
 var deezerSizeRegex = regexp.MustCompile(`/(\d+)x(\d+)-\d+-\d+-\d+-\d+\.jpg$`)

+var tidalSizeRegex = regexp.MustCompile(`/\d+x\d+\.jpg$`)
+
+var qobuzSizeRegex = regexp.MustCompile(`_\d+\.jpg$`)
+
 func convertSmallToMedium(imageURL string) string {
 	if strings.Contains(imageURL, spotifySize300) {
 		return strings.Replace(imageURL, spotifySize300, spotifySize640, 1)
@@ -40,7 +44,6 @@ func downloadCoverToMemory(coverURL string, maxQuality bool) ([]byte, error) {
 		maxURL := upgradeToMaxQuality(downloadURL)
 		if maxURL != downloadURL {
 			downloadURL = maxURL
-			// Log already printed by upgradeToMaxQuality for Deezer
 			if strings.Contains(coverURL, "scdn.co") || strings.Contains(coverURL, "spotifycdn") {
 				GoLog("[Cover] Spotify: upgraded to max resolution (~2000x2000)")
 			}
@@ -86,16 +89,22 @@ func downloadCoverToMemory(coverURL string, maxQuality bool) ([]byte, error) {
 }

 func upgradeToMaxQuality(coverURL string) string {
-	// Spotify CDN upgrade
 	if strings.Contains(coverURL, spotifySize640) {
 		return strings.Replace(coverURL, spotifySize640, spotifySizeMax, 1)
 	}

-	// Deezer CDN upgrade
 	if strings.Contains(coverURL, "cdn-images.dzcdn.net") {
 		return upgradeDeezerCover(coverURL)
 	}

+	if strings.Contains(coverURL, "resources.tidal.com") {
+		return upgradeTidalCover(coverURL)
+	}
+
+	if strings.Contains(coverURL, "static.qobuz.com") {
+		return upgradeQobuzCover(coverURL)
+	}
+
 	return coverURL
 }

@@ -111,12 +120,35 @@ func upgradeDeezerCover(coverURL string) string {
 	return upgraded
 }

+func upgradeTidalCover(coverURL string) string {
+	if !strings.Contains(coverURL, "resources.tidal.com") {
+		return coverURL
+	}
+
+	upgraded := tidalSizeRegex.ReplaceAllString(coverURL, "/origin.jpg")
+	if upgraded != coverURL {
+		GoLog("[Cover] Tidal: upgraded to origin resolution")
+	}
+	return upgraded
+}
+
+func upgradeQobuzCover(coverURL string) string {
+	if !strings.Contains(coverURL, "static.qobuz.com") {
+		return coverURL
+	}
+
+	upgraded := qobuzSizeRegex.ReplaceAllString(coverURL, "_max.jpg")
+	if upgraded != coverURL {
+		GoLog("[Cover] Qobuz: upgraded to max resolution")
+	}
+	return upgraded
+}
+
 func GetCoverFromSpotify(imageURL string, maxQuality bool) string {
 	if imageURL == "" {
 		return ""
 	}

-	// Always upgrade small to medium first
 	result := convertSmallToMedium(imageURL)

 	if maxQuality {
@@ -0,0 +1,401 @@
+package gobackend
+
+import (
+	"archive/zip"
+	"bytes"
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func newTestLoadedExtension(t *testing.T, types ...ExtensionType) *loadedExtension {
+	t.Helper()
+	dir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(dir, "index.js"), []byte(testExtensionJS), 0600); err != nil {
+		t.Fatalf("write index.js: %v", err)
+	}
+	return &loadedExtension{
+		ID: "coverage-ext",
+		Manifest: &ExtensionManifest{
+			Name:        "coverage-ext",
+			Description: "Coverage extension",
+			Version:     "1.0.0",
+			Types:       types,
+			Permissions: ExtensionPermissions{File: true, Network: []string{"example.test"}},
+			SearchBehavior: &SearchBehaviorConfig{
+				Enabled:     true,
+				Placeholder: "Search coverage",
+				Primary:     true,
+				Icon:        "search",
+			},
+			URLHandler:    &URLHandlerConfig{Enabled: true, Patterns: []string{"https://example.test/"}},
+			TrackMatching: &TrackMatchingConfig{CustomMatching: true},
+			PostProcessing: &PostProcessingConfig{
+				Enabled: true,
+				Hooks:   []PostProcessingHook{{ID: "hook", Name: "Hook", DefaultEnabled: true, SupportedFormats: []string{"flac"}}},
+			},
+		},
+		Enabled:   true,
+		SourceDir: dir,
+		DataDir:   t.TempDir(),
+	}
+}
+
+const testExtensionJS = `
+function track(id) {
+  return {
+    id: id,
+    name: "Track " + id,
+    artists: "Artist",
+    albumName: "Album",
+    albumArtist: "Album Artist",
+    durationMs: 180000,
+    coverUrl: "https://example.test/cover.jpg",
+    releaseDate: "2026-05-04",
+    trackNumber: 1,
+    totalTracks: 10,
+    discNumber: 1,
+    totalDiscs: 1,
+    isrc: "USRC17607839",
+    itemType: "track",
+    albumType: "album",
+    tidalId: "tidal-1",
+    qobuzId: "qobuz-1",
+    deezerId: "deezer-1",
+    spotifyId: "spotify:track:1",
+    externalLinks: { tidal: "https://tidal.example/1" },
+    label: "Label",
+    copyright: "Copyright",
+    genre: "Pop",
+    composer: "Composer",
+    audioQuality: "FLAC 24-bit",
+    audioModes: "DOLBY_ATMOS"
+  };
+}
+
+registerExtension({
+  searchTracks: function(query, limit) {
+    return { tracks: [track("search-1")], total: 1 };
+  },
+  customSearch: function(query, options) {
+    var t = track("custom-1");
+    t.name = "Custom " + query;
+    return [t];
+  },
+  getHomeFeed: function() {
+    return [{ id: "home-1", title: "Home", tracks: [track("home-track")] }];
+  },
+  getBrowseCategories: function() {
+    return [{ id: "cat-1", title: "Category" }];
+  },
+  getTrack: function(id) {
+    return track(id);
+  },
+  getAlbum: function(id) {
+    return {
+      id: id,
+      name: "Album " + id,
+      artists: "Artist",
+      artistId: "artist-1",
+      coverUrl: "https://example.test/album.jpg",
+      releaseDate: "2026-05-04",
+      totalTracks: 1,
+      albumType: "album",
+      tracks: [track("album-track")]
+    };
+  },
+  getPlaylist: function(id) {
+    return {
+      id: id,
+      name: "Playlist " + id,
+      artists: "Owner",
+      coverUrl: "https://example.test/playlist.jpg",
+      totalTracks: 1,
+      tracks: [track("playlist-track")]
+    };
+  },
+  getArtist: function(id) {
+    return {
+      id: id,
+      name: "Artist",
+      imageUrl: "https://example.test/artist.jpg",
+      headerImage: "https://example.test/header.jpg",
+      listeners: 123,
+      albums: [{ id: "album-1", name: "Album", artists: "Artist", totalTracks: 1 }],
+      releases: [{ id: "release-1", name: "Release", artists: "Artist", totalTracks: 1, tracks: [track("release-track")] }],
+      topTracks: [track("top-track")]
+    };
+  },
+  enrichTrack: function(input) {
+    var t = track(input.id || "enriched");
+    t.name = "Enriched";
+    return t;
+  },
+  checkAvailability: function(isrc, name, artist, ids) {
+    return { available: true, reason: "ok", trackId: "download-track", skipFallback: true };
+  },
+  getDownloadUrl: function(id, quality) {
+    return { url: "https://example.test/audio.flac", format: "flac", bitDepth: 24, sampleRate: 96000 };
+  },
+  download: function(id, quality, outputPath, onProgress) {
+    if (onProgress) onProgress(100);
+    return {
+      success: true,
+      filePath: "EXISTS:" + outputPath,
+      alreadyExists: false,
+      bitDepth: 24,
+      sampleRate: 96000,
+      title: "Downloaded",
+      artist: "Artist",
+      album: "Album",
+      albumArtist: "Album Artist",
+      trackNumber: 1,
+      totalTracks: 10,
+      discNumber: 1,
+      totalDiscs: 1,
+      releaseDate: "2026-05-04",
+      coverUrl: "https://example.test/cover.jpg",
+      isrc: "USRC17607839",
+      genre: "Pop",
+      label: "Label",
+      copyright: "Copyright",
+      composer: "Composer",
+      lyricsLrc: "[00:00.00]Hello",
+      decryptionKey: "001122",
+      decryption: { strategy: "mp4_decryption_key", options: { kid: "1" } }
+    };
+  },
+  fetchLyrics: function(name, artist, album, duration) {
+    return { syncType: "LINE_SYNCED", provider: "coverage-ext", lines: [{ startTimeMs: 0, endTimeMs: 1000, words: "Hello" }] };
+  },
+  handleUrl: function(url) {
+    return { type: "track", name: "Handled", coverUrl: "https://example.test/cover.jpg", track: track("url-track"), tracks: [track("url-track")], album: this.getAlbum("url-album"), artist: this.getArtist("url-artist") };
+  },
+  matchTrack: function(req) {
+    return { matched: true, trackId: "download-track", confidence: 0.95, reason: "exact" };
+  },
+  postProcess: function(path, req) {
+    return { success: true, newFilePath: path, bitDepth: 24, sampleRate: 96000 };
+  },
+  postProcessV2: function(input, metadata, hookId) {
+    return { success: true, newFilePath: input.path || input.uri, newFileUri: input.uri || "", bitDepth: 24, sampleRate: 96000 };
+  }
+});
+`
+
+func mustReadFile(t *testing.T, path string) []byte {
+	t.Helper()
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read file: %v", err)
+	}
+	return data
+}
+
+func buildID3v23Tag(frames ...[]byte) []byte {
+	body := bytes.Join(frames, nil)
+	header := []byte{'I', 'D', '3', 3, 0, 0, 0, 0, 0, 0}
+	copy(header[6:10], syncsafeBytes(len(body)))
+	return append(header, body...)
+}
+
+func id3TextFrame(id, value string) []byte {
+	return id3v23Frame(id, append([]byte{3}, []byte(value)...))
+}
+
+func id3CommentFrame(id, value string) []byte {
+	payload := append([]byte{3, 'e', 'n', 'g', 0}, []byte(value)...)
+	return id3v23Frame(id, payload)
+}
+
+func id3UserTextFrame(id, desc, value string) []byte {
+	payload := append([]byte{3}, []byte(desc)...)
+	payload = append(payload, 0)
+	payload = append(payload, []byte(value)...)
+	return id3v23Frame(id, payload)
+}
+
+func id3v23Frame(id string, payload []byte) []byte {
+	frame := make([]byte, 10+len(payload))
+	copy(frame[0:4], id)
+	binary.BigEndian.PutUint32(frame[4:8], uint32(len(payload)))
+	copy(frame[10:], payload)
+	return frame
+}
+
+func buildID3v22Tag(frames ...[]byte) []byte {
+	body := bytes.Join(frames, nil)
+	header := []byte{'I', 'D', '3', 2, 0, 0, 0, 0, 0, 0}
+	copy(header[6:10], syncsafeBytes(len(body)))
+	return append(header, body...)
+}
+
+func id3v22TextFrame(id, value string) []byte {
+	return id3v22Frame(id, append([]byte{3}, []byte(value)...))
+}
+
+func id3v22CommentFrame(id, value string) []byte {
+	payload := append([]byte{3, 'e', 'n', 'g', 0}, []byte(value)...)
+	return id3v22Frame(id, payload)
+}
+
+func id3v22Frame(id string, payload []byte) []byte {
+	frame := make([]byte, 6+len(payload))
+	copy(frame[0:3], id)
+	size := len(payload)
+	frame[3] = byte(size >> 16)
+	frame[4] = byte(size >> 8)
+	frame[5] = byte(size)
+	copy(frame[6:], payload)
+	return frame
+}
+
+func syncsafeBytes(size int) []byte {
+	return []byte{
+		byte((size >> 21) & 0x7f),
+		byte((size >> 14) & 0x7f),
+		byte((size >> 7) & 0x7f),
+		byte(size & 0x7f),
+	}
+}
+
+func buildID3v1Tag(title, artist, album, year string, track, genre byte) []byte {
+	tag := make([]byte, 128)
+	copy(tag[0:3], "TAG")
+	copyPadded(tag[3:33], title)
+	copyPadded(tag[33:63], artist)
+	copyPadded(tag[63:93], album)
+	copyPadded(tag[93:97], year)
+	tag[125] = 0
+	tag[126] = track
+	tag[127] = genre
+	return tag
+}
+
+func copyPadded(dst []byte, value string) {
+	for i := range dst {
+		dst[i] = ' '
+	}
+	copy(dst, value)
+}
+
+func writeExportCueFixture(t *testing.T, dir string) (string, string) {
+	t.Helper()
+	audioPath := filepath.Join(dir, "exports.wav")
+	if err := os.WriteFile(audioPath, []byte("audio"), 0600); err != nil {
+		t.Fatalf("write export audio: %v", err)
+	}
+	cuePath := filepath.Join(dir, "exports.cue")
+	cue := "PERFORMER \"Artist\"\nTITLE \"Album\"\nFILE \"exports.wav\" WAVE\n  TRACK 01 AUDIO\n    TITLE \"Song\"\n    INDEX 01 00:00:00\n"
+	if err := os.WriteFile(cuePath, []byte(cue), 0600); err != nil {
+		t.Fatalf("write export cue: %v", err)
+	}
+	return cuePath, audioPath
+}
+
+func escapeJSONPath(path string) string {
+	data, _ := json.Marshal(path)
+	return strings.Trim(string(data), `"`)
+}
+
+func fakeDeezerResponse(path, rawQuery string) string {
+	switch {
+	case path == "/2.0/search/track":
+		if strings.Contains(rawQuery, "MISSING") {
+			return `{"data":[]}`
+		}
+		return `{"data":[` + fakeDeezerTrackJSON(101, true) + `]}`
+	case path == "/2.0/search/artist":
+		return `{"data":[{"id":301,"name":"Artist","picture_xl":"artist-xl","nb_fan":123}]}`
+	case path == "/2.0/search/album":
+		return `{"data":[{"id":201,"title":"Album","cover_xl":"album-xl","nb_tracks":2,"release_date":"2026-05-04","record_type":"compile","artist":{"id":301,"name":"Artist"}}]}`
+	case path == "/2.0/search/playlist":
+		return `{"data":[{"id":401,"title":"Playlist","picture_xl":"playlist-xl","nb_tracks":2,"user":{"name":"Owner"}}]}`
+	case path == "/2.0/track/101", path == "/2.0/track/isrc:USRC17607839":
+		return fakeDeezerTrackJSON(101, true)
+	case path == "/2.0/track/102":
+		return fakeDeezerTrackJSON(102, true)
+	case path == "/2.0/track/isrc:MISSING":
+		return `{"id":0}`
+	case path == "/2.0/album/201":
+		return `{"id":201,"title":"Album","cover_xl":"album-xl","release_date":"2026-05-04","nb_tracks":2,"record_type":"compile","label":"Label","copyright":"Copyright","genres":{"data":[{"name":"Pop"},{"name":"Dance"}]},"artist":{"id":301,"name":"Album Artist"},"contributors":[{"name":"Contributor A"},{"name":"Contributor B"}],"tracks":{"data":[` + fakeDeezerTrackJSON(101, true) + `,` + fakeDeezerTrackJSON(102, false) + `]}}`
+	case path == "/2.0/artist/301":
+		return `{"id":301,"name":"Artist","picture_xl":"artist-xl","nb_fan":123,"nb_album":1}`
+	case path == "/2.0/artist/301/albums":
+		return `{"data":[{"id":201,"title":"Album","release_date":"2026-05-04","nb_tracks":0,"cover_xl":"album-xl","record_type":"compile"}]}`
+	case path == "/2.0/artist/301/related":
+		return `{"data":[{"id":302,"name":"Related","picture_xl":"related-xl","nb_fan":10}]}`
+	case path == "/2.0/playlist/401":
+		return `{"id":401,"title":"Playlist","picture_xl":"playlist-xl","nb_tracks":2,"creator":{"name":"Owner"},"tracks":{"data":[` + fakeDeezerTrackJSON(101, true) + `,` + fakeDeezerTrackJSON(102, false) + `]}}`
+	default:
+		return ""
+	}
+}
+
+func fakeDeezerTrackJSON(id int, withISRC bool) string {
+	isrc := ""
+	if withISRC {
+		isrc = `,"isrc":"USRC17607839"`
+		if id == 102 {
+			isrc = `,"isrc":"USRC17607840"`
+		}
+	}
+	return fmt.Sprintf(`{"id":%d,"title":"Track %d","duration":180,"track_position":%d,"disk_number":1%s,"link":"https://deezer.test/track/%d","release_date":"2026-05-04","artist":{"id":301,"name":"Artist"},"contributors":[{"name":"Contributor A"},{"name":"Contributor B"}],"album":{"id":201,"title":"Album","cover_xl":"album-xl","release_date":"2026-05-04","record_type":"album"}}`, id, id, id-100, isrc, id)
+}
+
+func createTestExtensionPackage(t *testing.T, path, name, version, js string, extraFiles map[string]string) {
+	t.Helper()
+	out, err := os.Create(path)
+	if err != nil {
+		t.Fatalf("create extension package: %v", err)
+	}
+	defer out.Close()
+
+	zw := zip.NewWriter(out)
+	defer zw.Close()
+
+	manifest := fmt.Sprintf(`{
+		"name": %q,
+		"displayName": %q,
+		"version": %q,
+		"description": "Packaged test extension",
+		"type": ["metadata_provider", "download_provider", "lyrics_provider"],
+		"permissions": {"network": ["example.test"], "storage": true, "file": true},
+		"icon": "icon.png",
+		"settings": [{"key":"quality","type":"string","label":"Quality"}],
+		"qualityOptions": [{"id":"lossless","label":"Lossless","description":"Lossless"}],
+		"searchBehavior": {"enabled": true, "placeholder": "Search", "primary": true},
+		"urlHandler": {"enabled": true, "patterns": ["https://example.test/"]},
+		"trackMatching": {"customMatching": true},
+		"postProcessing": {"enabled": true, "hooks": [{"id":"hook","name":"Hook"}]},
+		"serviceHealth": [{"id":"main","url":"https://example.test/health"}],
+		"capabilities": {"homeFeed": true}
+	}`, name, name, version)
+
+	for fileName, content := range map[string]string{
+		"manifest.json": manifest,
+		"index.js":      js,
+		"icon.png":      "png",
+	} {
+		writer, err := zw.Create(fileName)
+		if err != nil {
+			t.Fatalf("zip create %s: %v", fileName, err)
+		}
+		if _, err := writer.Write([]byte(content)); err != nil {
+			t.Fatalf("zip write %s: %v", fileName, err)
+		}
+	}
+	for fileName, content := range extraFiles {
+		writer, err := zw.Create(fileName)
+		if err != nil {
+			t.Fatalf("zip create extra %s: %v", fileName, err)
+		}
+		if _, err := writer.Write([]byte(content)); err != nil {
+			t.Fatalf("zip write extra %s: %v", fileName, err)
+		}
+	}
+}
@@ -0,0 +1,442 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"sort"
+	"strings"
+	"sync"
+)
+
+type CrossExtensionShareResult struct {
+	ExtensionID string `json:"extension_id"`
+	DisplayName string `json:"display_name"`
+	Found       bool   `json:"found"`
+	URL         string `json:"url,omitempty"`
+	ItemName    string `json:"item_name,omitempty"`
+	ItemArtists string `json:"item_artists,omitempty"`
+	Error       string `json:"error,omitempty"`
+}
+
+var crossExtensionShareResultCache = struct {
+	sync.RWMutex
+	entries map[string]string
+	order   []string
+}{
+	entries: make(map[string]string),
+}
+
+const crossExtensionShareResultCacheLimit = 128
+
+func FindCollectionAcrossExtensionsJSON(requestJSON string) (string, error) {
+	var req struct {
+		Name              string `json:"name"`
+		Artists           string `json:"artists"`
+		Type              string `json:"type"`
+		SourceExtensionID string `json:"source_extension_id"`
+	}
+	if err := json.Unmarshal([]byte(requestJSON), &req); err != nil {
+		return "", err
+	}
+
+	req.Name = strings.TrimSpace(req.Name)
+	req.Artists = strings.TrimSpace(req.Artists)
+	req.Type = strings.ToLower(strings.TrimSpace(req.Type))
+	req.SourceExtensionID = strings.TrimSpace(req.SourceExtensionID)
+	if req.Name == "" {
+		return "[]", nil
+	}
+	if req.Type == "" {
+		req.Type = "album"
+	}
+
+	providers := getExtensionManager().GetMetadataProviders()
+	work := make([]*extensionProviderWrapper, 0, len(providers))
+	for _, provider := range providers {
+		if provider == nil || provider.extension == nil {
+			continue
+		}
+		if provider.extension.ID == req.SourceExtensionID {
+			continue
+		}
+		work = append(work, provider)
+	}
+	cacheKey := crossExtensionShareCacheKey(req.Name, req.Artists, req.Type, req.SourceExtensionID, work)
+	if cached := getCrossExtensionShareCache(cacheKey); cached != "" {
+		return cached, nil
+	}
+
+	query := req.Name
+	if req.Artists != "" {
+		query += " " + req.Artists
+	}
+
+	results := make([]CrossExtensionShareResult, len(work))
+	var wg sync.WaitGroup
+	for i, provider := range work {
+		wg.Add(1)
+		go func(index int, p *extensionProviderWrapper) {
+			defer wg.Done()
+			results[index] = findCollectionForExtension(
+				p,
+				req.Type,
+				req.Name,
+				req.Artists,
+				query,
+			)
+		}(i, provider)
+	}
+	wg.Wait()
+
+	data, err := json.Marshal(results)
+	if err != nil {
+		return "[]", err
+	}
+	response := string(data)
+	if crossExtensionShareResultsCacheable(results) {
+		setCrossExtensionShareCache(cacheKey, response)
+	}
+	return response, nil
+}
+
+func crossExtensionShareCacheKey(name string, artists string, itemType string, sourceExtensionID string, providers []*extensionProviderWrapper) string {
+	providerKeys := make([]string, 0, len(providers))
+	for _, provider := range providers {
+		if provider == nil || provider.extension == nil {
+			continue
+		}
+		ext := provider.extension
+		displayName := ""
+		if ext.Manifest != nil {
+			displayName = ext.Manifest.DisplayName
+		}
+		providerKeys = append(providerKeys, strings.Join([]string{
+			strings.TrimSpace(ext.ID),
+			strings.TrimSpace(displayName),
+			strings.TrimSpace(ext.SourceDir),
+		}, "\x1f"))
+	}
+	sort.Strings(providerKeys)
+
+	return strings.Join([]string{
+		normalizeLooseTitle(itemType),
+		normalizeLooseTitle(name),
+		normalizeLooseArtistName(artists),
+		strings.TrimSpace(sourceExtensionID),
+		strings.Join(providerKeys, "\x1e"),
+	}, "\x1d")
+}
+
+func getCrossExtensionShareCache(key string) string {
+	if key == "" {
+		return ""
+	}
+	crossExtensionShareResultCache.RLock()
+	defer crossExtensionShareResultCache.RUnlock()
+	return crossExtensionShareResultCache.entries[key]
+}
+
+func setCrossExtensionShareCache(key string, value string) {
+	if key == "" || value == "" {
+		return
+	}
+	crossExtensionShareResultCache.Lock()
+	defer crossExtensionShareResultCache.Unlock()
+
+	if _, exists := crossExtensionShareResultCache.entries[key]; !exists {
+		crossExtensionShareResultCache.order = append(crossExtensionShareResultCache.order, key)
+	}
+	crossExtensionShareResultCache.entries[key] = value
+
+	for len(crossExtensionShareResultCache.order) > crossExtensionShareResultCacheLimit {
+		oldest := crossExtensionShareResultCache.order[0]
+		crossExtensionShareResultCache.order = crossExtensionShareResultCache.order[1:]
+		delete(crossExtensionShareResultCache.entries, oldest)
+	}
+}
+
+func crossExtensionShareResultsCacheable(results []CrossExtensionShareResult) bool {
+	for _, result := range results {
+		if result.Found {
+			continue
+		}
+		errText := strings.ToLower(strings.TrimSpace(result.Error))
+		if errText == "" ||
+			errText == "no results" ||
+			errText == "unsupported collection type" ||
+			strings.HasSuffix(errText, " not found") ||
+			strings.Contains(errText, "found without shareable link") {
+			continue
+		}
+		return false
+	}
+	return true
+}
+
+func findCollectionForExtension(
+	provider *extensionProviderWrapper,
+	itemType string,
+	name string,
+	artists string,
+	query string,
+) CrossExtensionShareResult {
+	result := CrossExtensionShareResult{
+		ExtensionID: provider.extension.ID,
+	}
+	if provider.extension.Manifest != nil {
+		result.DisplayName = provider.extension.Manifest.DisplayName
+	}
+	if result.DisplayName == "" {
+		result.DisplayName = provider.extension.ID
+	}
+
+	searchResult, err := searchCollectionCandidates(provider, itemType, query)
+	if err != nil {
+		result.Error = err.Error()
+		return result
+	}
+	if searchResult == nil || len(searchResult.Tracks) == 0 {
+		result.Error = "no results"
+		return result
+	}
+
+	var best *ExtTrackMetadata
+	switch itemType {
+	case "artist":
+		best = bestArtistTrack(searchResult.Tracks, name)
+	case "album":
+		best = bestAlbumTrack(searchResult.Tracks, name, artists)
+	default:
+		result.Error = "unsupported collection type"
+		return result
+	}
+	if best == nil {
+		result.Error = itemType + " not found"
+		return result
+	}
+
+	url := resolveCollectionShareURL(provider.extension, itemType, best)
+	if url == "" {
+		result.Error = itemType + " found without shareable link"
+		return result
+	}
+
+	result.Found = true
+	result.URL = url
+	if itemType == "artist" {
+		result.ItemName = collectionArtistName(*best)
+	} else {
+		result.ItemName = collectionAlbumName(*best)
+		result.ItemArtists = best.Artists
+	}
+	return result
+}
+
+func searchCollectionCandidates(provider *extensionProviderWrapper, itemType string, query string) (*ExtSearchResult, error) {
+	filter := ""
+	switch itemType {
+	case "album":
+		filter = "albums"
+	case "artist":
+		filter = "artists"
+	}
+
+	if filter != "" {
+		tracks, err := provider.CustomSearch(query, map[string]interface{}{
+			"filter": filter,
+			"limit":  10,
+		})
+		if err == nil && len(tracks) > 0 {
+			return &ExtSearchResult{Tracks: tracks, Total: len(tracks)}, nil
+		}
+	}
+
+	return provider.SearchTracks(query, 10)
+}
+
+func bestAlbumTrack(tracks []ExtTrackMetadata, albumName string, artists string) *ExtTrackMetadata {
+	targetAlbum := normalizeLooseTitle(albumName)
+	targetArtists := normalizeLooseArtistName(artists)
+	bestScore := 0
+	bestIndex := -1
+
+	for i := range tracks {
+		track := tracks[i]
+		album := normalizeLooseTitle(collectionAlbumName(track))
+		trackArtists := normalizeLooseArtistName(track.Artists + " " + track.AlbumArtist)
+
+		score := 0
+		if isCollectionItemType(track, "album") {
+			score += 25
+		}
+		if album == targetAlbum {
+			score += 100
+		} else if album != "" && targetAlbum != "" && (strings.Contains(album, targetAlbum) || strings.Contains(targetAlbum, album)) {
+			score += 50
+		}
+		if targetArtists != "" && (strings.Contains(trackArtists, targetArtists) || strings.Contains(targetArtists, trackArtists)) {
+			score += 30
+		}
+		if score > bestScore {
+			bestScore = score
+			bestIndex = i
+		}
+	}
+
+	if bestIndex < 0 || bestScore < 50 {
+		return nil
+	}
+	return &tracks[bestIndex]
+}
+
+func bestArtistTrack(tracks []ExtTrackMetadata, artistName string) *ExtTrackMetadata {
+	targetArtist := normalizeLooseArtistName(artistName)
+	bestScore := 0
+	bestIndex := -1
+
+	for i := range tracks {
+		artist := normalizeLooseArtistName(collectionArtistName(tracks[i]))
+		score := 0
+		if isCollectionItemType(tracks[i], "artist") {
+			score += 25
+		}
+		if artist == targetArtist {
+			score += 100
+		} else if artist != "" && targetArtist != "" && (strings.Contains(artist, targetArtist) || strings.Contains(targetArtist, artist)) {
+			score += 60
+		}
+		if score > bestScore {
+			bestScore = score
+			bestIndex = i
+		}
+	}
+
+	if bestIndex < 0 || bestScore < 60 {
+		return nil
+	}
+	return &tracks[bestIndex]
+}
+
+func resolveCollectionShareURL(ext *loadedExtension, itemType string, track *ExtTrackMetadata) string {
+	if track == nil {
+		return ""
+	}
+
+	if itemType == "album" {
+		if isCollectionItemType(*track, "album") {
+			if url := normalizeShareURL(track.ExternalURL); url != "" {
+				return url
+			}
+		}
+		if url := normalizeShareURL(track.AlbumURL); url != "" {
+			return url
+		}
+		if url := urlFromExternalLinks(track.ExternalLinks, "album"); url != "" {
+			return url
+		}
+		if url := templateShareURL(ext, "album", firstNonEmptyString(track.AlbumID, collectionID(*track, "album"), track.AlbumURL)); url != "" {
+			return url
+		}
+		return ""
+	}
+
+	if isCollectionItemType(*track, "artist") {
+		if url := normalizeShareURL(track.ExternalURL); url != "" {
+			return url
+		}
+	}
+	if url := normalizeShareURL(track.ArtistURL); url != "" {
+		return url
+	}
+	if url := urlFromExternalLinks(track.ExternalLinks, "artist"); url != "" {
+		return url
+	}
+	if url := templateShareURL(ext, "artist", firstNonEmptyString(track.ArtistID, collectionID(*track, "artist"))); url != "" {
+		return url
+	}
+	return ""
+}
+
+func collectionAlbumName(track ExtTrackMetadata) string {
+	if isCollectionItemType(track, "album") {
+		return track.Name
+	}
+	return track.AlbumName
+}
+
+func collectionArtistName(track ExtTrackMetadata) string {
+	if isCollectionItemType(track, "artist") {
+		return track.Name
+	}
+	return track.Artists
+}
+
+func collectionID(track ExtTrackMetadata, itemType string) string {
+	if isCollectionItemType(track, itemType) {
+		return track.ID
+	}
+	return ""
+}
+
+func isCollectionItemType(track ExtTrackMetadata, itemType string) bool {
+	return strings.EqualFold(strings.TrimSpace(track.ItemType), itemType)
+}
+
+func normalizeShareURL(value string) string {
+	trimmed := strings.TrimSpace(value)
+	if strings.HasPrefix(trimmed, "http://") || strings.HasPrefix(trimmed, "https://") {
+		return trimmed
+	}
+	return ""
+}
+
+func urlFromExternalLinks(links map[string]string, preferredKey string) string {
+	for key, value := range links {
+		if strings.Contains(strings.ToLower(key), preferredKey) {
+			if url := normalizeShareURL(value); url != "" {
+				return url
+			}
+		}
+	}
+	return ""
+}
+
+func templateShareURL(ext *loadedExtension, itemType string, id string) string {
+	if ext == nil || ext.Manifest == nil || ext.Manifest.Capabilities == nil {
+		return ""
+	}
+	id = stripProviderPrefix(strings.TrimSpace(id))
+	if id == "" {
+		return ""
+	}
+
+	templates, ok := ext.Manifest.Capabilities["shareUrlTemplates"].(map[string]interface{})
+	if !ok {
+		return ""
+	}
+	rawTemplate, ok := templates[itemType].(string)
+	if !ok {
+		return ""
+	}
+	rawTemplate = strings.TrimSpace(rawTemplate)
+	if rawTemplate == "" {
+		return ""
+	}
+	return strings.ReplaceAll(rawTemplate, "{id}", id)
+}
+
+func stripProviderPrefix(id string) string {
+	if index := strings.Index(id, ":"); index > 0 && index < len(id)-1 {
+		return id[index+1:]
+	}
+	return id
+}
+
+func firstNonEmptyString(values ...string) string {
+	for _, value := range values {
+		trimmed := strings.TrimSpace(value)
+		if trimmed != "" {
+			return trimmed
+		}
+	}
+	return ""
+}
@@ -0,0 +1,100 @@
+package gobackend
+
+import "testing"
+
+func TestCrossExtensionShareUsesAlbumCollectionItems(t *testing.T) {
+	ext := &loadedExtension{
+		Manifest: &ExtensionManifest{
+			Capabilities: map[string]interface{}{
+				"shareUrlTemplates": map[string]interface{}{
+					"album": "https://music.apple.com/us/album/{id}",
+				},
+			},
+		},
+	}
+	tracks := []ExtTrackMetadata{
+		{
+			ID:       "1440783617",
+			Name:     "Nevermind",
+			Artists:  "Nirvana",
+			ItemType: "album",
+		},
+	}
+
+	best := bestAlbumTrack(tracks, "Nevermind", "Nirvana")
+	if best == nil {
+		t.Fatal("expected album collection item to match")
+	}
+	if url := resolveCollectionShareURL(ext, "album", best); url != "https://music.apple.com/us/album/1440783617" {
+		t.Fatalf("album share URL = %q", url)
+	}
+}
+
+func TestCrossExtensionShareUsesArtistCollectionItems(t *testing.T) {
+	ext := &loadedExtension{
+		Manifest: &ExtensionManifest{
+			Capabilities: map[string]interface{}{
+				"shareUrlTemplates": map[string]interface{}{
+					"artist": "https://music.youtube.com/browse/{id}",
+				},
+			},
+		},
+	}
+	tracks := []ExtTrackMetadata{
+		{
+			ID:       "UCrPe3hLA51968GwxHSZ1llw",
+			Name:     "Nirvana",
+			ItemType: "artist",
+		},
+	}
+
+	best := bestArtistTrack(tracks, "Nirvana")
+	if best == nil {
+		t.Fatal("expected artist collection item to match")
+	}
+	if url := resolveCollectionShareURL(ext, "artist", best); url != "https://music.youtube.com/browse/UCrPe3hLA51968GwxHSZ1llw" {
+		t.Fatalf("artist share URL = %q", url)
+	}
+}
+
+func TestCrossExtensionShareCacheKeyIsProviderOrderStable(t *testing.T) {
+	apple := &extensionProviderWrapper{
+		extension: &loadedExtension{
+			ID:        "apple",
+			SourceDir: "/extensions/apple",
+			Manifest:  &ExtensionManifest{DisplayName: "Apple Music"},
+		},
+	}
+	qobuz := &extensionProviderWrapper{
+		extension: &loadedExtension{
+			ID:        "qobuz",
+			SourceDir: "/extensions/qobuz",
+			Manifest:  &ExtensionManifest{DisplayName: "Qobuz"},
+		},
+	}
+
+	first := crossExtensionShareCacheKey("Nevermind", "Nirvana", "album", "spotify", []*extensionProviderWrapper{apple, qobuz})
+	second := crossExtensionShareCacheKey("Nevermind", "Nirvana", "album", "spotify", []*extensionProviderWrapper{qobuz, apple})
+	if first != second {
+		t.Fatalf("cache key should not depend on provider order:\n%s\n%s", first, second)
+	}
+}
+
+func TestCrossExtensionShareCacheableSkipsTransientErrors(t *testing.T) {
+	cacheable := []CrossExtensionShareResult{
+		{ExtensionID: "apple", Found: true, URL: "https://music.apple.com/us/album/1"},
+		{ExtensionID: "qobuz", Error: "album not found"},
+		{ExtensionID: "tidal", Error: "no results"},
+	}
+	if !crossExtensionShareResultsCacheable(cacheable) {
+		t.Fatal("expected found and deterministic not-found results to be cacheable")
+	}
+
+	transient := []CrossExtensionShareResult{
+		{ExtensionID: "apple", Found: true, URL: "https://music.apple.com/us/album/1"},
+		{ExtensionID: "qobuz", Error: "request failed: timeout"},
+	}
+	if crossExtensionShareResultsCacheable(transient) {
+		t.Fatal("expected transient extension errors to skip cache")
+	}
+}
@@ -0,0 +1,171 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestCueParserEndToEnd(t *testing.T) {
+	dir := t.TempDir()
+	audioPath := filepath.Join(dir, "album.wav")
+	if err := os.WriteFile(audioPath, []byte("audio"), 0600); err != nil {
+		t.Fatalf("write audio: %v", err)
+	}
+	cuePath := filepath.Join(dir, "album.cue")
+	cue := "\ufeffREM GENRE \"Pop\"\n" +
+		"REM DATE 2026\n" +
+		"REM COMMENT \"comment\"\n" +
+		"REM COMPOSER \"Album Composer\"\n" +
+		"PERFORMER \"Album Artist\"\n" +
+		"TITLE \"Album Title\"\n" +
+		"FILE \"album.wav\" WAVE\n" +
+		"  TRACK 01 AUDIO\n" +
+		"    TITLE \"First\"\n" +
+		"    PERFORMER \"Track Artist\"\n" +
+		"    ISRC USRC17607839\n" +
+		"    INDEX 01 00:00:00\n" +
+		"  TRACK 02 AUDIO\n" +
+		"    TITLE \"Second\"\n" +
+		"    SONGWRITER \"Track Composer\"\n" +
+		"    INDEX 00 03:00:00\n" +
+		"    INDEX 01 03:05:00\n"
+	if err := os.WriteFile(cuePath, []byte(cue), 0600); err != nil {
+		t.Fatalf("write cue: %v", err)
+	}
+
+	sheet, err := ParseCueFile(cuePath)
+	if err != nil {
+		t.Fatalf("ParseCueFile: %v", err)
+	}
+	if sheet.Performer != "Album Artist" || sheet.Title != "Album Title" || len(sheet.Tracks) != 2 {
+		t.Fatalf("sheet = %#v", sheet)
+	}
+	if got := parseCueTimestamp("01:02:37"); got <= 62 || got >= 63 {
+		t.Fatalf("timestamp = %f", got)
+	}
+	if got := formatCueTimestamp(3723.5); got != "01:02:03.500" {
+		t.Fatalf("format timestamp = %q", got)
+	}
+	if got := unquoteCue("  \"quoted\"  "); got != "quoted" {
+		t.Fatalf("unquote = %q", got)
+	}
+	fileName, fileType := parseCueFileLine("unquoted album.flac FLAC")
+	if fileName != "unquoted album.flac" || fileType != "FLAC" {
+		t.Fatalf("file line = %q/%q", fileName, fileType)
+	}
+
+	if resolved := ResolveCueAudioPath(cuePath, "album.flac"); resolved != audioPath {
+		t.Fatalf("resolved = %q want %q", resolved, audioPath)
+	}
+	info, err := BuildCueSplitInfo(cuePath, sheet, "")
+	if err != nil {
+		t.Fatalf("BuildCueSplitInfo: %v", err)
+	}
+	if info.Tracks[0].EndSec != 180 || info.Tracks[1].Composer != "Track Composer" {
+		t.Fatalf("split info = %#v", info.Tracks)
+	}
+
+	jsonText, err := ParseCueFileJSON(cuePath, "")
+	if err != nil {
+		t.Fatalf("ParseCueFileJSON: %v", err)
+	}
+	var decoded CueSplitInfo
+	if err := json.Unmarshal([]byte(jsonText), &decoded); err != nil {
+		t.Fatalf("decode cue json: %v", err)
+	}
+	if decoded.AudioPath != audioPath {
+		t.Fatalf("decoded audio path = %q", decoded.AudioPath)
+	}
+
+	results, err := ScanCueFileForLibraryExt(cuePath, "", "virtual/album.cue", 1234, "scan-time")
+	if err != nil {
+		t.Fatalf("ScanCueFileForLibraryExt: %v", err)
+	}
+	if len(results) != 2 || results[0].TrackName != "First" || results[0].Duration != 180 {
+		t.Fatalf("scan results = %#v", results)
+	}
+	if results[0].FilePath != "virtual/album.cue#track01" || results[0].Format != "cue+wav" {
+		t.Fatalf("scan path/format = %q/%q", results[0].FilePath, results[0].Format)
+	}
+
+	if _, err := ParseCueFile(filepath.Join(dir, "missing.cue")); err == nil {
+		t.Fatal("expected missing cue error")
+	}
+	emptyCue := filepath.Join(dir, "empty.cue")
+	if err := os.WriteFile(emptyCue, []byte("TITLE \"No tracks\""), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := ParseCueFile(emptyCue); err == nil {
+		t.Fatal("expected no tracks error")
+	}
+	missingDir := t.TempDir()
+	missingCuePath := filepath.Join(missingDir, "missing.cue")
+	if err := os.WriteFile(missingCuePath, []byte(cue), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := BuildCueSplitInfo(missingCuePath, &CueSheet{FileName: "missing.wav"}, ""); err == nil {
+		t.Fatal("expected missing audio error")
+	}
+	if _, err := resolveCueAudioPathForLibrary(cuePath, nil, ""); err == nil {
+		t.Fatal("expected nil sheet error")
+	}
+	if _, err := scanCueSheetForLibrary(cuePath, nil, audioPath, "", 0, "", ""); err == nil {
+		t.Fatal("expected nil scan sheet error")
+	}
+}
+
+func TestDuplicateIndexAndParallelExistence(t *testing.T) {
+	dir := t.TempDir()
+	filePath := filepath.Join(dir, "song.flac")
+	if err := os.WriteFile(filePath, []byte("audio"), 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	idx := &ISRCIndex{index: map[string]string{}, outputDir: dir, buildTime: time.Now()}
+	idx.Add("usrc17607839", filePath)
+	if got, ok := idx.lookup("USRC17607839"); !ok || got != filePath {
+		t.Fatalf("lookup = %q/%v", got, ok)
+	}
+	if got, err := idx.Lookup("usrc17607839"); err != nil || got != filePath {
+		t.Fatalf("Lookup = %q/%v", got, err)
+	}
+	idx.remove("usrc17607839")
+	if _, ok := idx.lookup("usrc17607839"); ok {
+		t.Fatal("expected removed ISRC")
+	}
+
+	isrcIndexCacheMu.Lock()
+	isrcIndexCache[dir] = idx
+	isrcIndexCacheMu.Unlock()
+	defer InvalidateISRCCache(dir)
+
+	AddToISRCIndex(dir, "USRC17607839", filePath)
+	if found, err := CheckISRCExists(dir, "USRC17607839"); err != nil || found != filePath {
+		t.Fatalf("CheckISRCExists = %q/%v", found, err)
+	}
+	if !CheckFileExists(filePath) || CheckFileExists(dir) || CheckFileExists(filepath.Join(dir, "missing.flac")) {
+		t.Fatal("unexpected file existence result")
+	}
+
+	tracksJSON := `[{"isrc":"USRC17607839","track_name":"Song","artist_name":"Artist"},{"isrc":"MISSING","track_name":"Other","artist_name":"Artist"}]`
+	resultJSON, err := CheckFilesExistParallel(dir, tracksJSON)
+	if err != nil {
+		t.Fatalf("CheckFilesExistParallel: %v", err)
+	}
+	var results []FileExistenceResult
+	if err := json.Unmarshal([]byte(resultJSON), &results); err != nil {
+		t.Fatalf("decode results: %v", err)
+	}
+	if !results[0].Exists || results[0].FilePath != filePath || results[1].Exists {
+		t.Fatalf("results = %#v", results)
+	}
+	if _, err := CheckFilesExistParallel(dir, `not-json`); err == nil {
+		t.Fatal("expected invalid json error")
+	}
+	if err := PreBuildISRCIndex(""); err == nil {
+		t.Fatal("expected empty dir error")
+	}
+}
@@ -11,9 +11,7 @@ import (
 	"strings"
 )

-// CueSheet represents a parsed .cue file
 type CueSheet struct {
-	// Album-level metadata
 	Performer string     `json:"performer"`
 	Title     string     `json:"title"`
 	FileName  string     `json:"file_name"`
@@ -25,19 +23,16 @@ type CueSheet struct {
 	Tracks    []CueTrack `json:"tracks"`
 }

-// CueTrack represents a single track in a cue sheet
 type CueTrack struct {
-	Number    int    `json:"number"`
-	Title     string `json:"title"`
-	Performer string `json:"performer"`
-	ISRC      string `json:"isrc,omitempty"`
-	Composer  string `json:"composer,omitempty"`
-	// Index positions in seconds (fractional)
+	Number    int     `json:"number"`
+	Title     string  `json:"title"`
+	Performer string  `json:"performer"`
+	ISRC      string  `json:"isrc,omitempty"`
+	Composer  string  `json:"composer,omitempty"`
 	StartTime float64 `json:"start_time"` // INDEX 01 in seconds
 	PreGap    float64 `json:"pre_gap"`    // INDEX 00 in seconds (or -1 if not present)
 }

-// CueSplitInfo represents the information needed to split a CUE+audio file
 type CueSplitInfo struct {
 	CuePath   string          `json:"cue_path"`
 	AudioPath string          `json:"audio_path"`
@@ -48,7 +43,6 @@ type CueSplitInfo struct {
 	Tracks    []CueSplitTrack `json:"tracks"`
 }

-// CueSplitTrack has the FFmpeg split parameters for a single track
 type CueSplitTrack struct {
 	Number   int     `json:"number"`
 	Title    string  `json:"title"`
@@ -64,7 +58,6 @@ var (
 	reQuoted     = regexp.MustCompile(`"([^"]*)"`)
 )

-// ParseCueFile parses a .cue file and returns a CueSheet
 func ParseCueFile(cuePath string) (*CueSheet, error) {
 	f, err := os.Open(cuePath)
 	if err != nil {
@@ -82,7 +75,6 @@ func ParseCueFile(cuePath string) (*CueSheet, error) {
 			continue
 		}

-		// Handle BOM at start of file
 		if strings.HasPrefix(line, "\xef\xbb\xbf") {
 			line = strings.TrimPrefix(line, "\xef\xbb\xbf")
 			line = strings.TrimSpace(line)
@@ -90,7 +82,6 @@ func ParseCueFile(cuePath string) (*CueSheet, error) {

 		upper := strings.ToUpper(line)

-		// REM commands (album-level metadata)
 		if strings.HasPrefix(upper, "REM ") {
 			matches := reRemCommand.FindStringSubmatch(line)
 			if len(matches) == 3 {
@@ -136,9 +127,6 @@ func ParseCueFile(cuePath string) (*CueSheet, error) {

 		if strings.HasPrefix(upper, "FILE ") {
 			rest := line[len("FILE "):]
-			// Extract filename and type
-			// Format: FILE "filename.flac" WAVE
-			// or: FILE filename.flac WAVE
 			fname, ftype := parseCueFileLine(rest)
 			sheet.FileName = fname
 			sheet.FileType = ftype
@@ -146,7 +134,6 @@ func ParseCueFile(cuePath string) (*CueSheet, error) {
 		}

 		if strings.HasPrefix(upper, "TRACK ") {
-			// Save previous track
 			if currentTrack != nil {
 				sheet.Tracks = append(sheet.Tracks, *currentTrack)
 			}
@@ -184,7 +171,6 @@ func ParseCueFile(cuePath string) (*CueSheet, error) {
 			continue
 		}

-		// SONGWRITER (used as composer sometimes)
 		if strings.HasPrefix(upper, "SONGWRITER ") {
 			value := unquoteCue(line[len("SONGWRITER "):])
 			if currentTrack != nil {
@@ -196,7 +182,6 @@ func ParseCueFile(cuePath string) (*CueSheet, error) {
 		}
 	}

-	// Don't forget the last track
 	if currentTrack != nil {
 		sheet.Tracks = append(sheet.Tracks, *currentTrack)
 	}
@@ -212,7 +197,6 @@ func ParseCueFile(cuePath string) (*CueSheet, error) {
 	return sheet, nil
 }

-// parseCueTimestamp converts MM:SS:FF (frames at 75fps) to seconds
 func parseCueTimestamp(ts string) float64 {
 	parts := strings.Split(ts, ":")
 	if len(parts) != 3 {
@@ -226,7 +210,6 @@ func parseCueTimestamp(ts string) float64 {
 	return float64(minutes)*60 + float64(seconds) + float64(frames)/75.0
 }

-// formatCueTimestamp converts seconds to HH:MM:SS.mmm format for FFmpeg
 func formatCueTimestamp(seconds float64) string {
 	if seconds < 0 {
 		return "0"
@@ -237,7 +220,6 @@ func formatCueTimestamp(seconds float64) string {
 	return fmt.Sprintf("%02d:%02d:%06.3f", hours, mins, secs)
 }

-// unquoteCue removes surrounding quotes from a CUE value
 func unquoteCue(s string) string {
 	s = strings.TrimSpace(s)
 	if matches := reQuoted.FindStringSubmatch(s); len(matches) == 2 {
@@ -246,14 +228,12 @@ func unquoteCue(s string) string {
 	return s
 }

-// parseCueFileLine parses the FILE command's filename and type
 func parseCueFileLine(rest string) (string, string) {
 	rest = strings.TrimSpace(rest)

 	var filename, ftype string

 	if strings.HasPrefix(rest, "\"") {
-		// Quoted filename
 		endQuote := strings.Index(rest[1:], "\"")
 		if endQuote >= 0 {
 			filename = rest[1 : endQuote+1]
@@ -263,7 +243,6 @@ func parseCueFileLine(rest string) (string, string) {
 			filename = rest
 		}
 	} else {
-		// Unquoted filename - last word is the type
 		parts := strings.Fields(rest)
 		if len(parts) >= 2 {
 			ftype = parts[len(parts)-1]
@@ -276,33 +255,27 @@ func parseCueFileLine(rest string) (string, string) {
 	return filename, strings.TrimSpace(ftype)
 }

-// ResolveCueAudioPath finds the actual audio file referenced by a .cue sheet.
-// It checks relative to the cue file's directory.
 func ResolveCueAudioPath(cuePath string, cueFileName string) string {
 	cueDir := filepath.Dir(cuePath)

-	// 1. Try the exact filename from the .cue
 	candidate := filepath.Join(cueDir, cueFileName)
 	if _, err := os.Stat(candidate); err == nil {
 		return candidate
 	}

-	// 2. Try common case variations
 	baseName := strings.TrimSuffix(cueFileName, filepath.Ext(cueFileName))
-	commonExts := []string{".flac", ".wav", ".ape", ".mp3", ".ogg", ".wv", ".m4a"}
+	commonExts := []string{".flac", ".wav", ".aiff", ".aif", ".ape", ".mp3", ".ogg", ".wv", ".m4a"}
 	for _, ext := range commonExts {
 		candidate = filepath.Join(cueDir, baseName+ext)
 		if _, err := os.Stat(candidate); err == nil {
 			return candidate
 		}
-		// Try uppercase ext
 		candidate = filepath.Join(cueDir, baseName+strings.ToUpper(ext))
 		if _, err := os.Stat(candidate); err == nil {
 			return candidate
 		}
 	}

-	// 3. Try to find any audio file with the same base name as the .cue file
 	cueBase := strings.TrimSuffix(filepath.Base(cuePath), filepath.Ext(cuePath))
 	for _, ext := range commonExts {
 		candidate = filepath.Join(cueDir, cueBase+ext)
@@ -311,7 +284,6 @@ func ResolveCueAudioPath(cuePath string, cueFileName string) string {
 		}
 	}

-	// 4. If there's only one audio file in the directory, use that
 	entries, err := os.ReadDir(cueDir)
 	if err == nil {
 		audioExts := map[string]bool{
@@ -336,13 +308,9 @@ func ResolveCueAudioPath(cuePath string, cueFileName string) string {
 	return ""
 }

-// BuildCueSplitInfo creates the split information from a parsed CUE sheet.
-// This is returned to the Dart side so FFmpeg can perform the splitting.
-// audioDir, if non-empty, overrides the directory for audio file resolution.
 func BuildCueSplitInfo(cuePath string, sheet *CueSheet, audioDir string) (*CueSplitInfo, error) {
 	resolveDir := cuePath
 	if audioDir != "" {
-		// Create a virtual path in audioDir so ResolveCueAudioPath looks there
 		resolveDir = filepath.Join(audioDir, filepath.Base(cuePath))
 	}
 	audioPath := ResolveCueAudioPath(resolveDir, sheet.FileName)
@@ -370,11 +338,9 @@ func BuildCueSplitInfo(cuePath string, sheet *CueSheet, audioDir string) (*CueSp
 			composer = sheet.Composer
 		}

-		// End time is the start of the next track, or -1 for the last track
 		endSec := float64(-1)
 		if i+1 < len(sheet.Tracks) {
 			nextTrack := sheet.Tracks[i+1]
-			// Use pre-gap of next track if available, otherwise its start time
 			if nextTrack.PreGap >= 0 {
 				endSec = nextTrack.PreGap
 			} else {
@@ -396,11 +362,6 @@ func BuildCueSplitInfo(cuePath string, sheet *CueSheet, audioDir string) (*CueSp
 	return info, nil
 }

-// ParseCueFileJSON parses a .cue file and returns JSON with split info.
-// This is the main entry point called from Dart via the platform bridge.
-// audioDir, if non-empty, overrides the directory used for resolving the
-// referenced audio file (useful when the .cue was copied to a temp dir
-// but the audio still lives in the original location, e.g. SAF).
 func ParseCueFileJSON(cuePath string, audioDir string) (string, error) {
 	sheet, err := ParseCueFile(cuePath)
 	if err != nil {
@@ -420,9 +381,6 @@ func ParseCueFileJSON(cuePath string, audioDir string) (string, error) {
 	return string(jsonBytes), nil
 }

-// ScanCueFileForLibrary parses a .cue file and returns multiple LibraryScanResult
-// entries, one per track. This is used by the library scanner to populate the
-// library with individual track entries from a single CUE+FLAC album.
 func ScanCueFileForLibrary(cuePath string, scanTime string) ([]LibraryScanResult, error) {
 	sheet, err := ParseCueFile(cuePath)
 	if err != nil {
@@ -432,17 +390,21 @@ func ScanCueFileForLibrary(cuePath string, scanTime string) ([]LibraryScanResult
 	if err != nil {
 		return nil, err
 	}
-	return scanCueSheetForLibrary(cuePath, sheet, audioPath, "", 0, scanTime)
+	return scanCueSheetForLibrary(cuePath, sheet, audioPath, "", 0, "", scanTime)
 }

-// ScanCueFileForLibraryExt is like ScanCueFileForLibrary but with extra parameters
-// for SAF (Storage Access Framework) scenarios:
-//   - audioDir: if non-empty, overrides the directory used to find the audio file
-//   - virtualPathPrefix: if non-empty, used instead of cuePath as the base for
-//     virtual file paths (e.g. a content:// URI). IDs are also based on this.
-//   - fileModTime: if > 0, used as the FileModTime for all results instead of
-//     stat-ing the cuePath on disk (useful when the real file lives behind SAF)
 func ScanCueFileForLibraryExt(cuePath, audioDir, virtualPathPrefix string, fileModTime int64, scanTime string) ([]LibraryScanResult, error) {
+	return ScanCueFileForLibraryExtWithCoverCacheKey(
+		cuePath,
+		audioDir,
+		virtualPathPrefix,
+		fileModTime,
+		"",
+		scanTime,
+	)
+}
+
+func ScanCueFileForLibraryExtWithCoverCacheKey(cuePath, audioDir, virtualPathPrefix string, fileModTime int64, coverCacheKey, scanTime string) ([]LibraryScanResult, error) {
 	sheet, err := ParseCueFile(cuePath)
 	if err != nil {
 		return nil, err
@@ -451,7 +413,15 @@ func ScanCueFileForLibraryExt(cuePath, audioDir, virtualPathPrefix string, fileM
 	if err != nil {
 		return nil, err
 	}
-	return scanCueSheetForLibrary(cuePath, sheet, audioPath, virtualPathPrefix, fileModTime, scanTime)
+	return scanCueSheetForLibrary(
+		cuePath,
+		sheet,
+		audioPath,
+		virtualPathPrefix,
+		fileModTime,
+		coverCacheKey,
+		scanTime,
+	)
 }

 func resolveCueAudioPathForLibrary(cuePath string, sheet *CueSheet, audioDir string) (string, error) {
@@ -469,12 +439,11 @@ func resolveCueAudioPathForLibrary(cuePath string, sheet *CueSheet, audioDir str
 	return audioPath, nil
 }

-func scanCueSheetForLibrary(cuePath string, sheet *CueSheet, audioPath, virtualPathPrefix string, fileModTime int64, scanTime string) ([]LibraryScanResult, error) {
+func scanCueSheetForLibrary(cuePath string, sheet *CueSheet, audioPath, virtualPathPrefix string, fileModTime int64, coverCacheKey, scanTime string) ([]LibraryScanResult, error) {
 	if sheet == nil {
 		return nil, fmt.Errorf("cue sheet is nil for %s", cuePath)
 	}

-	// Try to get quality info from the audio file
 	var bitDepth, sampleRate int
 	var totalDurationSec float64
 	audioExt := strings.ToLower(filepath.Ext(audioPath))
@@ -496,25 +465,27 @@ func scanCueSheetForLibrary(cuePath string, sheet *CueSheet, audioPath, virtualP
 		}
 	}

-	// Extract cover from audio file for all tracks
 	var coverPath string
 	libraryCoverCacheMu.RLock()
 	coverCacheDir := libraryCoverCacheDir
 	libraryCoverCacheMu.RUnlock()
 	if coverCacheDir != "" {
-		cp, err := SaveCoverToCache(audioPath, coverCacheDir)
+		cp, err := SaveCoverToCacheWithHintAndKey(
+			audioPath,
+			"",
+			coverCacheDir,
+			coverCacheKey,
+		)
 		if err == nil && cp != "" {
 			coverPath = cp
 		}
 	}

-	// Determine the base path for virtual paths and IDs
 	pathBase := cuePath
 	if virtualPathPrefix != "" {
 		pathBase = virtualPathPrefix
 	}

-	// Determine fileModTime
 	modTime := fileModTime
 	if modTime <= 0 {
 		if info, err := os.Stat(cuePath); err == nil {
@@ -542,7 +513,11 @@ func scanCueSheetForLibrary(cuePath string, sheet *CueSheet, audioPath, virtualP
 			album = "Unknown Album"
 		}

-		// Calculate duration for this track
+		composer := track.Composer
+		if composer == "" {
+			composer = sheet.Composer
+		}
+
 		var duration int
 		if i+1 < len(sheet.Tracks) {
 			nextStart := sheet.Tracks[i+1].StartTime
@@ -556,9 +531,6 @@ func scanCueSheetForLibrary(cuePath string, sheet *CueSheet, audioPath, virtualP

 		id := generateLibraryID(fmt.Sprintf("%s#track%d", pathBase, track.Number))

-		// Use a virtual file path that includes the track number to ensure
-		// uniqueness in the database (file_path has a UNIQUE constraint).
-		// Format: /path/to/album.cue#track01 or content://...album.cue#track01
 		virtualFilePath := fmt.Sprintf("%s#track%02d", pathBase, track.Number)

 		result := LibraryScanResult{
@@ -572,12 +544,15 @@ func scanCueSheetForLibrary(cuePath string, sheet *CueSheet, audioPath, virtualP
 			ScannedAt:   scanTime,
 			ISRC:        track.ISRC,
 			TrackNumber: track.Number,
+			TotalTracks: len(sheet.Tracks),
 			DiscNumber:  1,
+			TotalDiscs:  1,
 			Duration:    duration,
 			ReleaseDate: sheet.Date,
 			BitDepth:    bitDepth,
 			SampleRate:  sampleRate,
 			Genre:       sheet.Genre,
+			Composer:    composer,
 			Format:      "cue+" + strings.TrimPrefix(audioExt, "."),
 		}

@@ -196,15 +196,22 @@ type deezerAlbumSimple struct {
 	RecordType  string `json:"record_type"`
 }

-func (c *DeezerClient) convertTrack(track deezerTrack) TrackMetadata {
-	artistName := track.Artist.Name
+// deezerTrackArtistDisplay returns the display artist string for a track,
+// preferring the Contributors list (comma-joined) when available, falling
+// back to the primary Artist.Name.
+func deezerTrackArtistDisplay(track deezerTrack) string {
 	if len(track.Contributors) > 0 {
 		names := make([]string, len(track.Contributors))
 		for i, a := range track.Contributors {
 			names[i] = a.Name
 		}
-		artistName = strings.Join(names, ", ")
+		return strings.Join(names, ", ")
 	}
+	return track.Artist.Name
+}
+
+func (c *DeezerClient) convertTrack(track deezerTrack) TrackMetadata {
+	artistName := deezerTrackArtistDisplay(track)

 	albumImage := track.Album.CoverXL
 	if albumImage == "" {
@@ -623,6 +630,12 @@ func (c *DeezerClient) GetAlbum(ctx context.Context, albumID string) (*AlbumResp
 	}

 	isrcMap := c.fetchISRCsParallel(ctx, allTracks)
+	totalDiscs := 0
+	for _, track := range allTracks {
+		if track.DiskNumber > totalDiscs {
+			totalDiscs = track.DiskNumber
+		}
+	}

 	tracks := make([]AlbumTrackMetadata, 0, len(allTracks))
 	albumType := album.RecordType
@@ -641,7 +654,7 @@ func (c *DeezerClient) GetAlbum(ctx context.Context, albumID string) (*AlbumResp

 		tracks = append(tracks, AlbumTrackMetadata{
 			SpotifyID:   fmt.Sprintf("deezer:%d", track.ID),
-			Artists:     track.Artist.Name,
+			Artists:     deezerTrackArtistDisplay(track),
 			Name:        track.Title,
 			AlbumName:   album.Title,
 			AlbumArtist: artistName,
@@ -651,6 +664,7 @@ func (c *DeezerClient) GetAlbum(ctx context.Context, albumID string) (*AlbumResp
 			TrackNumber: trackNum,
 			TotalTracks: album.NbTracks,
 			DiscNumber:  track.DiskNumber,
+			TotalDiscs:  totalDiscs,
 			ExternalURL: track.Link,
 			ISRC:        isrc,
 			AlbumID:     fmt.Sprintf("deezer:%d", album.ID),
@@ -741,6 +755,10 @@ func (c *DeezerClient) GetArtist(ctx context.Context, artistID string) (*ArtistR
 				Artists:     artist.Name,
 			})
 		}
+
+		// The Deezer /artist/{id}/albums endpoint does not return nb_tracks.
+		// Fetch track counts in parallel from individual /album/{id} endpoints.
+		c.fetchAlbumTrackCounts(ctx, albums)
 	}

 	result := &ArtistResponsePayload{
@@ -760,6 +778,63 @@ func (c *DeezerClient) GetArtist(ctx context.Context, artistID string) (*ArtistR
 	return result, nil
 }

+// fetchAlbumTrackCounts fetches nb_tracks for each album in parallel using
+// individual /album/{id} calls, since the /artist/{id}/albums endpoint does
+// not include this field. Albums whose track count is already known (non-zero)
+// are skipped.
+func (c *DeezerClient) fetchAlbumTrackCounts(ctx context.Context, albums []ArtistAlbumMetadata) {
+	// Find albums that need track counts
+	type indexedID struct {
+		idx     int
+		albumID string
+	}
+	var toFetch []indexedID
+	for i, a := range albums {
+		if a.TotalTracks == 0 {
+			rawID := strings.TrimPrefix(a.ID, "deezer:")
+			if rawID != "" {
+				toFetch = append(toFetch, indexedID{idx: i, albumID: rawID})
+			}
+		}
+	}
+	if len(toFetch) == 0 {
+		return
+	}
+
+	const maxParallel = 10
+	sem := make(chan struct{}, maxParallel)
+	var mu sync.Mutex
+	var wg sync.WaitGroup
+
+	for _, item := range toFetch {
+		wg.Add(1)
+		go func(it indexedID) {
+			defer wg.Done()
+
+			select {
+			case sem <- struct{}{}:
+				defer func() { <-sem }()
+			case <-ctx.Done():
+				return
+			}
+
+			albumURL := fmt.Sprintf(deezerAlbumURL, it.albumID)
+			var resp struct {
+				NbTracks int `json:"nb_tracks"`
+			}
+			if err := c.getJSON(ctx, albumURL, &resp); err != nil {
+				return
+			}
+
+			mu.Lock()
+			albums[it.idx].TotalTracks = resp.NbTracks
+			mu.Unlock()
+		}(item)
+	}
+
+	wg.Wait()
+}
+
 func (c *DeezerClient) GetRelatedArtists(ctx context.Context, artistID string, limit int) ([]SearchArtistResult, error) {
 	normalizedArtistID := strings.TrimSpace(strings.TrimPrefix(artistID, "deezer:"))
 	if normalizedArtistID == "" {
@@ -892,7 +967,7 @@ func (c *DeezerClient) GetPlaylist(ctx context.Context, playlistID string) (*Pla

 		tracks = append(tracks, AlbumTrackMetadata{
 			SpotifyID:   fmt.Sprintf("deezer:%d", track.ID),
-			Artists:     track.Artist.Name,
+			Artists:     deezerTrackArtistDisplay(track),
 			Name:        track.Title,
 			AlbumName:   track.Album.Title,
 			AlbumArtist: track.Artist.Name,
@@ -1181,7 +1256,7 @@ func (c *DeezerClient) getJSON(ctx context.Context, endpoint string, dst interfa

 	for attempt := 0; attempt <= deezerMaxRetries; attempt++ {
 		if attempt > 0 {
-			delay := deezerRetryDelay * time.Duration(1<<(attempt-1)) // Exponential backoff
+			delay := deezerRetryDelay * time.Duration(1<<(attempt-1))
 			GoLog("[Deezer] Retry %d/%d after %v...\n", attempt, deezerMaxRetries, delay)
 			time.Sleep(delay)
 		}
@@ -1194,7 +1269,6 @@ func (c *DeezerClient) getJSON(ctx context.Context, endpoint string, dst interfa
 		lastErr = err
 		errStr := err.Error()

-		// Check if error is retryable
 		isRetryable := strings.Contains(errStr, "timeout") ||
 			strings.Contains(errStr, "connection reset") ||
 			strings.Contains(errStr, "connection refused") ||
@@ -1,606 +0,0 @@
-package gobackend
-
-import (
-	"bufio"
-	"bytes"
-	"context"
-	"encoding/json"
-	"errors"
-	"fmt"
-	"io"
-	"net/http"
-	"os"
-	"path/filepath"
-	"strings"
-)
-
-const deezerYoinkifyURL = "https://yoinkify.lol/api/download"
-const deezerMusicDLURL = "https://www.musicdl.me/api/download"
-
-type YoinkifyRequest struct {
-	URL         string `json:"url"`
-	Format      string `json:"format"`
-	GenreSource string `json:"genreSource"`
-}
-
-type DeezerDownloadResult struct {
-	FilePath    string
-	BitDepth    int
-	SampleRate  int
-	Title       string
-	Artist      string
-	Album       string
-	ReleaseDate string
-	TrackNumber int
-	DiscNumber  int
-	ISRC        string
-	LyricsLRC   string
-}
-
-func resolveSpotifyURLForYoinkify(req DownloadRequest) (string, error) {
-	rawSpotify := strings.TrimSpace(req.SpotifyID)
-	if rawSpotify != "" {
-		if isLikelySpotifyTrackID(rawSpotify) {
-			return fmt.Sprintf("https://open.spotify.com/track/%s", rawSpotify), nil
-		}
-
-		if parsed, err := parseSpotifyURI(rawSpotify); err == nil && parsed.Type == "track" && parsed.ID != "" {
-			return fmt.Sprintf("https://open.spotify.com/track/%s", parsed.ID), nil
-		}
-	}
-
-	deezerID := strings.TrimSpace(req.DeezerID)
-	if deezerID == "" {
-		if prefixed, found := strings.CutPrefix(rawSpotify, "deezer:"); found {
-			deezerID = strings.TrimSpace(prefixed)
-		}
-	}
-
-	if deezerID != "" {
-		songlink := NewSongLinkClient()
-		spotifyID, err := songlink.GetSpotifyIDFromDeezer(deezerID)
-		if err != nil {
-			return "", fmt.Errorf("failed to map deezer:%s to Spotify ID: %w", deezerID, err)
-		}
-		spotifyID = strings.TrimSpace(spotifyID)
-		if spotifyID == "" {
-			return "", fmt.Errorf("SongLink returned empty Spotify ID for deezer:%s", deezerID)
-		}
-		return fmt.Sprintf("https://open.spotify.com/track/%s", spotifyID), nil
-	}
-
-	return "", fmt.Errorf("missing Spotify track ID for Deezer Yoinkify")
-}
-
-func isLikelySpotifyTrackID(value string) bool {
-	if len(value) != 22 {
-		return false
-	}
-	for _, r := range value {
-		switch {
-		case r >= 'A' && r <= 'Z':
-		case r >= 'a' && r <= 'z':
-		case r >= '0' && r <= '9':
-		default:
-			return false
-		}
-	}
-	return true
-}
-
-func (c *DeezerClient) DownloadFromYoinkify(spotifyURL, outputPath string, outputFD int, itemID string) error {
-	payload := YoinkifyRequest{
-		URL:         spotifyURL,
-		Format:      "flac",
-		GenreSource: "spotify",
-	}
-
-	jsonData, err := json.Marshal(payload)
-	if err != nil {
-		return fmt.Errorf("failed to encode Yoinkify request: %w", err)
-	}
-
-	ctx := context.Background()
-	if itemID != "" {
-		StartItemProgress(itemID)
-		defer CompleteItemProgress(itemID)
-		ctx = initDownloadCancel(itemID)
-		defer clearDownloadCancel(itemID)
-	}
-
-	if isDownloadCancelled(itemID) {
-		return ErrDownloadCancelled
-	}
-
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, deezerYoinkifyURL, bytes.NewBuffer(jsonData))
-	if err != nil {
-		return fmt.Errorf("failed to create Yoinkify request: %w", err)
-	}
-	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("Accept", "*/*")
-	req.Header.Set("User-Agent", getRandomUserAgent())
-
-	resp, err := GetDownloadClient().Do(req)
-	if err != nil {
-		if isDownloadCancelled(itemID) {
-			return ErrDownloadCancelled
-		}
-		return fmt.Errorf("failed to call Yoinkify: %w", err)
-	}
-	defer resp.Body.Close()
-
-	contentType := strings.ToLower(strings.TrimSpace(resp.Header.Get("Content-Type")))
-	if resp.StatusCode != http.StatusOK {
-		bodyBytes, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
-		bodyText := strings.TrimSpace(string(bodyBytes))
-		if bodyText != "" {
-			return fmt.Errorf("Yoinkify returned status %d: %s", resp.StatusCode, bodyText)
-		}
-		return fmt.Errorf("Yoinkify returned status %d", resp.StatusCode)
-	}
-
-	if strings.Contains(contentType, "application/json") {
-		bodyBytes, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
-		bodyText := strings.TrimSpace(string(bodyBytes))
-		if bodyText == "" {
-			bodyText = "empty JSON payload"
-		}
-		return fmt.Errorf("Yoinkify returned JSON instead of audio: %s", bodyText)
-	}
-
-	expectedSize := resp.ContentLength
-	if expectedSize > 0 && itemID != "" {
-		SetItemBytesTotal(itemID, expectedSize)
-	}
-
-	out, err := openOutputForWrite(outputPath, outputFD)
-	if err != nil {
-		return err
-	}
-
-	bufWriter := bufio.NewWriterSize(out, 256*1024)
-	var written int64
-	if itemID != "" {
-		pw := NewItemProgressWriter(bufWriter, itemID)
-		written, err = io.Copy(pw, resp.Body)
-	} else {
-		written, err = io.Copy(bufWriter, resp.Body)
-	}
-
-	flushErr := bufWriter.Flush()
-	closeErr := out.Close()
-
-	if err != nil {
-		cleanupOutputOnError(outputPath, outputFD)
-		if isDownloadCancelled(itemID) {
-			return ErrDownloadCancelled
-		}
-		return fmt.Errorf("download interrupted: %w", err)
-	}
-	if flushErr != nil {
-		cleanupOutputOnError(outputPath, outputFD)
-		return fmt.Errorf("failed to flush output: %w", flushErr)
-	}
-	if closeErr != nil {
-		cleanupOutputOnError(outputPath, outputFD)
-		return fmt.Errorf("failed to close output: %w", closeErr)
-	}
-
-	if expectedSize > 0 && written != expectedSize {
-		cleanupOutputOnError(outputPath, outputFD)
-		return fmt.Errorf("incomplete download: expected %d bytes, got %d bytes", expectedSize, written)
-	}
-
-	GoLog("[Deezer] Downloaded via Yoinkify: %.2f MB\n", float64(written)/(1024*1024))
-	return nil
-}
-
-func resolveDeezerTrackURL(req DownloadRequest) (string, error) {
-	deezerID := strings.TrimSpace(req.DeezerID)
-	if deezerID == "" {
-		if prefixed, found := strings.CutPrefix(strings.TrimSpace(req.SpotifyID), "deezer:"); found {
-			deezerID = strings.TrimSpace(prefixed)
-		}
-	}
-	if deezerID != "" {
-		trackURL := fmt.Sprintf("https://www.deezer.com/track/%s", deezerID)
-		if err := verifyDeezerTrack(req, deezerID); err != nil {
-			GoLog("[Deezer] Direct ID %s verification failed: %v\n", deezerID, err)
-			// Don't reject direct IDs from request payload — they're presumably correct.
-		}
-		return trackURL, nil
-	}
-
-	// Try SongLink
-	spotifyID := strings.TrimSpace(req.SpotifyID)
-	if spotifyID != "" && isLikelySpotifyTrackID(spotifyID) {
-		songlink := NewSongLinkClient()
-		availability, err := songlink.CheckTrackAvailability(spotifyID, "")
-		if err == nil && availability.Deezer && availability.DeezerURL != "" {
-			resolvedID := extractDeezerIDFromURL(availability.DeezerURL)
-			if resolvedID != "" {
-				if verifyErr := verifyDeezerTrack(req, resolvedID); verifyErr != nil {
-					GoLog("[Deezer] SongLink ID %s rejected: %v\n", resolvedID, verifyErr)
-					// Fall through to ISRC search instead of using wrong track.
-				} else {
-					return availability.DeezerURL, nil
-				}
-			} else {
-				return availability.DeezerURL, nil
-			}
-		}
-	}
-
-	// Try ISRC
-	isrc := strings.TrimSpace(req.ISRC)
-	if isrc != "" {
-		ctx, cancel := context.WithTimeout(context.Background(), SongLinkTimeout)
-		defer cancel()
-		track, err := GetDeezerClient().SearchByISRC(ctx, isrc)
-		if err == nil && track != nil {
-			resolvedID := songLinkExtractDeezerTrackID(track)
-			if resolvedID != "" {
-				if verifyErr := verifyDeezerTrack(req, resolvedID); verifyErr != nil {
-					GoLog("[Deezer] ISRC-resolved ID %s rejected: %v\n", resolvedID, verifyErr)
-					return "", fmt.Errorf("deezer track resolved via ISRC does not match: %w", verifyErr)
-				}
-				return fmt.Sprintf("https://www.deezer.com/track/%s", resolvedID), nil
-			}
-		}
-	}
-
-	return "", fmt.Errorf("could not resolve Deezer track URL")
-}
-
-func verifyDeezerTrack(req DownloadRequest, deezerID string) error {
-	ctx, cancel := context.WithTimeout(context.Background(), SongLinkTimeout)
-	defer cancel()
-	trackResp, err := GetDeezerClient().GetTrack(ctx, deezerID)
-	if err != nil {
-		return nil // Can't verify — don't block the download.
-	}
-	resolved := resolvedTrackInfo{
-		Title:      trackResp.Track.Name,
-		ArtistName: trackResp.Track.Artists,
-		Duration:   trackResp.Track.DurationMS / 1000,
-	}
-	if !trackMatchesRequest(req, resolved, "Deezer") {
-		return fmt.Errorf("expected '%s - %s', got '%s - %s'",
-			req.ArtistName, req.TrackName, resolved.ArtistName, resolved.Title)
-	}
-	GoLog("[Deezer] Track %s verified: '%s - %s' ✓\n", deezerID, resolved.ArtistName, resolved.Title)
-	return nil
-}
-
-type deezerMusicDLRequest struct {
-	Platform string `json:"platform"`
-	URL      string `json:"url"`
-}
-
-func (c *DeezerClient) GetMusicDLDownloadURL(deezerTrackURL string) (string, error) {
-	payload := deezerMusicDLRequest{
-		Platform: "deezer",
-		URL:      deezerTrackURL,
-	}
-	jsonData, err := json.Marshal(payload)
-	if err != nil {
-		return "", fmt.Errorf("failed to encode MusicDL request: %w", err)
-	}
-
-	req, err := http.NewRequest(http.MethodPost, deezerMusicDLURL, bytes.NewReader(jsonData))
-	if err != nil {
-		return "", fmt.Errorf("failed to create MusicDL request: %w", err)
-	}
-	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("X-Debug-Key", getQobuzDebugKey())
-	req.Header.Set("User-Agent", getRandomUserAgent())
-
-	resp, err := c.httpClient.Do(req)
-	if err != nil {
-		return "", fmt.Errorf("MusicDL request failed: %w", err)
-	}
-	defer resp.Body.Close()
-
-	body, err := io.ReadAll(io.LimitReader(resp.Body, 64*1024))
-	if err != nil {
-		return "", fmt.Errorf("failed to read MusicDL response: %w", err)
-	}
-
-	if resp.StatusCode != http.StatusOK {
-		return "", fmt.Errorf("MusicDL returned HTTP %d: %s", resp.StatusCode, strings.TrimSpace(string(body)))
-	}
-
-	var raw map[string]any
-	if err := json.Unmarshal(body, &raw); err != nil {
-		return "", fmt.Errorf("invalid MusicDL JSON: %w", err)
-	}
-
-	if errMsg, ok := raw["error"].(string); ok && strings.TrimSpace(errMsg) != "" {
-		return "", fmt.Errorf("MusicDL error: %s", errMsg)
-	}
-
-	// Try various response fields for download URL
-	for _, key := range []string{"download_url", "url", "link"} {
-		if urlVal, ok := raw[key].(string); ok && strings.TrimSpace(urlVal) != "" {
-			return strings.TrimSpace(urlVal), nil
-		}
-	}
-	if data, ok := raw["data"].(map[string]any); ok {
-		for _, key := range []string{"download_url", "url", "link"} {
-			if urlVal, ok := data[key].(string); ok && strings.TrimSpace(urlVal) != "" {
-				return strings.TrimSpace(urlVal), nil
-			}
-		}
-	}
-
-	return "", fmt.Errorf("no download URL found in MusicDL response")
-}
-
-func (c *DeezerClient) DownloadFromMusicDL(deezerTrackURL, outputPath string, outputFD int, itemID string) error {
-	GoLog("[Deezer] Resolving download URL via MusicDL for: %s\n", deezerTrackURL)
-
-	downloadURL, err := c.GetMusicDLDownloadURL(deezerTrackURL)
-	if err != nil {
-		return err
-	}
-	GoLog("[Deezer] MusicDL returned download URL, starting download...\n")
-
-	ctx := context.Background()
-	if itemID != "" {
-		StartItemProgress(itemID)
-		defer CompleteItemProgress(itemID)
-		ctx = initDownloadCancel(itemID)
-		defer clearDownloadCancel(itemID)
-	}
-
-	if isDownloadCancelled(itemID) {
-		return ErrDownloadCancelled
-	}
-
-	req, err := http.NewRequestWithContext(ctx, "GET", downloadURL, nil)
-	if err != nil {
-		return fmt.Errorf("failed to create download request: %w", err)
-	}
-	req.Header.Set("User-Agent", getRandomUserAgent())
-
-	resp, err := GetDownloadClient().Do(req)
-	if err != nil {
-		if isDownloadCancelled(itemID) {
-			return ErrDownloadCancelled
-		}
-		return fmt.Errorf("download request failed: %w", err)
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode != http.StatusOK {
-		return fmt.Errorf("download returned HTTP %d", resp.StatusCode)
-	}
-
-	expectedSize := resp.ContentLength
-	if expectedSize > 0 && itemID != "" {
-		SetItemBytesTotal(itemID, expectedSize)
-	}
-
-	out, err := openOutputForWrite(outputPath, outputFD)
-	if err != nil {
-		return err
-	}
-
-	bufWriter := bufio.NewWriterSize(out, 256*1024)
-	var written int64
-	if itemID != "" {
-		pw := NewItemProgressWriter(bufWriter, itemID)
-		written, err = io.Copy(pw, resp.Body)
-	} else {
-		written, err = io.Copy(bufWriter, resp.Body)
-	}
-
-	flushErr := bufWriter.Flush()
-	closeErr := out.Close()
-
-	if err != nil {
-		cleanupOutputOnError(outputPath, outputFD)
-		if isDownloadCancelled(itemID) {
-			return ErrDownloadCancelled
-		}
-		return fmt.Errorf("download interrupted: %w", err)
-	}
-	if flushErr != nil {
-		cleanupOutputOnError(outputPath, outputFD)
-		return fmt.Errorf("failed to flush output: %w", flushErr)
-	}
-	if closeErr != nil {
-		cleanupOutputOnError(outputPath, outputFD)
-		return fmt.Errorf("failed to close output: %w", closeErr)
-	}
-
-	if expectedSize > 0 && written != expectedSize {
-		cleanupOutputOnError(outputPath, outputFD)
-		return fmt.Errorf("incomplete download: expected %d bytes, got %d bytes", expectedSize, written)
-	}
-
-	GoLog("[Deezer] Downloaded via MusicDL: %.2f MB\n", float64(written)/(1024*1024))
-	return nil
-}
-
-func downloadFromDeezer(req DownloadRequest) (DeezerDownloadResult, error) {
-	deezerClient := GetDeezerClient()
-	isSafOutput := isFDOutput(req.OutputFD) || strings.TrimSpace(req.OutputPath) != ""
-
-	if !isSafOutput {
-		if existingFile, exists := checkISRCExistsInternal(req.OutputDir, req.ISRC); exists {
-			return DeezerDownloadResult{FilePath: "EXISTS:" + existingFile}, nil
-		}
-	}
-
-	filename := buildFilenameFromTemplate(req.FilenameFormat, map[string]interface{}{
-		"title":  req.TrackName,
-		"artist": req.ArtistName,
-		"album":  req.AlbumName,
-		"track":  req.TrackNumber,
-		"year":   extractYear(req.ReleaseDate),
-		"date":   req.ReleaseDate,
-		"disc":   req.DiscNumber,
-	})
-
-	var outputPath string
-	if isSafOutput {
-		outputPath = strings.TrimSpace(req.OutputPath)
-		if outputPath == "" && isFDOutput(req.OutputFD) {
-			outputPath = fmt.Sprintf("/proc/self/fd/%d", req.OutputFD)
-		}
-	} else {
-		filename = sanitizeFilename(filename) + ".flac"
-		outputPath = filepath.Join(req.OutputDir, filename)
-		if fileInfo, statErr := os.Stat(outputPath); statErr == nil && fileInfo.Size() > 0 {
-			return DeezerDownloadResult{FilePath: "EXISTS:" + outputPath}, nil
-		}
-	}
-
-	var parallelResult *ParallelDownloadResult
-	parallelDone := make(chan struct{})
-	go func() {
-		defer close(parallelDone)
-		coverURL := req.CoverURL
-		embedLyrics := req.EmbedLyrics
-		if !req.EmbedMetadata {
-			coverURL = ""
-			embedLyrics = false
-		}
-		parallelResult = FetchCoverAndLyricsParallel(
-			coverURL,
-			req.EmbedMaxQualityCover,
-			req.SpotifyID,
-			req.TrackName,
-			req.ArtistName,
-			embedLyrics,
-			int64(req.DurationMS),
-		)
-	}()
-
-	// Try MusicDL first (better quality), fallback to Yoinkify
-	var downloadErr error
-	deezerTrackURL, deezerURLErr := resolveDeezerTrackURL(req)
-	if deezerURLErr == nil {
-		GoLog("[Deezer] Trying MusicDL for: %s\n", deezerTrackURL)
-		downloadErr = deezerClient.DownloadFromMusicDL(deezerTrackURL, outputPath, req.OutputFD, req.ItemID)
-		if downloadErr != nil {
-			if errors.Is(downloadErr, ErrDownloadCancelled) {
-				return DeezerDownloadResult{}, ErrDownloadCancelled
-			}
-			GoLog("[Deezer] MusicDL failed: %v, falling back to Yoinkify\n", downloadErr)
-		}
-	} else {
-		GoLog("[Deezer] Could not resolve Deezer URL: %v, using Yoinkify directly\n", deezerURLErr)
-	}
-
-	if downloadErr != nil || deezerURLErr != nil {
-		spotifyURL, err := resolveSpotifyURLForYoinkify(req)
-		if err != nil {
-			if deezerURLErr != nil {
-				return DeezerDownloadResult{}, fmt.Errorf(
-					"deezer download failed: direct Deezer resolution error: %v; Yoinkify fallback error: %w",
-					deezerURLErr,
-					err,
-				)
-			}
-			return DeezerDownloadResult{}, err
-		}
-		downloadErr = deezerClient.DownloadFromYoinkify(spotifyURL, outputPath, req.OutputFD, req.ItemID)
-		if downloadErr != nil {
-			if errors.Is(downloadErr, ErrDownloadCancelled) {
-				return DeezerDownloadResult{}, ErrDownloadCancelled
-			}
-			return DeezerDownloadResult{}, fmt.Errorf("deezer download failed (MusicDL + Yoinkify): %w", downloadErr)
-		}
-	}
-
-	<-parallelDone
-
-	if req.ItemID != "" {
-		SetItemProgress(req.ItemID, 1.0, 0, 0)
-		SetItemFinalizing(req.ItemID)
-	}
-
-	metadata := Metadata{
-		Title:       req.TrackName,
-		Artist:      req.ArtistName,
-		Album:       req.AlbumName,
-		AlbumArtist: req.AlbumArtist,
-		Date:        req.ReleaseDate,
-		TrackNumber: req.TrackNumber,
-		TotalTracks: req.TotalTracks,
-		DiscNumber:  req.DiscNumber,
-		ISRC:        req.ISRC,
-		Genre:       req.Genre,
-		Label:       req.Label,
-		Copyright:   req.Copyright,
-	}
-
-	var coverData []byte
-	if parallelResult != nil && parallelResult.CoverData != nil {
-		coverData = parallelResult.CoverData
-	}
-
-	if isSafOutput || !req.EmbedMetadata {
-		if !req.EmbedMetadata {
-			GoLog("[Deezer] Metadata embedding disabled by settings, skipping in-backend metadata/lyrics embedding\n")
-		} else {
-			GoLog("[Deezer] SAF output detected - skipping in-backend metadata/lyrics embedding (handled in Flutter)\n")
-		}
-	} else {
-		if err := EmbedMetadataWithCoverData(outputPath, metadata, coverData); err != nil {
-			GoLog("[Deezer] Warning: failed to embed metadata: %v\n", err)
-		}
-
-		if req.EmbedLyrics && parallelResult != nil && parallelResult.LyricsLRC != "" {
-			lyricsMode := req.LyricsMode
-			if lyricsMode == "" {
-				lyricsMode = "embed"
-			}
-
-			if lyricsMode == "external" || lyricsMode == "both" {
-				if lrcPath, lrcErr := SaveLRCFile(outputPath, parallelResult.LyricsLRC); lrcErr != nil {
-					GoLog("[Deezer] Warning: failed to save LRC file: %v\n", lrcErr)
-				} else {
-					GoLog("[Deezer] LRC file saved: %s\n", lrcPath)
-				}
-			}
-
-			if lyricsMode == "embed" || lyricsMode == "both" {
-				if embedErr := EmbedLyrics(outputPath, parallelResult.LyricsLRC); embedErr != nil {
-					GoLog("[Deezer] Warning: failed to embed lyrics: %v\n", embedErr)
-				}
-			}
-		}
-	}
-
-	if !isSafOutput {
-		AddToISRCIndex(req.OutputDir, req.ISRC, outputPath)
-	}
-
-	bitDepth, sampleRate := 0, 0
-	if quality, qErr := GetAudioQuality(outputPath); qErr == nil {
-		bitDepth = quality.BitDepth
-		sampleRate = quality.SampleRate
-	}
-
-	lyricsLRC := ""
-	if req.EmbedMetadata && req.EmbedLyrics && parallelResult != nil && parallelResult.LyricsLRC != "" {
-		lyricsLRC = parallelResult.LyricsLRC
-	}
-
-	return DeezerDownloadResult{
-		FilePath:    outputPath,
-		BitDepth:    bitDepth,
-		SampleRate:  sampleRate,
-		Title:       req.TrackName,
-		Artist:      req.ArtistName,
-		Album:       req.AlbumName,
-		ReleaseDate: req.ReleaseDate,
-		TrackNumber: req.TrackNumber,
-		DiscNumber:  req.DiscNumber,
-		ISRC:        req.ISRC,
-		LyricsLRC:   lyricsLRC,
-	}, nil
-}
@@ -0,0 +1,153 @@
+package gobackend
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestDeezerClientWithFakeHTTP(t *testing.T) {
+	client := &DeezerClient{
+		httpClient: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			body := fakeDeezerResponse(req.URL.Path, req.URL.RawQuery)
+			status := http.StatusOK
+			if body == "" {
+				status = http.StatusNotFound
+				body = `{"error":"missing"}`
+			}
+			return &http.Response{
+				StatusCode: status,
+				Header:     make(http.Header),
+				Body:       io.NopCloser(strings.NewReader(body)),
+				Request:    req,
+			}, nil
+		})},
+		searchCache:          map[string]*cacheEntry{},
+		albumCache:           map[string]*cacheEntry{},
+		artistCache:          map[string]*cacheEntry{},
+		isrcCache:            map[string]string{},
+		cacheCleanupInterval: time.Millisecond,
+	}
+	ctx := context.Background()
+
+	search, err := client.SearchAll(ctx, "artist song", 2, 2, "")
+	if err != nil {
+		t.Fatalf("SearchAll: %v", err)
+	}
+	if len(search.Tracks) != 1 || len(search.Artists) != 1 || len(search.Albums) != 1 || len(search.Playlists) != 1 {
+		t.Fatalf("search = %#v", search)
+	}
+	cached, err := client.SearchAll(ctx, "artist song", 2, 2, "")
+	if err != nil || cached != search {
+		t.Fatalf("cached SearchAll = %#v/%v", cached, err)
+	}
+	if filtered, err := client.SearchAll(ctx, "artist song", 1, 1, "track"); err != nil || len(filtered.Tracks) != 1 || len(filtered.Artists) != 0 {
+		t.Fatalf("filtered search = %#v/%v", filtered, err)
+	}
+
+	track, err := client.GetTrack(ctx, "101")
+	if err != nil {
+		t.Fatalf("GetTrack: %v", err)
+	}
+	if track.Track.SpotifyID != "deezer:101" || track.Track.Artists != "Contributor A, Contributor B" {
+		t.Fatalf("track = %#v", track)
+	}
+
+	album, err := client.GetAlbum(ctx, "201")
+	if err != nil {
+		t.Fatalf("GetAlbum: %v", err)
+	}
+	if album.AlbumInfo.Name != "Album" || len(album.TrackList) != 2 || album.TrackList[1].ISRC == "" {
+		t.Fatalf("album = %#v", album)
+	}
+	if cachedAlbum, err := client.GetAlbum(ctx, "201"); err != nil || cachedAlbum != album {
+		t.Fatalf("cached album = %#v/%v", cachedAlbum, err)
+	}
+
+	artist, err := client.GetArtist(ctx, "301")
+	if err != nil {
+		t.Fatalf("GetArtist: %v", err)
+	}
+	if artist.ArtistInfo.Name != "Artist" || len(artist.Albums) != 1 || artist.Albums[0].TotalTracks == 0 {
+		t.Fatalf("artist = %#v", artist)
+	}
+	if cachedArtist, err := client.GetArtist(ctx, "301"); err != nil || cachedArtist != artist {
+		t.Fatalf("cached artist = %#v/%v", cachedArtist, err)
+	}
+
+	related, err := client.GetRelatedArtists(ctx, "deezer:301", 3)
+	if err != nil {
+		t.Fatalf("GetRelatedArtists: %v", err)
+	}
+	if len(related) != 1 || related[0].ID != "deezer:302" {
+		t.Fatalf("related = %#v", related)
+	}
+	if _, err := client.GetRelatedArtists(ctx, "", 0); err == nil {
+		t.Fatal("expected invalid related artist ID")
+	}
+
+	playlist, err := client.GetPlaylist(ctx, "401")
+	if err != nil {
+		t.Fatalf("GetPlaylist: %v", err)
+	}
+	if playlist.PlaylistInfo.Tracks.Total != 2 || len(playlist.TrackList) != 2 {
+		t.Fatalf("playlist = %#v", playlist)
+	}
+
+	byISRC, err := client.SearchByISRC(ctx, "USRC17607839")
+	if err != nil {
+		t.Fatalf("SearchByISRC: %v", err)
+	}
+	if byISRC.SpotifyID != "deezer:101" {
+		t.Fatalf("by ISRC = %#v", byISRC)
+	}
+	if _, err := client.SearchByISRC(ctx, "MISSING"); err == nil {
+		t.Fatal("expected missing ISRC error")
+	}
+
+	isrc, err := client.GetTrackISRC(ctx, "102")
+	if err != nil || isrc != "USRC17607840" {
+		t.Fatalf("GetTrackISRC = %q/%v", isrc, err)
+	}
+	albumID, err := client.GetTrackAlbumID(ctx, "101")
+	if err != nil || albumID != "201" {
+		t.Fatalf("GetTrackAlbumID = %q/%v", albumID, err)
+	}
+	extended, err := client.GetAlbumExtendedMetadata(ctx, "201")
+	if err != nil {
+		t.Fatalf("GetAlbumExtendedMetadata: %v", err)
+	}
+	if extended.Genre != "Pop, Dance" || extended.Label != "Label" {
+		t.Fatalf("extended = %#v", extended)
+	}
+	if byTrack, err := client.GetExtendedMetadataByTrackID(ctx, "101"); err != nil || byTrack.Label != "Label" {
+		t.Fatalf("metadata by track = %#v/%v", byTrack, err)
+	}
+	if byISRCMeta, err := client.GetExtendedMetadataByISRC(ctx, "USRC17607839"); err != nil || byISRCMeta.Label != "Label" {
+		t.Fatalf("metadata by isrc = %#v/%v", byISRCMeta, err)
+	}
+	if _, err := client.GetExtendedMetadataByISRC(ctx, ""); err == nil {
+		t.Fatal("expected empty ISRC metadata error")
+	}
+
+	if typ, id, err := parseDeezerURL("https://www.deezer.com/us/track/101"); err != nil || typ != "track" || id != "101" {
+		t.Fatalf("parseDeezerURL = %q/%q/%v", typ, id, err)
+	}
+	if _, _, err := parseDeezerURL("https://example.com/track/101"); err == nil {
+		t.Fatal("expected non-Deezer URL error")
+	}
+
+	client.cacheMu.Lock()
+	client.searchCache["expired"] = &cacheEntry{expiresAt: time.Now().Add(-time.Hour)}
+	client.searchCache["keep1"] = &cacheEntry{expiresAt: time.Now().Add(time.Hour)}
+	client.searchCache["keep2"] = &cacheEntry{expiresAt: time.Now().Add(2 * time.Hour)}
+	client.pruneExpiredCacheEntriesLocked(client.searchCache, time.Now())
+	client.trimCacheEntriesLocked(client.searchCache, 1)
+	client.isrcCache["1"] = "A"
+	client.isrcCache["2"] = "B"
+	client.trimStringCacheEntriesLocked(client.isrcCache, 1)
+	client.cacheMu.Unlock()
+}
@@ -25,7 +25,6 @@ var (
 )

 func GetISRCIndex(outputDir string) *ISRCIndex {
-	// Fast path: check cache first
 	isrcIndexCacheMu.RLock()
 	idx, exists := isrcIndexCache[outputDir]
 	isrcIndexCacheMu.RUnlock()
@@ -34,13 +33,11 @@ func GetISRCIndex(outputDir string) *ISRCIndex {
 		return idx
 	}

-	// Use per-directory mutex to prevent multiple goroutines from building simultaneously
 	buildLock, _ := isrcBuildingMu.LoadOrStore(outputDir, &sync.Mutex{})
 	mu := buildLock.(*sync.Mutex)
 	mu.Lock()
 	defer mu.Unlock()

-	// Double-check cache after acquiring lock (another goroutine may have built it)
 	isrcIndexCacheMu.RLock()
 	idx, exists = isrcIndexCache[outputDir]
 	isrcIndexCacheMu.RUnlock()
@@ -0,0 +1,83 @@
+package gobackend
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestExtensionPackageExportWrappers(t *testing.T) {
+	dir := t.TempDir()
+	extensionsDir := filepath.Join(dir, "extensions")
+	dataDir := filepath.Join(dir, "data")
+	if err := InitExtensionSystem(extensionsDir, dataDir); err != nil {
+		t.Fatalf("InitExtensionSystem: %v", err)
+	}
+	CleanupExtensions()
+	defer CleanupExtensions()
+
+	js := `
+registerExtension({
+  initialize: function(settings) { this.settings = settings || {}; },
+  cleanup: function() {},
+  doAction: function() { return { message: "wrapped", setting_updates: { quality: "lossless" } }; },
+  searchTracks: function() { return { tracks: [], total: 0 }; },
+  fetchLyrics: function() { return { syncType: "UNSYNCED", lines: [{ words: "hello" }] }; },
+  getDownloadUrl: function() { return { url: "https://example.test/a.flac" }; }
+});
+`
+	pkgV1 := filepath.Join(dir, "wrapper-ext-v1.spotiflac-ext")
+	pkgV2 := filepath.Join(dir, "wrapper-ext-v2.spotiflac-ext")
+	createTestExtensionPackage(t, pkgV1, "wrapper-ext", "1.0.0", js, nil)
+	createTestExtensionPackage(t, pkgV2, "wrapper-ext", "1.1.0", js, nil)
+
+	loadedJSON, err := LoadExtensionFromPath(pkgV1)
+	if err != nil || !strings.Contains(loadedJSON, "wrapper-ext") {
+		t.Fatalf("LoadExtensionFromPath = %q/%v", loadedJSON, err)
+	}
+	if installedJSON, err := GetInstalledExtensions(); err != nil || !strings.Contains(installedJSON, "wrapper-ext") {
+		t.Fatalf("GetInstalledExtensions = %q/%v", installedJSON, err)
+	}
+	if err := SetExtensionEnabledByID("wrapper-ext", true); err != nil {
+		t.Fatalf("SetExtensionEnabledByID true: %v", err)
+	}
+	if actionJSON, err := InvokeExtensionActionJSON("wrapper-ext", "doAction"); err != nil || !strings.Contains(actionJSON, "wrapped") {
+		t.Fatalf("InvokeExtensionActionJSON = %q/%v", actionJSON, err)
+	}
+	if upgradeJSON, err := CheckExtensionUpgradeFromPath(pkgV2); err != nil || !strings.Contains(upgradeJSON, `"can_upgrade":true`) {
+		t.Fatalf("CheckExtensionUpgradeFromPath = %q/%v", upgradeJSON, err)
+	}
+	if upgradedJSON, err := UpgradeExtensionFromPath(pkgV2); err != nil || !strings.Contains(upgradedJSON, "1.1.0") {
+		t.Fatalf("UpgradeExtensionFromPath = %q/%v", upgradedJSON, err)
+	}
+	if err := SetExtensionEnabledByID("wrapper-ext", false); err != nil {
+		t.Fatalf("SetExtensionEnabledByID false: %v", err)
+	}
+	if err := UnloadExtensionByID("wrapper-ext"); err != nil {
+		t.Fatalf("UnloadExtensionByID: %v", err)
+	}
+
+	dirExt := filepath.Join(extensionsDir, "wrapper-dir-ext")
+	if err := createDirectoryExtension(dirExt, "wrapper-dir-ext", "1.0.0"); err != nil {
+		t.Fatalf("create directory extension: %v", err)
+	}
+	if loadedDirJSON, err := LoadExtensionsFromDir(extensionsDir); err != nil || !strings.Contains(loadedDirJSON, "wrapper-dir-ext") {
+		t.Fatalf("LoadExtensionsFromDir = %q/%v", loadedDirJSON, err)
+	}
+	if err := RemoveExtensionByID("wrapper-dir-ext"); err != nil {
+		t.Fatalf("RemoveExtensionByID: %v", err)
+	}
+}
+
+func createDirectoryExtension(dir, name, version string) error {
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return err
+	}
+	manifest := fmt.Sprintf(`{"name":%q,"displayName":%q,"version":%q,"description":"Directory wrapper extension","type":["metadata_provider"],"permissions":{}}`, name, name, version)
+	if err := os.WriteFile(filepath.Join(dir, "manifest.json"), []byte(manifest), 0600); err != nil {
+		return err
+	}
+	return os.WriteFile(filepath.Join(dir, "index.js"), []byte(`registerExtension({searchTracks:function(){return {tracks:[], total:0};}});`), 0600)
+}
@@ -0,0 +1,158 @@
+package gobackend
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestLyricsExportWrappersWithoutNetwork(t *testing.T) {
+	dir := t.TempDir()
+	audioPath := filepath.Join(dir, "sidecar.mp3")
+	if err := os.WriteFile(audioPath, []byte("audio"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "sidecar.lrc"), []byte("[00:00.00]Sidecar lyric"), 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	if jsonText, err := FetchLyrics("spotify-1", "Song Instrumental", "Artist", 180000); err != nil || !strings.Contains(jsonText, `"instrumental":true`) {
+		t.Fatalf("FetchLyrics instrumental = %q/%v", jsonText, err)
+	}
+	if lrc, err := GetLyricsLRC("spotify-1", "Song Instrumental", "Artist", "", 180000); err != nil || lrc != "[instrumental:true]" {
+		t.Fatalf("GetLyricsLRC instrumental = %q/%v", lrc, err)
+	}
+	if jsonText, err := GetLyricsLRCWithSource("spotify-1", "Song Instrumental", "Artist", "", 180000); err != nil || !strings.Contains(jsonText, `"instrumental":true`) {
+		t.Fatalf("GetLyricsLRCWithSource instrumental = %q/%v", jsonText, err)
+	}
+	if lrc, err := GetLyricsLRC("", "", "", audioPath, 0); err != nil || !strings.Contains(lrc, "Sidecar lyric") {
+		t.Fatalf("GetLyricsLRC sidecar = %q/%v", lrc, err)
+	}
+	if jsonText, err := GetLyricsLRCWithSource("", "", "", audioPath, 0); err != nil || !strings.Contains(jsonText, "Sidecar lyric") {
+		t.Fatalf("GetLyricsLRCWithSource sidecar = %q/%v", jsonText, err)
+	}
+
+	outPath := filepath.Join(dir, "lyrics.lrc")
+	if err := FetchAndSaveLyrics("Song", "Artist", "", 0, outPath, audioPath); err != nil {
+		t.Fatalf("FetchAndSaveLyrics sidecar: %v", err)
+	}
+	if data := string(mustReadFile(t, outPath)); !strings.Contains(data, "Sidecar lyric") {
+		t.Fatalf("saved lyrics = %q", data)
+	}
+	if response, err := EmbedLyricsToFile(filepath.Join(dir, "not-flac.mp3"), "lyrics"); err != nil || !strings.Contains(response, `"success":false`) {
+		t.Fatalf("EmbedLyricsToFile error = %q/%v", response, err)
+	}
+	if response, err := RewriteSplitArtistTagsExport(filepath.Join(dir, "not-flac.mp3"), "A;B", "A"); err != nil || !strings.Contains(response, `"success":false`) {
+		t.Fatalf("RewriteSplitArtistTagsExport error = %q/%v", response, err)
+	}
+}
+
+func TestSongLinkExportWrappersWithFakeClient(t *testing.T) {
+	origClient := globalSongLinkClient
+	origRetryConfig := songLinkRetryConfig
+	origSearchByISRC := songLinkSearchByISRC
+	origCheckFromDeezer := songLinkCheckAvailabilityFromDeezer
+	defer func() {
+		globalSongLinkClient = origClient
+		songLinkRetryConfig = origRetryConfig
+		songLinkSearchByISRC = origSearchByISRC
+		songLinkCheckAvailabilityFromDeezer = origCheckFromDeezer
+		SetSongLinkNetworkOptions(false, false)
+	}()
+	songLinkRetryConfig = func() RetryConfig {
+		return RetryConfig{MaxRetries: 0, InitialDelay: 0, MaxDelay: 0, BackoffFactor: 1}
+	}
+	globalSongLinkClient = &SongLinkClient{client: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+		var body string
+		if req.URL.Host == "api.zarz.moe" {
+			body = `{"success":true,"songUrls":{"Spotify":"https://open.spotify.com/track/spotify-1","Deezer":"https://www.deezer.com/track/101","Tidal":"https://listen.tidal.com/track/202","YouTube":"https://youtu.be/yt1","AmazonMusic":"https://music.amazon.com/tracks/amz1","Qobuz":"https://open.qobuz.com/track/303"}}`
+		} else if req.URL.Host == "api.song.link" {
+			body = `{"linksByPlatform":{"spotify":{"url":"https://open.spotify.com/track/spotify-1"},"deezer":{"url":"https://www.deezer.com/track/101"},"tidal":{"url":"https://listen.tidal.com/track/202"},"youtubeMusic":{"url":"https://music.youtube.com/watch?v=ytm1"},"amazonMusic":{"url":"https://music.amazon.com/tracks/amz1"},"qobuz":{"url":"https://open.qobuz.com/track/303"}}}`
+		} else {
+			t.Fatalf("unexpected SongLink request: %s", req.URL.String())
+		}
+		return &http.Response{StatusCode: http.StatusOK, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(body)), Request: req}, nil
+	})}}
+	songLinkClientOnce.Do(func() {})
+
+	SetSongLinkNetworkOptions(true, true)
+	if availabilityJSON, err := CheckAvailability("spotify-1", ""); err != nil || !strings.Contains(availabilityJSON, `"deezer_id":"101"`) {
+		t.Fatalf("CheckAvailability = %q/%v", availabilityJSON, err)
+	}
+	if availabilityJSON, err := CheckAvailabilityFromDeezerID("101"); err != nil || !strings.Contains(availabilityJSON, `"spotify_id":"spotify-1"`) {
+		t.Fatalf("CheckAvailabilityFromDeezerID = %q/%v", availabilityJSON, err)
+	}
+	if availabilityJSON, err := CheckAvailabilityByPlatformID("deezer", "song", "101"); err != nil || !strings.Contains(availabilityJSON, `"tidal_url"`) {
+		t.Fatalf("CheckAvailabilityByPlatformID = %q/%v", availabilityJSON, err)
+	}
+	if spotifyID, err := GetSpotifyIDFromDeezerTrack("101"); err != nil || spotifyID != "spotify-1" {
+		t.Fatalf("GetSpotifyIDFromDeezerTrack = %q/%v", spotifyID, err)
+	}
+	if tidalURL, err := GetTidalURLFromDeezerTrack("101"); err != nil || !strings.Contains(tidalURL, "tidal") {
+		t.Fatalf("GetTidalURLFromDeezerTrack = %q/%v", tidalURL, err)
+	}
+	if urls, err := NewSongLinkClient().GetStreamingURLs("spotify-1"); err != nil || urls["tidal"] == "" || urls["amazon"] == "" {
+		t.Fatalf("GetStreamingURLs = %#v/%v", urls, err)
+	}
+	if youtubeURL, err := NewSongLinkClient().GetYouTubeURLFromSpotify("spotify-1"); err != nil || !strings.Contains(youtubeURL, "youtu") {
+		t.Fatalf("GetYouTubeURLFromSpotify = %q/%v", youtubeURL, err)
+	}
+	if amazonURL, err := NewSongLinkClient().GetAmazonURLFromDeezer("101"); err != nil || !strings.Contains(amazonURL, "amazon") {
+		t.Fatalf("GetAmazonURLFromDeezer = %q/%v", amazonURL, err)
+	}
+	if youtubeURL, err := NewSongLinkClient().GetYouTubeURLFromDeezer("101"); err != nil || !strings.Contains(youtubeURL, "youtube") {
+		t.Fatalf("GetYouTubeURLFromDeezer = %q/%v", youtubeURL, err)
+	}
+	if deezerID, err := NewSongLinkClient().GetDeezerIDFromSpotify("spotify-1"); err != nil || deezerID != "101" {
+		t.Fatalf("GetDeezerIDFromSpotify = %q/%v", deezerID, err)
+	}
+	if album, err := NewSongLinkClient().CheckAlbumAvailability("album-1"); err != nil || !album.Deezer || album.DeezerID == "" {
+		t.Fatalf("CheckAlbumAvailability = %#v/%v", album, err)
+	}
+	if albumID, err := NewSongLinkClient().GetDeezerAlbumIDFromSpotify("album-1"); err != nil || albumID == "" {
+		t.Fatalf("GetDeezerAlbumIDFromSpotify = %q/%v", albumID, err)
+	}
+	if availability, err := NewSongLinkClient().CheckAvailabilityFromURL("https://www.deezer.com/track/101"); err != nil || !availability.Deezer {
+		t.Fatalf("CheckAvailabilityFromURL = %#v/%v", availability, err)
+	}
+
+	songLinkSearchByISRC = func(ctx context.Context, isrc string) (*TrackMetadata, error) {
+		return &TrackMetadata{SpotifyID: "deezer:101", ExternalURL: "https://www.deezer.com/track/101"}, nil
+	}
+	songLinkCheckAvailabilityFromDeezer = func(s *SongLinkClient, deezerTrackID string) (*TrackAvailability, error) {
+		return &TrackAvailability{SpotifyID: "spotify-1", Deezer: true, DeezerID: deezerTrackID}, nil
+	}
+	if availabilityJSON, err := CheckAvailability("", "USRC17607839"); err != nil || !strings.Contains(availabilityJSON, `"deezer_id":"101"`) {
+		t.Fatalf("CheckAvailability by ISRC = %q/%v", availabilityJSON, err)
+	}
+	if songLinkExtractDeezerTrackID(nil) != "" || songLinkExtractDeezerTrackID(&TrackMetadata{ExternalURL: "https://www.deezer.com/track/202"}) != "202" {
+		t.Fatal("songLinkExtractDeezerTrackID mismatch")
+	}
+
+	deezerClient = &DeezerClient{
+		httpClient: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			body := fakeDeezerResponse(req.URL.Path, req.URL.RawQuery)
+			if body == "" {
+				body = `{"error":"missing"}`
+			}
+			return &http.Response{StatusCode: http.StatusOK, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(body)), Request: req}, nil
+		})},
+		searchCache:          map[string]*cacheEntry{},
+		albumCache:           map[string]*cacheEntry{},
+		artistCache:          map[string]*cacheEntry{},
+		isrcCache:            map[string]string{},
+		cacheCleanupInterval: time.Hour,
+	}
+	deezerClientOnce.Do(func() {})
+	if jsonText, err := ConvertSpotifyToDeezer("track", "spotify-1"); err != nil || !strings.Contains(jsonText, `"spotify_id":"deezer:101"`) {
+		t.Fatalf("ConvertSpotifyToDeezer track = %q/%v", jsonText, err)
+	}
+	if jsonText, err := ConvertSpotifyToDeezer("album", "album-1"); err != nil || jsonText == "" {
+		t.Fatalf("ConvertSpotifyToDeezer album = %q/%v", jsonText, err)
+	}
+}
@@ -0,0 +1,440 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestDownloadErrorClassificationPrioritizesRateLimit(t *testing.T) {
+	got := classifyDownloadErrorType("All providers failed. Last error: HTTP status 429: too many requests")
+	if got != "rate_limit" {
+		t.Fatalf("expected rate_limit, got %q", got)
+	}
+
+	responseJSON, err := errorResponse("All services failed. Last error: rate limit exceeded")
+	if err != nil {
+		t.Fatalf("errorResponse returned error: %v", err)
+	}
+
+	var response DownloadResponse
+	if err := json.Unmarshal([]byte(responseJSON), &response); err != nil {
+		t.Fatalf("invalid response JSON: %v", err)
+	}
+	if response.ErrorType != "rate_limit" {
+		t.Fatalf("expected rate_limit response, got %q", response.ErrorType)
+	}
+}
+
+func TestExportsJSONWrappersAndExtensionManagerSurface(t *testing.T) {
+	dir := t.TempDir()
+	dataDir := filepath.Join(dir, "data")
+	extensionsDir := filepath.Join(dir, "extensions")
+	if err := InitExtensionSystem(extensionsDir, dataDir); err != nil {
+		t.Fatalf("InitExtensionSystem: %v", err)
+	}
+
+	ext := newTestLoadedExtension(t, ExtensionTypeMetadataProvider, ExtensionTypeDownloadProvider, ExtensionTypeLyricsProvider)
+	manager := getExtensionManager()
+	manager.mu.Lock()
+	if manager.extensions == nil {
+		manager.extensions = map[string]*loadedExtension{}
+	}
+	manager.extensions[ext.ID] = ext
+	manager.mu.Unlock()
+	defer func() {
+		manager.mu.Lock()
+		delete(manager.extensions, ext.ID)
+		manager.mu.Unlock()
+	}()
+
+	if response, err := DownloadTrack(`{}`); err != nil || !strings.Contains(response, "retired") {
+		t.Fatalf("DownloadTrack = %q/%v", response, err)
+	}
+	if response, err := DownloadByStrategy(`not-json`); err != nil || !strings.Contains(response, "Invalid request") {
+		t.Fatalf("DownloadByStrategy invalid = %q/%v", response, err)
+	}
+	if response, err := DownloadByStrategy(`{"use_extensions":false}`); err != nil || !strings.Contains(response, "disabled") {
+		t.Fatalf("DownloadByStrategy disabled = %q/%v", response, err)
+	}
+	if response, err := DownloadWithFallback(`{}`); err != nil || !strings.Contains(response, "retired") {
+		t.Fatalf("DownloadWithFallback = %q/%v", response, err)
+	}
+
+	InitItemProgress("item-1")
+	FinishItemProgress("item-1")
+	ClearItemProgress("item-1")
+	CancelDownload("item-1")
+	if GetDownloadProgress() == "" || GetAllDownloadProgress() == "" || GetAllDownloadProgressDelta(0) == "" {
+		t.Fatal("expected progress JSON")
+	}
+	CleanupConnections()
+
+	cuePath, audioPath := writeExportCueFixture(t, dir)
+	if jsonText, err := ParseCueSheet(cuePath, ""); err != nil {
+		t.Fatalf("ParseCueSheet = %q/%v", jsonText, err)
+	} else {
+		var parsed CueSplitInfo
+		if err := json.Unmarshal([]byte(jsonText), &parsed); err != nil {
+			t.Fatalf("decode ParseCueSheet: %v", err)
+		}
+		if parsed.AudioPath != audioPath {
+			t.Fatalf("ParseCueSheet audio path = %q want %q", parsed.AudioPath, audioPath)
+		}
+	}
+	if jsonText, err := ScanCueSheetForLibrary(cuePath, "", "virtual.cue", 111); err != nil || !strings.Contains(jsonText, "cue+wav") {
+		t.Fatalf("ScanCueSheetForLibrary = %q/%v", jsonText, err)
+	}
+	if jsonText, err := ScanCueSheetForLibraryWithCoverCacheKey(cuePath, "", "virtual.cue", 111, "cover-key"); err != nil || !strings.Contains(jsonText, "cue+wav") {
+		t.Fatalf("ScanCueSheetForLibraryWithCoverCacheKey = %q/%v", jsonText, err)
+	}
+
+	apePath := filepath.Join(dir, "edit.ape")
+	if err := os.WriteFile(apePath, []byte("audio"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	editJSON := `{"title":"Edited","artist":"Artist","track_number":"1","track_total":"2","disc_number":"1","disc_total":"1"}`
+	if response, err := EditFileMetadata(apePath, editJSON); err != nil || !strings.Contains(response, "native_ape") {
+		t.Fatalf("EditFileMetadata ape = %q/%v", response, err)
+	}
+	if response, err := EditFileMetadata(filepath.Join(dir, "edit.mp3"), editJSON); err != nil || !strings.Contains(response, "ffmpeg") {
+		t.Fatalf("EditFileMetadata ffmpeg = %q/%v", response, err)
+	}
+	misnamedM4APath := filepath.Join(dir, "misnamed.flac")
+	if err := os.WriteFile(misnamedM4APath, buildM4AFileWithIlst(buildM4ATextTag("\xa9nam", "Misnamed"), true), 0600); err != nil {
+		t.Fatal(err)
+	}
+	replayGainJSON := `{"replaygain_track_gain":"-1 dB","replaygain_track_peak":"0.9"}`
+	if response, err := EditFileMetadata(misnamedM4APath, replayGainJSON); err != nil || !strings.Contains(response, "native_m4a_replaygain") {
+		t.Fatalf("EditFileMetadata misnamed m4a replaygain = %q/%v", response, err)
+	}
+	if _, err := EditFileMetadata(apePath, `not-json`); err == nil {
+		t.Fatal("expected invalid metadata JSON")
+	}
+	if !hasOnlyM4AReplayGainFields(map[string]string{"replaygain_track_gain": "-1 dB"}) {
+		t.Fatal("expected replaygain-only fields")
+	}
+	if hasOnlyM4AReplayGainFields(map[string]string{"title": "Song"}) {
+		t.Fatal("expected non-replaygain field rejection")
+	}
+
+	AllowDownloadDir(dir)
+	if err := SetDownloadDirectory(dir); err != nil {
+		t.Fatalf("SetDownloadDirectory: %v", err)
+	}
+	if duplicateJSON, err := CheckDuplicate(dir, ""); err != nil || !strings.Contains(duplicateJSON, "exists") {
+		t.Fatalf("CheckDuplicate = %q/%v", duplicateJSON, err)
+	}
+	if batchJSON, err := CheckDuplicatesBatch(dir, `[{"isrc":"","track_name":"Song","artist_name":"Artist"}]`); err != nil || !strings.Contains(batchJSON, "Song") {
+		t.Fatalf("CheckDuplicatesBatch = %q/%v", batchJSON, err)
+	}
+	_ = PreBuildDuplicateIndex(dir)
+	InvalidateDuplicateIndex(dir)
+	if filename, err := BuildFilename("{artist} - {title}", `{"artist":"A/B","title":"Song?"}`); err != nil || filename == "" {
+		t.Fatalf("BuildFilename = %q/%v", filename, err)
+	}
+	if _, err := BuildFilename("{title}", `not-json`); err == nil {
+		t.Fatal("expected BuildFilename JSON error")
+	}
+	if got := SanitizeFilename(`A/B:C*D?`); strings.ContainsAny(got, `/:*?`) {
+		t.Fatalf("SanitizeFilename = %q", got)
+	}
+
+	if response, err := PreWarmTrackCacheJSON(`not-json`); err != nil || !strings.Contains(response, "Invalid JSON") {
+		t.Fatalf("PreWarmTrackCacheJSON invalid = %q/%v", response, err)
+	}
+	if response, err := PreWarmTrackCacheJSON(`[{"isrc":"ISRC","track_name":"Song","artist_name":"Artist"}]`); err != nil || !strings.Contains(response, "success") {
+		t.Fatalf("PreWarmTrackCacheJSON = %q/%v", response, err)
+	}
+	if GetTrackCacheSize() != 0 {
+		t.Fatal("expected empty track cache")
+	}
+	ClearTrackIDCache()
+
+	if err := SetLyricsProvidersJSON(`["lrclib","apple_music"]`); err != nil {
+		t.Fatalf("SetLyricsProvidersJSON: %v", err)
+	}
+	if providers, err := GetLyricsProvidersJSON(); err != nil || !strings.Contains(providers, "lrclib") {
+		t.Fatalf("GetLyricsProvidersJSON = %q/%v", providers, err)
+	}
+	if available, err := GetAvailableLyricsProvidersJSON(); err != nil || available == "" {
+		t.Fatalf("GetAvailableLyricsProvidersJSON = %q/%v", available, err)
+	}
+	if err := SetLyricsFetchOptionsJSON(`{"include_translation_netease":true}`); err != nil {
+		t.Fatalf("SetLyricsFetchOptionsJSON: %v", err)
+	}
+	if opts, err := GetLyricsFetchOptionsJSON(); err != nil || opts == "" {
+		t.Fatalf("GetLyricsFetchOptionsJSON = %q/%v", opts, err)
+	}
+
+	if err := SetProviderPriorityJSON(`["coverage-ext"]`); err != nil {
+		t.Fatalf("SetProviderPriorityJSON: %v", err)
+	}
+	if jsonText, err := GetProviderPriorityJSON(); err != nil || !strings.Contains(jsonText, "coverage-ext") {
+		t.Fatalf("GetProviderPriorityJSON = %q/%v", jsonText, err)
+	}
+	if err := SetExtensionFallbackProviderIDsJSON(`["coverage-ext"]`); err != nil {
+		t.Fatalf("SetExtensionFallbackProviderIDsJSON: %v", err)
+	}
+	if jsonText, err := GetExtensionFallbackProviderIDsJSON(); err != nil || !strings.Contains(jsonText, "coverage-ext") {
+		t.Fatalf("GetExtensionFallbackProviderIDsJSON = %q/%v", jsonText, err)
+	}
+	if err := SetExtensionFallbackProviderIDsJSON(""); err != nil {
+		t.Fatalf("reset extension fallback IDs: %v", err)
+	}
+	if err := SetMetadataProviderPriorityJSON(`["coverage-ext"]`); err != nil {
+		t.Fatalf("SetMetadataProviderPriorityJSON: %v", err)
+	}
+	if jsonText, err := GetMetadataProviderPriorityJSON(); err != nil || !strings.Contains(jsonText, "coverage-ext") {
+		t.Fatalf("GetMetadataProviderPriorityJSON = %q/%v", jsonText, err)
+	}
+
+	if err := SetExtensionSettingsJSON(ext.ID, `{"quality":"lossless","_secret":"hidden"}`); err != nil {
+		t.Fatalf("SetExtensionSettingsJSON: %v", err)
+	}
+	if settingsJSON, err := GetExtensionSettingsJSON(ext.ID); err != nil || !strings.Contains(settingsJSON, "quality") {
+		t.Fatalf("GetExtensionSettingsJSON = %q/%v", settingsJSON, err)
+	}
+	if err := SetExtensionSettingsJSON(ext.ID, `not-json`); err == nil {
+		t.Fatal("expected settings JSON error")
+	}
+
+	if jsonText, err := SearchTracksWithExtensionsJSON("song", 5); err != nil || !strings.Contains(jsonText, "search-1") {
+		t.Fatalf("SearchTracksWithExtensionsJSON = %q/%v", jsonText, err)
+	}
+	if jsonText, err := SearchTracksWithMetadataProvidersJSON("song", 5, true); err != nil || !strings.Contains(jsonText, "search-1") {
+		t.Fatalf("SearchTracksWithMetadataProvidersJSON = %q/%v", jsonText, err)
+	}
+	if jsonText, err := GetProviderMetadataJSON(ext.ID, "track", "track-1"); err != nil || !strings.Contains(jsonText, "Track track-1") {
+		t.Fatalf("GetProviderMetadataJSON track = %q/%v", jsonText, err)
+	}
+	for _, resourceType := range []string{"album", "playlist", "artist"} {
+		if jsonText, err := GetProviderMetadataJSON(ext.ID, resourceType, resourceType+"-1"); err != nil || jsonText == "" {
+			t.Fatalf("GetProviderMetadataJSON %s = %q/%v", resourceType, jsonText, err)
+		}
+	}
+	if _, err := GetProviderMetadataJSON("", "track", "id"); err == nil {
+		t.Fatal("expected empty provider ID error")
+	}
+	if _, err := GetProviderMetadataJSON(ext.ID, "unsupported", "id"); err == nil {
+		t.Fatal("expected unsupported provider type")
+	}
+	if firstNonEmptyTrimmed(" ", " value ") != "value" {
+		t.Fatal("expected first trimmed value")
+	}
+	requestJSON := `{"use_extensions":true,"use_fallback":false,"service":"coverage-ext","source":"coverage-ext","track_name":"Song","artist_name":"Artist","album_name":"Album","output_dir":"` + escapeJSONPath(dir) + `","output_ext":".flac","quality":"LOSSLESS"}`
+	if jsonText, err := DownloadWithExtensionsJSON(requestJSON); err != nil || !strings.Contains(jsonText, "coverage-ext") {
+		t.Fatalf("DownloadWithExtensionsJSON = %q/%v", jsonText, err)
+	}
+	if _, err := DownloadWithExtensionsJSON(`not-json`); err == nil {
+		t.Fatal("expected DownloadWithExtensionsJSON JSON error")
+	}
+
+	SetExtensionAuthCodeByID(ext.ID, "code")
+	SetExtensionTokensByID(ext.ID, "access", "refresh", 60)
+	if !IsExtensionAuthenticatedByID(ext.ID) {
+		t.Fatal("expected authenticated extension")
+	}
+	if pending, err := GetExtensionPendingAuthJSON(ext.ID); err != nil || pending != "" {
+		t.Fatalf("GetExtensionPendingAuthJSON = %q/%v", pending, err)
+	}
+	ClearExtensionPendingAuthByID(ext.ID)
+	if all, err := GetAllPendingAuthRequestsJSON(); err != nil || all == "" {
+		t.Fatalf("GetAllPendingAuthRequestsJSON = %q/%v", all, err)
+	}
+
+	ffmpegCommandsMu.Lock()
+	ffmpegCommands["cmd-1"] = &FFmpegCommand{ExtensionID: ext.ID, Command: "ffmpeg -version", InputPath: "in", OutputPath: "out"}
+	ffmpegCommandsMu.Unlock()
+	if cmdJSON, err := GetPendingFFmpegCommandJSON("cmd-1"); err != nil || !strings.Contains(cmdJSON, "cmd-1") {
+		t.Fatalf("GetPendingFFmpegCommandJSON = %q/%v", cmdJSON, err)
+	}
+	if all, err := GetAllPendingFFmpegCommandsJSON(); err != nil || !strings.Contains(all, "cmd-1") {
+		t.Fatalf("GetAllPendingFFmpegCommandsJSON = %q/%v", all, err)
+	}
+	SetFFmpegCommandResultByID("cmd-1", true, "ok", "")
+	ClearFFmpegCommand("cmd-1")
+	if empty, err := GetPendingFFmpegCommandJSON("missing"); err != nil || empty != "" {
+		t.Fatalf("missing ffmpeg = %q/%v", empty, err)
+	}
+
+	enrichedJSON, err := EnrichTrackWithExtensionJSON(ext.ID, `{"id":"track-1","name":"Old","artists":"Artist"}`)
+	if err != nil || !strings.Contains(enrichedJSON, "Enriched") {
+		t.Fatalf("EnrichTrackWithExtensionJSON = %q/%v", enrichedJSON, err)
+	}
+	if sameJSON, err := EnrichTrackWithExtensionJSON("missing", `{"name":"Old"}`); err != nil || !strings.Contains(sameJSON, "Old") {
+		t.Fatalf("missing EnrichTrackWithExtensionJSON = %q/%v", sameJSON, err)
+	}
+
+	deezerClient = &DeezerClient{
+		httpClient: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			body := fakeDeezerResponse(req.URL.Path, req.URL.RawQuery)
+			status := http.StatusOK
+			if body == "" {
+				status = http.StatusNotFound
+				body = `{"error":"missing"}`
+			}
+			return &http.Response{StatusCode: status, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(body)), Request: req}, nil
+		})},
+		searchCache:          map[string]*cacheEntry{},
+		albumCache:           map[string]*cacheEntry{},
+		artistCache:          map[string]*cacheEntry{},
+		isrcCache:            map[string]string{},
+		cacheCleanupInterval: time.Hour,
+	}
+	deezerClientOnce.Do(func() {})
+	for _, item := range []struct {
+		typ string
+		id  string
+	}{
+		{"track", "101"},
+		{"album", "201"},
+		{"artist", "301"},
+		{"playlist", "401"},
+	} {
+		if jsonText, err := GetDeezerMetadata(item.typ, item.id); err != nil || jsonText == "" {
+			t.Fatalf("GetDeezerMetadata %s = %q/%v", item.typ, jsonText, err)
+		}
+	}
+	if _, err := GetDeezerMetadata("bad", "1"); err == nil {
+		t.Fatal("expected unsupported Deezer metadata type")
+	}
+	if jsonText, err := GetDeezerRelatedArtists("301", 2); err != nil || !strings.Contains(jsonText, "Related") {
+		t.Fatalf("GetDeezerRelatedArtists = %q/%v", jsonText, err)
+	}
+	if jsonText, err := GetDeezerExtendedMetadata("101"); err != nil || !strings.Contains(jsonText, "Label") {
+		t.Fatalf("GetDeezerExtendedMetadata = %q/%v", jsonText, err)
+	}
+	if _, err := GetDeezerExtendedMetadata(""); err == nil {
+		t.Fatal("expected empty Deezer metadata ID error")
+	}
+	if jsonText, err := SearchDeezerByISRC("USRC17607839"); err != nil || !strings.Contains(jsonText, "deezer:101") {
+		t.Fatalf("SearchDeezerByISRC = %q/%v", jsonText, err)
+	}
+	if jsonText, err := SearchDeezerByISRCForItemID("USRC17607839", "item-isrc"); err != nil || !strings.Contains(jsonText, "deezer:101") {
+		t.Fatalf("SearchDeezerByISRCForItemID = %q/%v", jsonText, err)
+	}
+
+	customJSON, err := CustomSearchWithExtensionJSON(ext.ID, "needle", `{"filter":"tracks"}`)
+	if err != nil || !strings.Contains(customJSON, "Custom needle") {
+		t.Fatalf("CustomSearchWithExtensionJSON = %q/%v", customJSON, err)
+	}
+	if customJSON, err := CustomSearchWithExtensionJSONWithRequestID(ext.ID, "needle", `not-json`, "req-custom"); err != nil || !strings.Contains(customJSON, "custom-1") {
+		t.Fatalf("CustomSearchWithExtensionJSONWithRequestID = %q/%v", customJSON, err)
+	}
+	if providersJSON, err := GetSearchProvidersJSON(); err != nil || !strings.Contains(providersJSON, "coverage-ext") {
+		t.Fatalf("GetSearchProvidersJSON = %q/%v", providersJSON, err)
+	}
+	if found := FindURLHandlerJSON("https://example.test/track/1"); found != ext.ID {
+		t.Fatalf("FindURLHandlerJSON = %q", found)
+	}
+	if handlersJSON, err := GetURLHandlersJSON(); err != nil || !strings.Contains(handlersJSON, "coverage-ext") {
+		t.Fatalf("GetURLHandlersJSON = %q/%v", handlersJSON, err)
+	}
+	if handledJSON, err := HandleURLWithExtensionJSON("https://example.test/track/1"); err != nil || !strings.Contains(handledJSON, "url-track") {
+		t.Fatalf("HandleURLWithExtensionJSON = %q/%v", handledJSON, err)
+	}
+	if postJSON, err := RunPostProcessingJSON(filepath.Join(dir, "song.flac"), `{"title":"Song"}`); err != nil || !strings.Contains(postJSON, "success") {
+		t.Fatalf("RunPostProcessingJSON = %q/%v", postJSON, err)
+	}
+	v2Input := `{"path":"` + escapeJSONPath(filepath.Join(dir, "song.flac")) + `","uri":"content://song","name":"song.flac","mime_type":"audio/flac","size":10}`
+	if postJSON, err := RunPostProcessingV2JSON(v2Input, `not-json`); err != nil || !strings.Contains(postJSON, "success") {
+		t.Fatalf("RunPostProcessingV2JSON = %q/%v", postJSON, err)
+	}
+	if postProviders, err := GetPostProcessingProvidersJSON(); err != nil || !strings.Contains(postProviders, "hook") {
+		t.Fatalf("GetPostProcessingProvidersJSON = %q/%v", postProviders, err)
+	}
+	if feedJSON, err := GetExtensionHomeFeedJSON(ext.ID); err != nil || !strings.Contains(feedJSON, "home-1") {
+		t.Fatalf("GetExtensionHomeFeedJSON = %q/%v", feedJSON, err)
+	}
+	if feedJSON, err := GetExtensionHomeFeedJSONWithRequestID(ext.ID, "req-home"); err != nil || !strings.Contains(feedJSON, "home-1") {
+		t.Fatalf("GetExtensionHomeFeedJSONWithRequestID = %q/%v", feedJSON, err)
+	}
+	if categoriesJSON, err := GetExtensionBrowseCategoriesJSON(ext.ID); err != nil || !strings.Contains(categoriesJSON, "cat-1") {
+		t.Fatalf("GetExtensionBrowseCategoriesJSON = %q/%v", categoriesJSON, err)
+	}
+	CancelExtensionRequestJSON("req-home")
+
+	storeDir := filepath.Join(dir, "store")
+	if err := InitExtensionStoreJSON(storeDir); err != nil {
+		t.Fatalf("InitExtensionStoreJSON: %v", err)
+	}
+	if err := SetStoreRegistryURLJSON("https://registry.example.com/index.json"); err != nil {
+		t.Fatalf("SetStoreRegistryURLJSON: %v", err)
+	}
+	store := getExtensionStore()
+	store.cache = &storeRegistry{Extensions: []storeExtension{{
+		ID:          "coverage-ext",
+		Name:        "coverage-ext",
+		Version:     "1.0.0",
+		Description: "Coverage",
+		Category:    CategoryMetadata,
+		Tags:        []string{"metadata"},
+		DownloadURL: "https://registry.example.com/coverage.spotiflac-ext",
+	}}}
+	store.cacheTime = time.Now()
+	if registryURL, err := GetStoreRegistryURLJSON(); err != nil || registryURL == "" {
+		t.Fatalf("GetStoreRegistryURLJSON = %q/%v", registryURL, err)
+	}
+	if storeJSON, err := GetStoreExtensionsJSON(false); err != nil || !strings.Contains(storeJSON, "coverage-ext") {
+		t.Fatalf("GetStoreExtensionsJSON = %q/%v", storeJSON, err)
+	}
+	if storeJSON, err := SearchStoreExtensionsJSON("coverage", CategoryMetadata); err != nil || !strings.Contains(storeJSON, "coverage-ext") {
+		t.Fatalf("SearchStoreExtensionsJSON = %q/%v", storeJSON, err)
+	}
+	if catsJSON, err := GetStoreCategoriesJSON(); err != nil || !strings.Contains(catsJSON, "metadata") {
+		t.Fatalf("GetStoreCategoriesJSON = %q/%v", catsJSON, err)
+	}
+	if dest, err := buildStoreExtensionDestPath(dir, "coverage/ext"); err != nil || !strings.HasSuffix(dest, ".spotiflac-ext") {
+		t.Fatalf("buildStoreExtensionDestPath = %q/%v", dest, err)
+	}
+	if _, err := buildStoreExtensionDestPath(dir, " "); err == nil {
+		t.Fatal("expected invalid extension id")
+	}
+	if err := ClearStoreCacheJSON(); err != nil {
+		t.Fatalf("ClearStoreCacheJSON: %v", err)
+	}
+	if err := ClearStoreRegistryURLJSON(); err != nil {
+		t.Fatalf("ClearStoreRegistryURLJSON: %v", err)
+	}
+
+	SetLibraryCoverCacheDirJSON(filepath.Join(dir, "covers"))
+	libraryDir := filepath.Join(dir, "library")
+	if err := os.MkdirAll(libraryDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(libraryDir, "Artist - Song.mp3"), []byte("not mp3"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if scanJSON, err := ScanLibraryFolderJSON(libraryDir); err != nil || !strings.Contains(scanJSON, "Song") {
+		t.Fatalf("ScanLibraryFolderJSON = %q/%v", scanJSON, err)
+	}
+	if scanJSON, err := ScanLibraryFolderIncrementalJSON(libraryDir, `[]`); err != nil || !strings.Contains(scanJSON, "Song") {
+		t.Fatalf("ScanLibraryFolderIncrementalJSON = %q/%v", scanJSON, err)
+	}
+	snapshotPath := filepath.Join(dir, "snapshot.json")
+	if err := os.WriteFile(snapshotPath, []byte(`[]`), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if scanJSON, err := ScanLibraryFolderIncrementalFromSnapshotJSON(libraryDir, snapshotPath); err != nil || !strings.Contains(scanJSON, "Song") {
+		t.Fatalf("ScanLibraryFolderIncrementalFromSnapshotJSON = %q/%v", scanJSON, err)
+	}
+	if GetLibraryScanProgressJSON() == "" {
+		t.Fatal("expected scan progress JSON")
+	}
+	CancelLibraryScanJSON()
+	if metadataJSON, err := ReadAudioMetadataJSON(filepath.Join(libraryDir, "missing.mp3")); err != nil || metadataJSON == "" {
+		t.Fatalf("ReadAudioMetadataJSON = %q/%v", metadataJSON, err)
+	}
+	if metadataJSON, err := ReadAudioMetadataWithHintJSON(filepath.Join(libraryDir, "missing.mp3"), "Missing"); err != nil || metadataJSON == "" {
+		t.Fatalf("ReadAudioMetadataWithHintJSON = %q/%v", metadataJSON, err)
+	}
+	if metadataJSON, err := ReadAudioMetadataWithHintAndCoverCacheKeyJSON(filepath.Join(libraryDir, "missing.mp3"), "Missing", "key"); err != nil || metadataJSON == "" {
+		t.Fatalf("ReadAudioMetadataWithHintAndCoverCacheKeyJSON = %q/%v", metadataJSON, err)
+	}
+}
@@ -1,6 +1,25 @@
 package gobackend

-import "testing"
+import (
+	"context"
+	"fmt"
+	"testing"
+)
+
+func TestSetExtensionFallbackProviderIDsJSONEmptyStringResetsDefault(t *testing.T) {
+	original := GetExtensionFallbackProviderIDs()
+	defer SetExtensionFallbackProviderIDs(original)
+
+	SetExtensionFallbackProviderIDs([]string{"custom-ext"})
+
+	if err := SetExtensionFallbackProviderIDsJSON(""); err != nil {
+		t.Fatalf("SetExtensionFallbackProviderIDsJSON returned error: %v", err)
+	}
+
+	if got := GetExtensionFallbackProviderIDs(); got != nil {
+		t.Fatalf("expected nil fallback provider list after reset, got %v", got)
+	}
+}

 func TestBuildDownloadSuccessResponsePrefersRequestedAlbumMetadata(t *testing.T) {
 	req := DownloadRequest{
@@ -113,3 +132,478 @@ func TestBuildDownloadSuccessResponsePrefersProviderCoverURL(t *testing.T) {
 		t.Fatalf("cover url = %q, want %q", resp.CoverURL, result.CoverURL)
 	}
 }
+
+func TestBuildDownloadSuccessResponseNormalizesDecryptionDescriptor(t *testing.T) {
+	req := DownloadRequest{
+		TrackName:  "Track",
+		ArtistName: "Artist",
+	}
+
+	result := DownloadResult{
+		Title:         "Track",
+		Artist:        "Artist",
+		DecryptionKey: "00112233",
+	}
+
+	resp := buildDownloadSuccessResponse(
+		req,
+		result,
+		"amazon",
+		"ok",
+		"/tmp/test.m4a",
+		false,
+	)
+
+	if resp.Decryption == nil {
+		t.Fatal("expected decryption descriptor to be present")
+	}
+	if resp.Decryption.Strategy != genericFFmpegMOVDecryptionStrategy {
+		t.Fatalf("strategy = %q", resp.Decryption.Strategy)
+	}
+	if resp.Decryption.Key != result.DecryptionKey {
+		t.Fatalf("key = %q, want %q", resp.Decryption.Key, result.DecryptionKey)
+	}
+}
+
+func TestFormatMusicBrainzGenrePrefersHighestCountTag(t *testing.T) {
+	got := formatMusicBrainzGenre([]musicBrainzTag{
+		{Name: "art pop", Count: 3},
+		{Name: "pop", Count: 8},
+		{Name: "dance pop", Count: 5},
+	})
+
+	if got != "Pop" {
+		t.Fatalf("genre = %q, want %q", got, "Pop")
+	}
+}
+
+func TestSelectMusicBrainzAlbumArtistPrefersMatchingRelease(t *testing.T) {
+	releases := []musicBrainzRelease{
+		{
+			Title: "Other Album",
+			ArtistCredit: []musicBrainzArtistCredit{
+				{Name: "Wrong Artist"},
+			},
+		},
+		{
+			Title: "Target Album",
+			ArtistCredit: []musicBrainzArtistCredit{
+				{Name: "Artist A", JoinPhrase: " & "},
+				{Name: "Artist B"},
+			},
+		},
+	}
+
+	got := selectMusicBrainzAlbumArtist(releases, "Target Album")
+	if got != "Artist A & Artist B" {
+		t.Fatalf("album artist = %q, want matching release artist credit", got)
+	}
+}
+
+func TestEnrichRequestExtendedMetadataUsesMusicBrainzAlbumArtist(t *testing.T) {
+	origDeezerFetcher := fetchDeezerExtendedMetadataByISRC
+	origMusicBrainzGenreFetcher := fetchMusicBrainzGenreByISRC
+	origMusicBrainzAlbumArtistFetcher := fetchMusicBrainzAlbumArtistByISRC
+	defer func() {
+		fetchDeezerExtendedMetadataByISRC = origDeezerFetcher
+		fetchMusicBrainzGenreByISRC = origMusicBrainzGenreFetcher
+		fetchMusicBrainzAlbumArtistByISRC = origMusicBrainzAlbumArtistFetcher
+	}()
+
+	fetchDeezerExtendedMetadataByISRC = func(ctx context.Context, isrc string) (*AlbumExtendedMetadata, error) {
+		return &AlbumExtendedMetadata{}, nil
+	}
+	fetchMusicBrainzGenreByISRC = func(isrc string) (string, error) {
+		return "", fmt.Errorf("no genre")
+	}
+	fetchMusicBrainzAlbumArtistByISRC = func(isrc string, albumName string) (string, error) {
+		if isrc != "TESTISRC" || albumName != "Target Album" {
+			t.Fatalf("unexpected MusicBrainz args: %q / %q", isrc, albumName)
+		}
+		return "MusicBrainz Album Artist", nil
+	}
+
+	req := DownloadRequest{
+		ISRC:       "TESTISRC",
+		ArtistName: "Track Artist",
+		AlbumName:  "Target Album",
+	}
+
+	enrichRequestExtendedMetadata(&req)
+
+	if req.AlbumArtist != "MusicBrainz Album Artist" {
+		t.Fatalf("album artist = %q, want MusicBrainz value", req.AlbumArtist)
+	}
+}
+
+func TestEnrichRequestExtendedMetadataDoesNotFallbackAlbumArtistToTrackArtist(t *testing.T) {
+	origDeezerFetcher := fetchDeezerExtendedMetadataByISRC
+	origMusicBrainzGenreFetcher := fetchMusicBrainzGenreByISRC
+	origMusicBrainzAlbumArtistFetcher := fetchMusicBrainzAlbumArtistByISRC
+	defer func() {
+		fetchDeezerExtendedMetadataByISRC = origDeezerFetcher
+		fetchMusicBrainzGenreByISRC = origMusicBrainzGenreFetcher
+		fetchMusicBrainzAlbumArtistByISRC = origMusicBrainzAlbumArtistFetcher
+	}()
+
+	fetchDeezerExtendedMetadataByISRC = func(ctx context.Context, isrc string) (*AlbumExtendedMetadata, error) {
+		return &AlbumExtendedMetadata{}, nil
+	}
+	fetchMusicBrainzGenreByISRC = func(isrc string) (string, error) {
+		return "", fmt.Errorf("no genre")
+	}
+	fetchMusicBrainzAlbumArtistByISRC = func(isrc string, albumName string) (string, error) {
+		return "", fmt.Errorf("no album artist")
+	}
+
+	req := DownloadRequest{
+		ISRC:       "TESTISRC",
+		ArtistName: "Track Artist",
+		AlbumName:  "Target Album",
+	}
+
+	enrichRequestExtendedMetadata(&req)
+
+	if req.AlbumArtist != "" {
+		t.Fatalf("album artist = %q, want empty when MusicBrainz has no value", req.AlbumArtist)
+	}
+}
+
+func TestEnrichExtraMetadataByISRCFallsBackToMusicBrainzGenre(t *testing.T) {
+	origDeezerFetcher := fetchDeezerExtendedMetadataByISRC
+	origMusicBrainzFetcher := fetchMusicBrainzGenreByISRC
+	defer func() {
+		fetchDeezerExtendedMetadataByISRC = origDeezerFetcher
+		fetchMusicBrainzGenreByISRC = origMusicBrainzFetcher
+	}()
+
+	fetchDeezerExtendedMetadataByISRC = func(ctx context.Context, isrc string) (*AlbumExtendedMetadata, error) {
+		return nil, nil
+	}
+	fetchMusicBrainzGenreByISRC = func(isrc string) (string, error) {
+		if isrc != "TEST123" {
+			t.Fatalf("unexpected isrc: %q", isrc)
+		}
+		return "Alternative Rock", nil
+	}
+
+	genre := ""
+	label := ""
+	copyright := ""
+	enrichExtraMetadataByISRC("DownloadWithFallback", "TEST123", &genre, &label, &copyright)
+
+	if genre != "Alternative Rock" {
+		t.Fatalf("genre = %q, want fallback genre", genre)
+	}
+	if label != "" {
+		t.Fatalf("label = %q, want empty", label)
+	}
+	if copyright != "" {
+		t.Fatalf("copyright = %q, want empty", copyright)
+	}
+}
+
+func TestEnrichExtraMetadataByISRCPrefersDeezerGenre(t *testing.T) {
+	origDeezerFetcher := fetchDeezerExtendedMetadataByISRC
+	origMusicBrainzFetcher := fetchMusicBrainzGenreByISRC
+	defer func() {
+		fetchDeezerExtendedMetadataByISRC = origDeezerFetcher
+		fetchMusicBrainzGenreByISRC = origMusicBrainzFetcher
+	}()
+
+	musicBrainzCalled := false
+	fetchDeezerExtendedMetadataByISRC = func(ctx context.Context, isrc string) (*AlbumExtendedMetadata, error) {
+		return &AlbumExtendedMetadata{
+			Genre:     "Synthpop",
+			Label:     "EMI",
+			Copyright: "(C) Test",
+		}, nil
+	}
+	fetchMusicBrainzGenreByISRC = func(isrc string) (string, error) {
+		musicBrainzCalled = true
+		return "Rock", nil
+	}
+
+	genre := ""
+	label := ""
+	copyright := ""
+	enrichExtraMetadataByISRC("DownloadWithFallback", "TEST456", &genre, &label, &copyright)
+
+	if genre != "Synthpop" {
+		t.Fatalf("genre = %q, want Deezer genre", genre)
+	}
+	if label != "EMI" {
+		t.Fatalf("label = %q, want Deezer label", label)
+	}
+	if copyright != "(C) Test" {
+		t.Fatalf("copyright = %q, want Deezer copyright", copyright)
+	}
+	if musicBrainzCalled {
+		t.Fatal("expected MusicBrainz not to be called when Deezer already provides genre")
+	}
+}
+
+func TestApplyReEnrichTrackMetadataPreservesExistingReleaseDateWhenCandidateMissing(t *testing.T) {
+	req := reEnrichRequest{
+		SpotifyID:   "spotify-track-id",
+		AlbumName:   "Original Album",
+		ReleaseDate: "2024-01-01",
+		ISRC:        "REQ123",
+	}
+
+	applyReEnrichTrackMetadata(&req, ExtTrackMetadata{
+		AlbumName:   "Resolved Album",
+		ReleaseDate: "",
+		ISRC:        "",
+	})
+
+	if req.ReleaseDate != "2024-01-01" {
+		t.Fatalf("release date = %q, want existing value preserved", req.ReleaseDate)
+	}
+	if req.AlbumName != "Resolved Album" {
+		t.Fatalf("album = %q, want updated album", req.AlbumName)
+	}
+	if req.ISRC != "REQ123" {
+		t.Fatalf("isrc = %q, want existing value preserved", req.ISRC)
+	}
+}
+
+func TestSelectBestReEnrichTrackPrefersCandidateWithReleaseDate(t *testing.T) {
+	req := reEnrichRequest{
+		TrackName:   "Song Title",
+		ArtistName:  "Artist Name",
+		AlbumName:   "Album Name",
+		ReleaseDate: "",
+		DurationMs:  180000,
+	}
+
+	tracks := []ExtTrackMetadata{
+		{
+			ID:          "first",
+			Name:        "Song Title",
+			Artists:     "Artist Name",
+			AlbumName:   "Album Name",
+			DurationMS:  180000,
+			ReleaseDate: "",
+			ProviderID:  "spotify",
+		},
+		{
+			ID:          "second",
+			Name:        "Song Title",
+			Artists:     "Artist Name",
+			AlbumName:   "Album Name",
+			DurationMS:  180000,
+			ReleaseDate: "2024-03-09",
+			ProviderID:  "deezer",
+		},
+	}
+
+	best := selectBestReEnrichTrack(req, tracks)
+	if best == nil {
+		t.Fatal("expected a selected track")
+	}
+	if best.ID != "second" {
+		t.Fatalf("selected track = %q, want candidate with release date", best.ID)
+	}
+}
+
+func TestSelectBestReEnrichTrackRejectsMismatchedSearchResults(t *testing.T) {
+	req := reEnrichRequest{
+		TrackName:  "Song Title",
+		ArtistName: "Artist Name",
+		AlbumName:  "Album Name",
+		DurationMs: 180000,
+	}
+
+	tracks := []ExtTrackMetadata{
+		{
+			ID:          "wrong-rich-metadata",
+			Name:        "Different Song",
+			Artists:     "Different Artist",
+			AlbumName:   "Album Name",
+			DurationMS:  180000,
+			ReleaseDate: "2024-03-09",
+			TrackNumber: 4,
+			DiscNumber:  1,
+			ISRC:        "WRONG1234567",
+			ProviderID:  "deezer",
+		},
+	}
+
+	if best := selectBestReEnrichTrack(req, tracks); best != nil {
+		t.Fatalf("selected track = %q, want no match", best.ID)
+	}
+}
+
+func TestSelectBestReEnrichTrackAllowsExactISRCDespiteMetadataMismatch(t *testing.T) {
+	req := reEnrichRequest{
+		TrackName:  "Song Title",
+		ArtistName: "Artist Name",
+		ISRC:       "USRC17607839",
+		DurationMs: 999999000,
+	}
+
+	tracks := []ExtTrackMetadata{
+		{
+			ID:         "same-isrc",
+			Name:       "Different Song",
+			Artists:    "Different Artist",
+			DurationMS: 180000,
+			ISRC:       "USRC17607839",
+			ProviderID: "deezer",
+		},
+	}
+
+	best := selectBestReEnrichTrack(req, tracks)
+	if best == nil {
+		t.Fatal("expected exact ISRC candidate to be selected")
+	}
+	if best.ID != "same-isrc" {
+		t.Fatalf("selected track = %q, want exact ISRC candidate", best.ID)
+	}
+}
+
+func TestSelectBestReEnrichTrackPlaceholderFallsBackToAlbum(t *testing.T) {
+	req := reEnrichRequest{
+		TrackName:  "Unknown Title",
+		ArtistName: "Unknown Artist",
+		AlbumName:  "Harry Styles",
+		DurationMs: 180000,
+	}
+
+	tracks := []ExtTrackMetadata{
+		{
+			ID:         "album-match",
+			Name:       "Sign of the Times",
+			Artists:    "Harry Styles",
+			AlbumName:  "Harry Styles",
+			DurationMS: 180000,
+			ProviderID: "deezer",
+		},
+	}
+
+	best := selectBestReEnrichTrack(req, tracks)
+	if best == nil {
+		t.Fatal("expected album-matching candidate to be selected when title/artist are placeholders")
+	}
+	if best.ID != "album-match" {
+		t.Fatalf("selected track = %q, want album-match", best.ID)
+	}
+}
+
+func TestBuildReEnrichFFmpegMetadataOmitsEmptyFields(t *testing.T) {
+	req := reEnrichRequest{
+		TrackName:   "Song",
+		ArtistName:  "Artist",
+		AlbumName:   "Album",
+		AlbumArtist: "",
+		ReleaseDate: "",
+		TrackNumber: 0,
+		DiscNumber:  0,
+		ISRC:        "",
+		Genre:       "",
+		Label:       "",
+		Copyright:   "",
+	}
+
+	metadata := buildReEnrichFFmpegMetadata(&req, "")
+
+	if metadata["TITLE"] != "Song" {
+		t.Fatalf("title = %q", metadata["TITLE"])
+	}
+	if metadata["ARTIST"] != "Artist" {
+		t.Fatalf("artist = %q", metadata["ARTIST"])
+	}
+	if metadata["ALBUM"] != "Album" {
+		t.Fatalf("album = %q", metadata["ALBUM"])
+	}
+
+	for _, key := range []string{
+		"ALBUMARTIST",
+		"DATE",
+		"TRACKNUMBER",
+		"DISCNUMBER",
+		"ISRC",
+		"GENRE",
+		"ORGANIZATION",
+		"COPYRIGHT",
+		"LYRICS",
+		"UNSYNCEDLYRICS",
+	} {
+		if _, exists := metadata[key]; exists {
+			t.Fatalf("did not expect key %s in metadata: %#v", key, metadata)
+		}
+	}
+}
+
+func TestBuildReEnrichSearchQuerySkipsPlaceholderArtist(t *testing.T) {
+	req := reEnrichRequest{
+		TrackName:  "Sign of the Times",
+		ArtistName: "Unknown Artist",
+		AlbumName:  "Harry Styles",
+	}
+
+	query := buildReEnrichSearchQuery(req)
+	if query != "Sign of the Times" {
+		t.Fatalf("query = %q", query)
+	}
+
+	req = reEnrichRequest{
+		TrackName:  "Unknown Title",
+		ArtistName: "Unknown Artist",
+		AlbumName:  "Harry Styles",
+	}
+	query = buildReEnrichSearchQuery(req)
+	if query != "Harry Styles" {
+		t.Fatalf("fallback album query = %q", query)
+	}
+}
+
+func TestApplyReEnrichTrackMetadataCopiesComposerAndTotals(t *testing.T) {
+	req := reEnrichRequest{}
+
+	applyReEnrichTrackMetadata(&req, ExtTrackMetadata{
+		Name:        "Resolved Song",
+		Artists:     "Resolved Artist",
+		TrackNumber: 7,
+		TotalTracks: 12,
+		DiscNumber:  2,
+		TotalDiscs:  3,
+		Composer:    "Composer",
+	})
+
+	if req.TrackNumber != 7 || req.TotalTracks != 12 {
+		t.Fatalf("track metadata = %d/%d", req.TrackNumber, req.TotalTracks)
+	}
+	if req.DiscNumber != 2 || req.TotalDiscs != 3 {
+		t.Fatalf("disc metadata = %d/%d", req.DiscNumber, req.TotalDiscs)
+	}
+	if req.TrackName != "Resolved Song" || req.ArtistName != "Resolved Artist" {
+		t.Fatalf("basic tags = %q / %q", req.TrackName, req.ArtistName)
+	}
+	if req.Composer != "Composer" {
+		t.Fatalf("composer = %q", req.Composer)
+	}
+}
+
+func TestBuildReEnrichFFmpegMetadataFormatsTotalsAndComposer(t *testing.T) {
+	req := reEnrichRequest{
+		TrackNumber: 7,
+		TotalTracks: 12,
+		DiscNumber:  2,
+		TotalDiscs:  3,
+		Composer:    "Composer",
+	}
+
+	metadata := buildReEnrichFFmpegMetadata(&req, "")
+
+	if metadata["TRACKNUMBER"] != "7/12" {
+		t.Fatalf("TRACKNUMBER = %q", metadata["TRACKNUMBER"])
+	}
+	if metadata["DISCNUMBER"] != "2/3" {
+		t.Fatalf("DISCNUMBER = %q", metadata["DISCNUMBER"])
+	}
+	if metadata["COMPOSER"] != "Composer" {
+		t.Fatalf("COMPOSER = %q", metadata["COMPOSER"])
+	}
+}
@@ -0,0 +1,390 @@
+package gobackend
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	extensionHealthDefaultTimeout = 4 * time.Second
+	extensionHealthMaxBodyBytes   = 64 * 1024
+	extensionHealthDefaultCache   = 60 * time.Second
+)
+
+type ExtensionHealthResult struct {
+	ExtensionID string                       `json:"extension_id"`
+	Status      string                       `json:"status"`
+	CheckedAt   string                       `json:"checked_at"`
+	Checks      []ExtensionHealthCheckResult `json:"checks"`
+}
+
+type ExtensionHealthCheckResult struct {
+	ID         string `json:"id"`
+	Label      string `json:"label,omitempty"`
+	URL        string `json:"url"`
+	Method     string `json:"method"`
+	ServiceKey string `json:"service_key,omitempty"`
+	Required   bool   `json:"required"`
+	Status     string `json:"status"`
+	HTTPStatus int    `json:"http_status,omitempty"`
+	LatencyMs  int64  `json:"latency_ms"`
+	Message    string `json:"message,omitempty"`
+	Error      string `json:"error,omitempty"`
+	CheckedAt  string `json:"checked_at"`
+}
+
+type cachedExtensionHealthResult struct {
+	result    ExtensionHealthResult
+	expiresAt time.Time
+}
+
+var (
+	extensionHealthCacheMu sync.Mutex
+	extensionHealthCache   = map[string]cachedExtensionHealthResult{}
+)
+
+func CheckExtensionHealthJSON(extensionID string) (string, error) {
+	manager := getExtensionManager()
+	ext, err := manager.GetExtension(extensionID)
+	if err != nil {
+		return "", err
+	}
+
+	result := CheckExtensionHealth(ext)
+	bytes, err := json.Marshal(result)
+	if err != nil {
+		return "", err
+	}
+	return string(bytes), nil
+}
+
+func CheckExtensionHealthCached(ext *loadedExtension) ExtensionHealthResult {
+	if ext == nil || ext.Manifest == nil || len(ext.Manifest.ServiceHealth) == 0 {
+		return CheckExtensionHealth(ext)
+	}
+
+	cacheKey := strings.TrimSpace(ext.ID)
+	if cacheKey == "" {
+		return CheckExtensionHealth(ext)
+	}
+
+	now := time.Now()
+	extensionHealthCacheMu.Lock()
+	cached, ok := extensionHealthCache[cacheKey]
+	if ok && now.Before(cached.expiresAt) {
+		extensionHealthCacheMu.Unlock()
+		return cached.result
+	}
+	extensionHealthCacheMu.Unlock()
+
+	result := CheckExtensionHealth(ext)
+	ttl := extensionHealthCacheTTL(ext.Manifest.ServiceHealth)
+
+	extensionHealthCacheMu.Lock()
+	extensionHealthCache[cacheKey] = cachedExtensionHealthResult{
+		result:    result,
+		expiresAt: now.Add(ttl),
+	}
+	extensionHealthCacheMu.Unlock()
+
+	return result
+}
+
+func CheckExtensionHealth(ext *loadedExtension) ExtensionHealthResult {
+	now := time.Now().UTC().Format(time.RFC3339)
+	result := ExtensionHealthResult{
+		ExtensionID: "",
+		Status:      "unsupported",
+		CheckedAt:   now,
+		Checks:      []ExtensionHealthCheckResult{},
+	}
+	if ext == nil || ext.Manifest == nil {
+		result.Status = "offline"
+		return result
+	}
+
+	result.ExtensionID = ext.ID
+	checks := ext.Manifest.ServiceHealth
+	if len(checks) == 0 {
+		return result
+	}
+
+	result.Status = "online"
+	for _, check := range checks {
+		checkResult := runExtensionHealthCheck(ext.Manifest, check)
+		result.Checks = append(result.Checks, checkResult)
+
+		switch checkResult.Status {
+		case "offline":
+			if check.Required {
+				result.Status = "offline"
+			} else if result.Status == "online" {
+				result.Status = "degraded"
+			}
+		case "degraded":
+			if result.Status == "online" {
+				result.Status = "degraded"
+			}
+		case "unknown":
+			if result.Status == "online" {
+				result.Status = "unknown"
+			}
+		}
+	}
+
+	return result
+}
+
+func extensionHealthCacheTTL(checks []ExtensionHealthCheck) time.Duration {
+	ttl := extensionHealthDefaultCache
+	for _, check := range checks {
+		if check.CacheTTLSeconds <= 0 {
+			continue
+		}
+		checkTTL := time.Duration(check.CacheTTLSeconds) * time.Second
+		if checkTTL < ttl {
+			ttl = checkTTL
+		}
+	}
+	return ttl
+}
+
+func runExtensionHealthCheck(manifest *ExtensionManifest, check ExtensionHealthCheck) ExtensionHealthCheckResult {
+	method := strings.ToUpper(strings.TrimSpace(check.Method))
+	if method == "" {
+		method = http.MethodGet
+	}
+	now := time.Now().UTC().Format(time.RFC3339)
+	result := ExtensionHealthCheckResult{
+		ID:         check.ID,
+		Label:      check.Label,
+		URL:        check.URL,
+		Method:     method,
+		ServiceKey: strings.TrimSpace(check.ServiceKey),
+		Required:   check.Required,
+		Status:     "unknown",
+		CheckedAt:  now,
+	}
+
+	parsed, err := url.Parse(check.URL)
+	if err != nil {
+		result.Status = "offline"
+		result.Error = fmt.Sprintf("invalid health URL: %v", err)
+		return result
+	}
+	if parsed.Scheme != "https" {
+		result.Status = "offline"
+		result.Error = "health check must use https"
+		return result
+	}
+	host := parsed.Hostname()
+	if host == "" {
+		result.Status = "offline"
+		result.Error = "health check URL hostname is required"
+		return result
+	}
+	if isPrivateIP(host) {
+		result.Status = "offline"
+		result.Error = "private/local health check host is not allowed"
+		return result
+	}
+	if manifest == nil || !manifest.IsDomainAllowed(host) {
+		result.Status = "offline"
+		result.Error = fmt.Sprintf("health check host '%s' is not in extension network permissions", host)
+		return result
+	}
+	if method != http.MethodGet && method != http.MethodHead {
+		result.Status = "offline"
+		result.Error = "health check method must be GET or HEAD"
+		return result
+	}
+
+	timeout := extensionHealthDefaultTimeout
+	if check.TimeoutMs > 0 {
+		timeout = time.Duration(check.TimeoutMs) * time.Millisecond
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, method, check.URL, nil)
+	if err != nil {
+		result.Status = "offline"
+		result.Error = err.Error()
+		return result
+	}
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("User-Agent", userAgentForURL(parsed))
+
+	start := time.Now()
+	resp, err := NewMetadataHTTPClient(timeout).Do(req)
+	result.LatencyMs = time.Since(start).Milliseconds()
+	if err != nil {
+		result.Status = "offline"
+		result.Error = err.Error()
+		return result
+	}
+	defer resp.Body.Close()
+
+	result.HTTPStatus = resp.StatusCode
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		result.Status = "offline"
+		result.Message = resp.Status
+		return result
+	}
+
+	if method == http.MethodHead {
+		result.Status = "online"
+		result.Message = resp.Status
+		return result
+	}
+
+	body, err := io.ReadAll(io.LimitReader(resp.Body, extensionHealthMaxBodyBytes))
+	if err != nil {
+		result.Status = "degraded"
+		result.Error = err.Error()
+		return result
+	}
+
+	status, message := classifyExtensionHealthBody(body, check.ServiceKey)
+	result.Status = status
+	if message == "" {
+		result.Message = resp.Status
+	} else {
+		result.Message = message
+	}
+	return result
+}
+
+func classifyExtensionHealthBody(body []byte, serviceKey string) (string, string) {
+	if len(strings.TrimSpace(string(body))) == 0 {
+		return "online", ""
+	}
+
+	var payload map[string]interface{}
+	if err := json.Unmarshal(body, &payload); err != nil {
+		return "online", ""
+	}
+
+	serviceKey = strings.TrimSpace(serviceKey)
+	if serviceKey != "" {
+		if status, message, ok := classifyExtensionHealthService(payload, serviceKey); ok {
+			return status, message
+		}
+	}
+
+	rawStatus, _ := payload["status"].(string)
+	normalized := strings.ToLower(strings.TrimSpace(rawStatus))
+	switch normalized {
+	case "", "ok", "up", "online", "healthy", "operational", "pass", "passing":
+		return "online", rawStatus
+	case "degraded", "partial", "warning", "warn":
+		return "degraded", rawStatus
+	case "down", "offline", "error", "failed", "fail", "unhealthy":
+		return "offline", rawStatus
+	default:
+		return "online", rawStatus
+	}
+}
+
+func classifyExtensionHealthService(payload map[string]interface{}, serviceKey string) (string, string, bool) {
+	rawServices, ok := payload["services"]
+	if !ok {
+		return "", "", false
+	}
+	services, ok := rawServices.(map[string]interface{})
+	if !ok {
+		return "", "", false
+	}
+	rawService, ok := services[serviceKey]
+	if !ok {
+		return "unknown", fmt.Sprintf("service '%s' not found", serviceKey), true
+	}
+	service, ok := rawService.(map[string]interface{})
+	if !ok {
+		return "unknown", fmt.Sprintf("service '%s' has invalid health payload", serviceKey), true
+	}
+
+	label, _ := service["label"].(string)
+	detail, _ := service["detail"].(string)
+	errText, _ := service["error"].(string)
+	messageParts := []string{}
+	if strings.TrimSpace(label) != "" {
+		messageParts = append(messageParts, strings.TrimSpace(label))
+	}
+	if strings.TrimSpace(detail) != "" {
+		messageParts = append(messageParts, strings.TrimSpace(detail))
+	}
+	if strings.TrimSpace(errText) != "" {
+		messageParts = append(messageParts, strings.TrimSpace(errText))
+	}
+
+	rawStatus, hasStatus := service["status"]
+	okValue, hasOK := service["ok"].(bool)
+	if statusCode, ok := healthNumber(rawStatus); ok {
+		if statusCode >= 200 && statusCode < 300 {
+			return "online", strings.Join(messageParts, ": "), true
+		}
+		if statusCode == http.StatusUnauthorized || statusCode == http.StatusForbidden {
+			return "degraded", strings.Join(messageParts, ": "), true
+		}
+		if statusCode == http.StatusInternalServerError && hasOK && okValue {
+			return "online", strings.Join(messageParts, ": "), true
+		}
+		return "offline", strings.Join(messageParts, ": "), true
+	}
+
+	if isExtensionHealthAuthRequired(detail) {
+		return "degraded", strings.Join(messageParts, ": "), true
+	}
+	if hasOK {
+		if okValue {
+			return "online", strings.Join(messageParts, ": "), true
+		}
+		return "offline", strings.Join(messageParts, ": "), true
+	}
+	if !hasStatus {
+		return "unknown", strings.Join(messageParts, ": "), true
+	}
+
+	statusString := strings.ToLower(strings.TrimSpace(fmt.Sprintf("%v", rawStatus)))
+	switch statusString {
+	case "ok", "up", "online", "healthy", "operational":
+		return "online", strings.Join(messageParts, ": "), true
+	case "degraded", "partial", "warning", "warn":
+		return "degraded", strings.Join(messageParts, ": "), true
+	case "down", "offline", "error", "failed", "fail", "unhealthy":
+		return "offline", strings.Join(messageParts, ": "), true
+	default:
+		return "unknown", strings.Join(messageParts, ": "), true
+	}
+}
+
+func isExtensionHealthAuthRequired(detail string) bool {
+	switch strings.ToLower(strings.TrimSpace(detail)) {
+	case "auth_required", "authorization_required", "login_required", "unauthorized":
+		return true
+	default:
+		return false
+	}
+}
+
+func healthNumber(value interface{}) (int, bool) {
+	switch v := value.(type) {
+	case float64:
+		return int(v), true
+	case int:
+		return v, true
+	case json.Number:
+		n, err := v.Int64()
+		return int(n), err == nil
+	default:
+		return 0, false
+	}
+}
@@ -0,0 +1,143 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+)
+
+func TestExtensionHealthClassificationAndValidation(t *testing.T) {
+	if status, msg := classifyExtensionHealthBody([]byte(`{"status":"degraded"}`), ""); status != "degraded" || msg != "degraded" {
+		t.Fatalf("status/message = %q/%q", status, msg)
+	}
+	if status, _ := classifyExtensionHealthBody([]byte(`not-json`), ""); status != "online" {
+		t.Fatalf("invalid JSON status = %q", status)
+	}
+	if status, msg := classifyExtensionHealthBody([]byte(`{"services":{"tidal":{"status":401,"label":"Tidal","detail":"auth_required"}}}`), "tidal"); status != "degraded" || !strings.Contains(msg, "Tidal") {
+		t.Fatalf("service status/message = %q/%q", status, msg)
+	}
+	if status, msg, ok := classifyExtensionHealthService(map[string]interface{}{"services": map[string]interface{}{}}, "missing"); !ok || status != "unknown" || !strings.Contains(msg, "missing") {
+		t.Fatalf("missing service = %q/%q/%v", status, msg, ok)
+	}
+	if n, ok := healthNumber(json.Number("503")); !ok || n != 503 {
+		t.Fatalf("health number = %d/%v", n, ok)
+	}
+	if !isExtensionHealthAuthRequired(" unauthorized ") {
+		t.Fatal("expected auth required")
+	}
+
+	if result := CheckExtensionHealth(nil); result.Status != "offline" {
+		t.Fatalf("nil health = %#v", result)
+	}
+	manifest := &ExtensionManifest{Permissions: ExtensionPermissions{Network: []string{"status.example.com"}}}
+	invalidURL := runExtensionHealthCheck(manifest, ExtensionHealthCheck{ID: "bad", URL: "://bad"})
+	if invalidURL.Status != "offline" {
+		t.Fatalf("invalid URL = %#v", invalidURL)
+	}
+	insecure := runExtensionHealthCheck(manifest, ExtensionHealthCheck{ID: "http", URL: "http://status.example.com"})
+	if insecure.Status != "offline" || !strings.Contains(insecure.Error, "https") {
+		t.Fatalf("insecure = %#v", insecure)
+	}
+	disallowedHost := runExtensionHealthCheck(manifest, ExtensionHealthCheck{ID: "host", URL: "https://other.example.com"})
+	if disallowedHost.Status != "offline" || !strings.Contains(disallowedHost.Error, "permissions") {
+		t.Fatalf("host = %#v", disallowedHost)
+	}
+	badMethod := runExtensionHealthCheck(manifest, ExtensionHealthCheck{ID: "method", URL: "https://status.example.com", Method: "POST"})
+	if badMethod.Status != "offline" || !strings.Contains(badMethod.Error, "method") {
+		t.Fatalf("method = %#v", badMethod)
+	}
+
+	ext := &loadedExtension{
+		ID: "health-ext",
+		Manifest: &ExtensionManifest{
+			ServiceHealth: []ExtensionHealthCheck{
+				{ID: "required", URL: "http://status.example.com", Required: true},
+				{ID: "optional", URL: "http://status.example.com", Required: false},
+			},
+		},
+	}
+	if result := CheckExtensionHealth(ext); result.Status != "offline" || len(result.Checks) != 2 {
+		t.Fatalf("extension health = %#v", result)
+	}
+}
+
+func TestCoverRomajiParallelAndIDHSHelpers(t *testing.T) {
+	spotify := "https://i.scdn.co/image/ab67616d00001e02abcdef"
+	if got := GetCoverFromSpotify(spotify, true); !strings.Contains(got, spotifySizeMax) {
+		t.Fatalf("spotify cover = %q", got)
+	}
+	if got := upgradeToMaxQuality("https://cdn-images.dzcdn.net/images/cover/abc/500x500-000000-80-0-0.jpg"); !strings.Contains(got, "1800x1800") {
+		t.Fatalf("deezer cover = %q", got)
+	}
+	if got := upgradeToMaxQuality("https://resources.tidal.com/images/id/320x320.jpg"); !strings.Contains(got, "origin.jpg") {
+		t.Fatalf("tidal cover = %q", got)
+	}
+	if got := upgradeToMaxQuality("https://static.qobuz.com/images/covers/ab/cd/foo_600.jpg"); !strings.Contains(got, "_max.jpg") {
+		t.Fatalf("qobuz cover = %q", got)
+	}
+	if data, err := downloadCoverToMemory("", false); err == nil || data != nil {
+		t.Fatalf("expected empty cover error")
+	}
+
+	if !ContainsJapanese("カタカナ") || ContainsJapanese("abc") {
+		t.Fatal("unexpected Japanese detection")
+	}
+	if got := JapaneseToRomaji("きゃット"); got != "kyatto" {
+		t.Fatalf("romaji = %q", got)
+	}
+	if got := BuildSearchQuery("きゃ! song", "アーティスト"); got != "atisuto kya song" {
+		t.Fatalf("query = %q", got)
+	}
+	if got := CleanToASCII("A, B. C!"); got != "A B C" {
+		t.Fatalf("ascii = %q", got)
+	}
+
+	if err := PreWarmCache(`not-json`); err == nil {
+		t.Fatal("expected prewarm JSON error")
+	}
+	if err := PreWarmCache(`[{"isrc":"ISRC","track_name":"Song","artist_name":"Artist","spotify_id":"sp","service":"tidal"}]`); err != nil {
+		t.Fatalf("PreWarmCache: %v", err)
+	}
+	if result := FetchCoverAndLyricsParallel("", false, "", "", "", false, 0); result == nil || result.CoverErr != nil || result.LyricsErr != nil {
+		t.Fatalf("parallel result = %#v", result)
+	}
+	if ClearTrackCache(); GetCacheSize() != 0 {
+		t.Fatal("expected empty cache size")
+	}
+
+	client := &IDHSClient{client: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+		if req.Method != http.MethodPost {
+			t.Fatalf("method = %s", req.Method)
+		}
+		body := `{"id":"1","type":"song","title":"Song","links":[{"type":"tidal","url":"https://tidal.com/browse/track/7"},{"type":"deezer","url":"https://www.deezer.com/track/9"},{"type":"spotify","url":"https://open.spotify.com/track/abc"}]}`
+		return &http.Response{
+			StatusCode: 200,
+			Header:     make(http.Header),
+			Body:       io.NopCloser(strings.NewReader(body)),
+			Request:    req,
+		}, nil
+	})}}
+	availability, err := client.GetAvailabilityFromSpotify("spotify-track")
+	if err != nil {
+		t.Fatalf("GetAvailabilityFromSpotify: %v", err)
+	}
+	if !availability.Tidal || !availability.Deezer || availability.DeezerID != "9" {
+		t.Fatalf("spotify availability = %#v", availability)
+	}
+	deezerAvailability, err := client.GetAvailabilityFromDeezer("9")
+	if err != nil {
+		t.Fatalf("GetAvailabilityFromDeezer: %v", err)
+	}
+	if deezerAvailability.SpotifyID != "abc" || !deezerAvailability.Tidal {
+		t.Fatalf("deezer availability = %#v", deezerAvailability)
+	}
+
+	errorClient := &IDHSClient{client: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+		return &http.Response{StatusCode: 429, Body: io.NopCloser(strings.NewReader("")), Request: req}, nil
+	})}}
+	if _, err := errorClient.Search("bad", nil); err == nil {
+		t.Fatal("expected rate limit error")
+	}
+}
@@ -10,6 +10,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"time"

 	"github.com/dop251/goja"
 )
@@ -43,41 +44,105 @@ func compareVersions(v1, v2 string) int {
 	return 0
 }

-type LoadedExtension struct {
-	ID        string             `json:"id"`
-	Manifest  *ExtensionManifest `json:"manifest"`
-	VM        *goja.Runtime      `json:"-"`
-	VMMu      sync.Mutex         `json:"-"`
-	runtime   *ExtensionRuntime
-	Enabled   bool   `json:"enabled"`
-	Error     string `json:"error,omitempty"`
-	DataDir   string `json:"data_dir"`
-	SourceDir string `json:"source_dir"`
-	IconPath  string `json:"icon_path"`
+type loadedExtension struct {
+	ID          string             `json:"id"`
+	Manifest    *ExtensionManifest `json:"manifest"`
+	VM          *goja.Runtime      `json:"-"`
+	VMMu        sync.Mutex         `json:"-"`
+	runtime     *extensionRuntime
+	initialized bool
+	Enabled     bool   `json:"enabled"`
+	Error       string `json:"error,omitempty"`
+	DataDir     string `json:"data_dir"`
+	SourceDir   string `json:"source_dir"`
+	IconPath    string `json:"icon_path"`
 }

-type ExtensionManager struct {
-	mu            sync.RWMutex
-	extensions    map[string]*LoadedExtension
+func getExtensionInitSettings(extensionID string) map[string]interface{} {
+	settings := GetExtensionSettingsStore().GetAll(extensionID)
+	if len(settings) == 0 {
+		return settings
+	}
+
+	filtered := make(map[string]interface{}, len(settings))
+	for key, value := range settings {
+		if strings.HasPrefix(key, "_") {
+			continue
+		}
+		filtered[key] = value
+	}
+	return filtered
+}
+
+func ensureRuntimeReadyLocked(ext *loadedExtension, applyStoredSettings bool) error {
+	if ext.VM == nil || ext.runtime == nil {
+		if err := initializeVMLocked(ext); err != nil {
+			ext.Error = err.Error()
+			ext.Enabled = false
+			return err
+		}
+	}
+
+	if applyStoredSettings && !ext.initialized {
+		settings := getExtensionInitSettings(ext.ID)
+		if len(settings) > 0 {
+			if err := initializeExtensionWithSettingsLocked(ext, settings); err != nil {
+				teardownVMLocked(ext)
+				ext.Error = err.Error()
+				ext.Enabled = false
+				return err
+			}
+		} else {
+			ext.initialized = true
+		}
+	}
+
+	ext.Error = ""
+	return nil
+}
+
+func (ext *loadedExtension) ensureRuntimeReady() error {
+	ext.VMMu.Lock()
+	defer ext.VMMu.Unlock()
+
+	return ensureRuntimeReadyLocked(ext, true)
+}
+
+func (ext *loadedExtension) lockReadyVM() (*goja.Runtime, error) {
+	ext.VMMu.Lock()
+	if err := ensureRuntimeReadyLocked(ext, true); err != nil {
+		ext.VMMu.Unlock()
+		return nil, err
+	}
+	return ext.VM, nil
+}
+
+type extensionManager struct {
+	mu sync.RWMutex
+	// mutationMu serializes install/upgrade/remove (heavy FS + goja VM
+	// teardown/reload), which are not safe to run concurrently. Acquired before
+	// m.mu; "*Locked" helpers assume it is held.
+	mutationMu    sync.Mutex
+	extensions    map[string]*loadedExtension
 	extensionsDir string
 	dataDir       string
 }

 var (
-	globalExtManager     *ExtensionManager
+	globalExtManager     *extensionManager
 	globalExtManagerOnce sync.Once
 )

-func GetExtensionManager() *ExtensionManager {
+func getExtensionManager() *extensionManager {
 	globalExtManagerOnce.Do(func() {
-		globalExtManager = &ExtensionManager{
-			extensions: make(map[string]*LoadedExtension),
+		globalExtManager = &extensionManager{
+			extensions: make(map[string]*loadedExtension),
 		}
 	})
 	return globalExtManager
 }

-func (m *ExtensionManager) SetDirectories(extensionsDir, dataDir string) error {
+func (m *extensionManager) SetDirectories(extensionsDir, dataDir string) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()

@@ -94,14 +159,20 @@ func (m *ExtensionManager) SetDirectories(extensionsDir, dataDir string) error {
 	return nil
 }

-func (m *ExtensionManager) LoadExtensionFromFile(filePath string) (*LoadedExtension, error) {
+func (m *extensionManager) LoadExtensionFromFile(filePath string) (*loadedExtension, error) {
+	m.mutationMu.Lock()
+	defer m.mutationMu.Unlock()
+	return m.loadExtensionFromFileLocked(filePath)
+}
+
+func (m *extensionManager) loadExtensionFromFileLocked(filePath string) (*loadedExtension, error) {
 	if !strings.HasSuffix(strings.ToLower(filePath), ".spotiflac-ext") {
-		return nil, fmt.Errorf("Invalid file format. Please select a .spotiflac-ext file")
+		return nil, fmt.Errorf("invalid file format: please select a .spotiflac-ext file")
 	}

 	zipReader, err := zip.OpenReader(filePath)
 	if err != nil {
-		return nil, fmt.Errorf("Cannot open extension file. The file may be corrupted or not a valid extension package")
+		return nil, fmt.Errorf("cannot open extension file: the file may be corrupted or not a valid extension package")
 	}
 	defer zipReader.Close()

@@ -126,16 +197,16 @@ func (m *ExtensionManager) LoadExtensionFromFile(filePath string) (*LoadedExtens
 	}

 	if manifestData == nil {
-		return nil, fmt.Errorf("Invalid extension package: manifest.json not found")
+		return nil, fmt.Errorf("invalid extension package: manifest.json not found")
 	}

 	if !hasIndexJS {
-		return nil, fmt.Errorf("Invalid extension package: index.js not found")
+		return nil, fmt.Errorf("invalid extension package: index.js not found")
 	}

 	manifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid extension manifest: %w", err)
+		return nil, fmt.Errorf("invalid extension manifest: %w", err)
 	}

 	m.mu.RLock()
@@ -151,11 +222,11 @@ func (m *ExtensionManager) LoadExtensionFromFile(filePath string) (*LoadedExtens
 	if exists {
 		versionCompare := compareVersions(manifest.Version, existingVersion)
 		if versionCompare > 0 {
-			return m.UpgradeExtension(filePath)
+			return m.upgradeExtensionLocked(filePath)
 		} else if versionCompare == 0 {
-			return nil, fmt.Errorf("Extension '%s' v%s is already installed", existingDisplayName, existingVersion)
+			return nil, fmt.Errorf("extension '%s' v%s is already installed", existingDisplayName, existingVersion)
 		} else {
-			return nil, fmt.Errorf("Cannot downgrade '%s' from v%s to v%s", existingDisplayName, existingVersion, manifest.Version)
+			return nil, fmt.Errorf("cannot downgrade '%s' from v%s to v%s", existingDisplayName, existingVersion, manifest.Version)
 		}
 	}

@@ -163,7 +234,7 @@ func (m *ExtensionManager) LoadExtensionFromFile(filePath string) (*LoadedExtens
 	defer m.mu.Unlock()

 	if _, exists := m.extensions[manifest.Name]; exists {
-		return nil, fmt.Errorf("Extension '%s' was installed by another process", manifest.DisplayName)
+		return nil, fmt.Errorf("extension '%s' was installed by another process", manifest.DisplayName)
 	}

 	extDir := filepath.Join(m.extensionsDir, manifest.Name)
@@ -212,7 +283,7 @@ func (m *ExtensionManager) LoadExtensionFromFile(filePath string) (*LoadedExtens
 		return nil, fmt.Errorf("failed to create extension data directory: %w", err)
 	}

-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID:        manifest.Name,
 		Manifest:  manifest,
 		Enabled:   false, // New extensions start disabled
@@ -220,10 +291,10 @@ func (m *ExtensionManager) LoadExtensionFromFile(filePath string) (*LoadedExtens
 		SourceDir: extDir,
 	}

-	if err := m.initializeVM(ext); err != nil {
+	if err := validateExtensionLoad(ext); err != nil {
 		ext.Error = err.Error()
 		ext.Enabled = false
-		GoLog("[Extension] Failed to initialize VM for %s: %v\n", manifest.Name, err)
+		GoLog("[Extension] Failed to validate extension %s: %v\n", manifest.Name, err)
 	}

 	m.extensions[manifest.Name] = ext
@@ -232,7 +303,10 @@ func (m *ExtensionManager) LoadExtensionFromFile(filePath string) (*LoadedExtens
 	return ext, nil
 }

-func (m *ExtensionManager) initializeVM(ext *LoadedExtension) error {
+func initializeVMLocked(ext *loadedExtension) error {
+	ext.VM = nil
+	ext.runtime = nil
+	ext.initialized = false
 	vm := goja.New()
 	ext.VM = vm

@@ -242,7 +316,7 @@ func (m *ExtensionManager) initializeVM(ext *LoadedExtension) error {
 		return fmt.Errorf("failed to read index.js: %w", err)
 	}

-	runtime := NewExtensionRuntime(ext)
+	runtime := newExtensionRuntime(ext)
 	ext.runtime = runtime
 	runtime.RegisterAPIs(vm)
 	runtime.RegisterGoBackendAPIs(vm)
@@ -279,30 +353,239 @@ func (m *ExtensionManager) initializeVM(ext *LoadedExtension) error {
 	return nil
 }

-func (m *ExtensionManager) UnloadExtension(extensionID string) error {
+func newIsolatedExtensionRuntime(ext *loadedExtension) (*goja.Runtime, *extensionRuntime, error) {
+	vm := goja.New()
+
+	indexPath := filepath.Join(ext.SourceDir, "index.js")
+	jsCode, err := os.ReadFile(indexPath)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to read index.js: %w", err)
+	}
+
+	runtime := &extensionRuntime{
+		extensionID:       ext.ID,
+		manifest:          ext.Manifest,
+		settings:          make(map[string]interface{}),
+		cookieJar:         nil,
+		dataDir:           ext.DataDir,
+		vm:                vm,
+		storageFlushDelay: defaultStorageFlushDelay,
+	}
+	if ext.runtime != nil && ext.runtime.cookieJar != nil {
+		runtime.cookieJar = ext.runtime.cookieJar
+	} else {
+		jar, _ := newSimpleCookieJar()
+		runtime.cookieJar = jar
+	}
+	runtime.httpClient = newExtensionHTTPClient(ext, runtime.cookieJar, extensionHTTPTimeout(ext, 30*time.Second), true)
+	runtime.downloadClient = newExtensionHTTPClient(ext, runtime.cookieJar, DownloadTimeout, false)
+	runtime.RegisterAPIs(vm)
+	runtime.RegisterGoBackendAPIs(vm)
+
+	console := vm.NewObject()
+	console.Set("log", func(call goja.FunctionCall) goja.Value {
+		args := make([]interface{}, len(call.Arguments))
+		for i, arg := range call.Arguments {
+			args[i] = arg.Export()
+		}
+		GoLog("[Extension:%s] %v\n", ext.ID, args)
+		return goja.Undefined()
+	})
+	vm.Set("console", console)
+
+	var registeredExtension goja.Value
+	vm.Set("registerExtension", func(call goja.FunctionCall) goja.Value {
+		if len(call.Arguments) > 0 {
+			registeredExtension = call.Arguments[0]
+			vm.Set("extension", call.Arguments[0])
+		}
+		return goja.Undefined()
+	})
+
+	if _, err := vm.RunString(string(jsCode)); err != nil {
+		runtime.closeStorageFlusher()
+		return nil, nil, fmt.Errorf("failed to execute extension code: %w", err)
+	}
+
+	if registeredExtension == nil || goja.IsUndefined(registeredExtension) {
+		runtime.closeStorageFlusher()
+		return nil, nil, fmt.Errorf("extension did not call registerExtension()")
+	}
+
+	settings := getExtensionInitSettings(ext.ID)
+	if len(settings) > 0 {
+		if err := initializeExtensionRuntimeWithSettings(vm, ext.ID, settings); err != nil {
+			runtime.closeStorageFlusher()
+			return nil, nil, err
+		}
+	}
+
+	return vm, runtime, nil
+}
+
+func (m *extensionManager) initializeVM(ext *loadedExtension) error {
+	ext.VMMu.Lock()
+	defer ext.VMMu.Unlock()
+	return initializeVMLocked(ext)
+}
+
+func initializeExtensionRuntimeWithSettings(
+	vm *goja.Runtime,
+	extensionID string,
+	settings map[string]interface{},
+) error {
+	settingsJSON, err := json.Marshal(settings)
+	if err != nil {
+		return fmt.Errorf("failed to save settings")
+	}
+
+	script := fmt.Sprintf(`
+		(function() {
+			var settings = %s;
+			if (typeof extension !== 'undefined' && typeof extension.initialize === 'function') {
+				try {
+					extension.initialize(settings);
+					return { success: true };
+				} catch (e) {
+					return { success: false, error: e.toString() };
+				}
+			}
+			return { success: true, message: 'no initialize function' };
+		})()
+	`, string(settingsJSON))
+
+	result, err := vm.RunString(script)
+	if err != nil {
+		GoLog("[Extension] Initialize error for %s: %v\n", extensionID, err)
+		return err
+	}
+
+	if result != nil && !goja.IsUndefined(result) {
+		exported := result.Export()
+		if resultMap, ok := exported.(map[string]interface{}); ok {
+			if success, ok := resultMap["success"].(bool); ok && !success {
+				errMsg := "unknown error"
+				if e, ok := resultMap["error"].(string); ok {
+					errMsg = e
+				}
+				GoLog("[Extension] Initialize failed for %s: %s\n", extensionID, errMsg)
+				return fmt.Errorf("initialize failed: %s", errMsg)
+			}
+		}
+	}
+
+	return nil
+}
+
+func initializeExtensionWithSettingsLocked(
+	ext *loadedExtension,
+	settings map[string]interface{},
+) error {
+	if ext.VM == nil {
+		return fmt.Errorf("extension failed to load: please reinstall the extension")
+	}
+
+	if err := initializeExtensionRuntimeWithSettings(ext.VM, ext.ID, settings); err != nil {
+		ext.Error = err.Error()
+		ext.Enabled = false
+		return err
+	}
+
+	ext.initialized = true
+	GoLog("[Extension] Initialized %s\n", ext.ID)
+	return nil
+}
+
+func runCleanupLocked(ext *loadedExtension) error {
+	if ext.VM != nil {
+		if err := runCleanupOnVM(ext.VM); err != nil {
+			return err
+		}
+		if ext.VM.Get("extension") != nil {
+			GoLog("[Extension] Cleanup called for %s\n", ext.ID)
+		}
+	}
+	return nil
+}
+
+func runCleanupOnVM(vm *goja.Runtime) error {
+	if vm == nil {
+		return nil
+	}
+
+	script := `
+		(function() {
+			if (typeof extension !== 'undefined' && typeof extension.cleanup === 'function') {
+				try {
+					extension.cleanup();
+					return { success: true };
+				} catch (e) {
+					return { success: false, error: e.toString() };
+				}
+			}
+			return { success: true, message: 'no cleanup function' };
+		})()
+	`
+
+	result, err := vm.RunString(script)
+	if err != nil {
+		return err
+	}
+
+	if result != nil && !goja.IsUndefined(result) {
+		exported := result.Export()
+		if resultMap, ok := exported.(map[string]interface{}); ok {
+			if success, ok := resultMap["success"].(bool); ok && !success {
+				errMsg := "unknown error"
+				if e, ok := resultMap["error"].(string); ok {
+					errMsg = e
+				}
+				return fmt.Errorf("cleanup failed: %s", errMsg)
+			}
+		}
+	}
+
+	return nil
+}
+
+func teardownVMLocked(ext *loadedExtension) {
+	if err := runCleanupLocked(ext); err != nil {
+		GoLog("[Extension] Error calling cleanup for %s: %v\n", ext.ID, err)
+	}
+	if ext.runtime != nil {
+		if err := ext.runtime.flushStorageNow(); err != nil {
+			GoLog("[Extension] Failed to flush storage for %s: %v\n", ext.ID, err)
+		}
+		ext.runtime.closeStorageFlusher()
+	}
+	ext.runtime = nil
+	ext.VM = nil
+	ext.initialized = false
+}
+
+func validateExtensionLoad(ext *loadedExtension) error {
+	ext.VMMu.Lock()
+	defer ext.VMMu.Unlock()
+
+	if err := initializeVMLocked(ext); err != nil {
+		return err
+	}
+	teardownVMLocked(ext)
+	return nil
+}
+
+func (m *extensionManager) UnloadExtension(extensionID string) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()

 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}

-	if ext.VM != nil {
-		cleanup, err := ext.VM.RunString("typeof extension !== 'undefined' && typeof extension.cleanup === 'function' ? extension.cleanup() : null")
-		if err != nil {
-			GoLog("[Extension] Error calling cleanup for %s: %v\n", extensionID, err)
-		} else if cleanup != nil && !goja.IsUndefined(cleanup) && !goja.IsNull(cleanup) {
-			GoLog("[Extension] Cleanup called for %s\n", extensionID)
-		}
-	}
-	if ext.runtime != nil {
-		if err := ext.runtime.flushStorageNow(); err != nil {
-			GoLog("[Extension] Failed to flush storage for %s: %v\n", extensionID, err)
-		}
-		ext.runtime.closeStorageFlusher()
-		ext.runtime = nil
-	}
+	ext.VMMu.Lock()
+	teardownVMLocked(ext)
+	ext.VMMu.Unlock()

 	delete(m.extensions, extensionID)
 	GoLog("[Extension] Unloaded extension: %s\n", extensionID)
@@ -310,38 +593,52 @@ func (m *ExtensionManager) UnloadExtension(extensionID string) error {
 	return nil
 }

-func (m *ExtensionManager) GetExtension(extensionID string) (*LoadedExtension, error) {
+func (m *extensionManager) GetExtension(extensionID string) (*loadedExtension, error) {
 	m.mu.RLock()
 	defer m.mu.RUnlock()

 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return nil, fmt.Errorf("Extension not found")
+		return nil, fmt.Errorf("extension not found")
 	}
 	return ext, nil
 }

-func (m *ExtensionManager) GetAllExtensions() []*LoadedExtension {
+func (m *extensionManager) GetAllExtensions() []*loadedExtension {
 	m.mu.RLock()
 	defer m.mu.RUnlock()

-	result := make([]*LoadedExtension, 0, len(m.extensions))
+	result := make([]*loadedExtension, 0, len(m.extensions))
 	for _, ext := range m.extensions {
 		result = append(result, ext)
 	}
 	return result
 }

-func (m *ExtensionManager) SetExtensionEnabled(extensionID string, enabled bool) error {
+func (m *extensionManager) SetExtensionEnabled(extensionID string, enabled bool) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()

 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}

-	ext.Enabled = enabled
+	if enabled {
+		ext.Enabled = true
+		if err := ext.ensureRuntimeReady(); err != nil {
+			store := GetExtensionSettingsStore()
+			ext.Enabled = false
+			_ = store.Set(extensionID, "_enabled", false)
+			return err
+		}
+	} else {
+		ext.Enabled = false
+		ext.Error = ""
+		ext.VMMu.Lock()
+		teardownVMLocked(ext)
+		ext.VMMu.Unlock()
+	}
 	GoLog("[Extension] %s %s\n", extensionID, map[bool]string{true: "enabled", false: "disabled"}[enabled])

 	store := GetExtensionSettingsStore()
@@ -352,7 +649,7 @@ func (m *ExtensionManager) SetExtensionEnabled(extensionID string, enabled bool)
 	return nil
 }

-func (m *ExtensionManager) LoadExtensionsFromDirectory(dirPath string) ([]string, []error) {
+func (m *extensionManager) LoadExtensionsFromDirectory(dirPath string) ([]string, []error) {
 	var loaded []string
 	var errors []error

@@ -390,7 +687,7 @@ func (m *ExtensionManager) LoadExtensionsFromDirectory(dirPath string) ([]string
 	return loaded, errors
 }

-func (m *ExtensionManager) loadExtensionFromDirectory(dirPath string) (*LoadedExtension, error) {
+func (m *extensionManager) loadExtensionFromDirectory(dirPath string) (*loadedExtension, error) {
 	m.mu.Lock()
 	defer m.mu.Unlock()

@@ -402,12 +699,12 @@ func (m *ExtensionManager) loadExtensionFromDirectory(dirPath string) (*LoadedEx

 	manifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid extension manifest: %w", err)
+		return nil, fmt.Errorf("invalid extension manifest: %w", err)
 	}

 	indexPath := filepath.Join(dirPath, "index.js")
 	if _, err := os.Stat(indexPath); os.IsNotExist(err) {
-		return nil, fmt.Errorf("Extension is missing index.js file")
+		return nil, fmt.Errorf("extension is missing index.js file")
 	}

 	if existing, exists := m.extensions[manifest.Name]; exists {
@@ -420,7 +717,7 @@ func (m *ExtensionManager) loadExtensionFromDirectory(dirPath string) (*LoadedEx
 		return nil, fmt.Errorf("failed to create extension data directory: %w", err)
 	}

-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID:        manifest.Name,
 		Manifest:  manifest,
 		Enabled:   false, // Will be restored from settings store
@@ -436,10 +733,10 @@ func (m *ExtensionManager) loadExtensionFromDirectory(dirPath string) (*LoadedEx
 		}
 	}

-	if err := m.initializeVM(ext); err != nil {
+	if err := validateExtensionLoad(ext); err != nil {
 		ext.Error = err.Error()
 		ext.Enabled = false
-		GoLog("[Extension] Failed to initialize VM for %s: %v\n", manifest.Name, err)
+		GoLog("[Extension] Failed to validate extension %s: %v\n", manifest.Name, err)
 	}

 	m.extensions[manifest.Name] = ext
@@ -448,7 +745,10 @@ func (m *ExtensionManager) loadExtensionFromDirectory(dirPath string) (*LoadedEx
 	return ext, nil
 }

-func (m *ExtensionManager) RemoveExtension(extensionID string) error {
+func (m *extensionManager) RemoveExtension(extensionID string) error {
+	m.mutationMu.Lock()
+	defer m.mutationMu.Unlock()
+
 	ext, err := m.GetExtension(extensionID)
 	if err != nil {
 		return err
@@ -468,14 +768,20 @@ func (m *ExtensionManager) RemoveExtension(extensionID string) error {
 }

 // Only allows upgrades (new version > current version), not downgrades
-func (m *ExtensionManager) UpgradeExtension(filePath string) (*LoadedExtension, error) {
+func (m *extensionManager) UpgradeExtension(filePath string) (*loadedExtension, error) {
+	m.mutationMu.Lock()
+	defer m.mutationMu.Unlock()
+	return m.upgradeExtensionLocked(filePath)
+}
+
+func (m *extensionManager) upgradeExtensionLocked(filePath string) (*loadedExtension, error) {
 	if !strings.HasSuffix(strings.ToLower(filePath), ".spotiflac-ext") {
-		return nil, fmt.Errorf("Invalid file format. Please select a .spotiflac-ext file")
+		return nil, fmt.Errorf("invalid file format: please select a .spotiflac-ext file")
 	}

 	zipReader, err := zip.OpenReader(filePath)
 	if err != nil {
-		return nil, fmt.Errorf("Cannot open extension file. The file may be corrupted or not a valid extension package")
+		return nil, fmt.Errorf("cannot open extension file: the file may be corrupted or not a valid extension package")
 	}
 	defer zipReader.Close()

@@ -500,16 +806,16 @@ func (m *ExtensionManager) UpgradeExtension(filePath string) (*LoadedExtension,
 	}

 	if manifestData == nil {
-		return nil, fmt.Errorf("Invalid extension package: manifest.json not found")
+		return nil, fmt.Errorf("invalid extension package: manifest.json not found")
 	}

 	if !hasIndexJS {
-		return nil, fmt.Errorf("Invalid extension package: index.js not found")
+		return nil, fmt.Errorf("invalid extension package: index.js not found")
 	}

 	newManifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid extension manifest: %w", err)
+		return nil, fmt.Errorf("invalid extension manifest: %w", err)
 	}

 	m.mu.RLock()
@@ -517,15 +823,15 @@ func (m *ExtensionManager) UpgradeExtension(filePath string) (*LoadedExtension,
 	m.mu.RUnlock()

 	if !exists {
-		return nil, fmt.Errorf("Extension '%s' is not installed. Use install instead of upgrade.", newManifest.DisplayName)
+		return nil, fmt.Errorf("extension '%s' is not installed; use install instead of upgrade", newManifest.DisplayName)
 	}

 	versionCompare := compareVersions(newManifest.Version, existing.Manifest.Version)
 	if versionCompare < 0 {
-		return nil, fmt.Errorf("Cannot downgrade extension. Current version: %s, New version: %s", existing.Manifest.Version, newManifest.Version)
+		return nil, fmt.Errorf("cannot downgrade extension: current version: %s, new version: %s", existing.Manifest.Version, newManifest.Version)
 	}
 	if versionCompare == 0 {
-		return nil, fmt.Errorf("Extension is already at version %s", existing.Manifest.Version)
+		return nil, fmt.Errorf("extension is already at version %s", existing.Manifest.Version)
 	}

 	GoLog("[Extension] Upgrading %s from v%s to v%s\n", newManifest.DisplayName, existing.Manifest.Version, newManifest.Version)
@@ -582,7 +888,7 @@ func (m *ExtensionManager) UpgradeExtension(filePath string) (*LoadedExtension,
 		}
 	}

-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID:        newManifest.Name,
 		Manifest:  newManifest,
 		Enabled:   wasEnabled, // Preserve enabled state from before upgrade
@@ -590,10 +896,14 @@ func (m *ExtensionManager) UpgradeExtension(filePath string) (*LoadedExtension,
 		SourceDir: extDir,
 	}

-	if err := m.initializeVM(ext); err != nil {
+	if wasEnabled {
+		if err := ext.ensureRuntimeReady(); err != nil {
+			GoLog("[Extension] Failed to initialize upgraded extension %s: %v\n", newManifest.Name, err)
+		}
+	} else if err := validateExtensionLoad(ext); err != nil {
 		ext.Error = err.Error()
 		ext.Enabled = false
-		GoLog("[Extension] Failed to initialize VM for %s: %v\n", newManifest.Name, err)
+		GoLog("[Extension] Failed to validate upgraded extension %s: %v\n", newManifest.Name, err)
 	}

 	m.mu.Lock()
@@ -613,15 +923,15 @@ type ExtensionUpgradeInfo struct {
 	IsInstalled    bool   `json:"is_installed"`
 }

-func (m *ExtensionManager) checkExtensionUpgradeInternal(filePath string) (*ExtensionUpgradeInfo, error) {
+func (m *extensionManager) checkExtensionUpgradeInternal(filePath string) (*ExtensionUpgradeInfo, error) {
 	if !strings.HasSuffix(strings.ToLower(filePath), ".spotiflac-ext") {
-		return nil, fmt.Errorf("Invalid file format. Please select a .spotiflac-ext file")
+		return nil, fmt.Errorf("invalid file format: please select a .spotiflac-ext file")
 	}

 	zipReader, err := zip.OpenReader(filePath)

 	if err != nil {
-		return nil, fmt.Errorf("Cannot open extension file")
+		return nil, fmt.Errorf("cannot open extension file")
 	}
 	defer zipReader.Close()

@@ -648,7 +958,7 @@ func (m *ExtensionManager) checkExtensionUpgradeInternal(filePath string) (*Exte

 	newManifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid manifest: %w", err)
+		return nil, fmt.Errorf("invalid manifest: %w", err)
 	}

 	m.mu.RLock()
@@ -672,7 +982,7 @@ func (m *ExtensionManager) checkExtensionUpgradeInternal(filePath string) (*Exte
 	return info, nil
 }

-func (m *ExtensionManager) CheckExtensionUpgradeJSON(filePath string) (string, error) {
+func (m *extensionManager) CheckExtensionUpgradeJSON(filePath string) (string, error) {
 	info, err := m.checkExtensionUpgradeInternal(filePath)
 	if err != nil {
 		return "", err
@@ -686,7 +996,7 @@ func (m *ExtensionManager) CheckExtensionUpgradeJSON(filePath string) (string, e
 	return string(jsonBytes), nil
 }

-func (m *ExtensionManager) GetInstalledExtensionsJSON() (string, error) {
+func (m *extensionManager) GetInstalledExtensionsJSON() (string, error) {
 	extensions := m.GetAllExtensions()

 	type ExtensionInfo struct {
@@ -694,7 +1004,6 @@ func (m *ExtensionManager) GetInstalledExtensionsJSON() (string, error) {
 		Name                   string                 `json:"name"`
 		DisplayName            string                 `json:"display_name"`
 		Version                string                 `json:"version"`
-		Author                 string                 `json:"author"`
 		Description            string                 `json:"description"`
 		Homepage               string                 `json:"homepage,omitempty"`
 		IconPath               string                 `json:"icon_path,omitempty"`
@@ -709,9 +1018,12 @@ func (m *ExtensionManager) GetInstalledExtensionsJSON() (string, error) {
 		HasDownloadProvider    bool                   `json:"has_download_provider"`
 		HasLyricsProvider      bool                   `json:"has_lyrics_provider"`
 		SkipMetadataEnrichment bool                   `json:"skip_metadata_enrichment"`
+		SkipLyrics             bool                   `json:"skip_lyrics"`
+		StopProviderFallback   bool                   `json:"stop_provider_fallback"`
 		SearchBehavior         *SearchBehaviorConfig  `json:"search_behavior,omitempty"`
 		TrackMatching          *TrackMatchingConfig   `json:"track_matching,omitempty"`
 		PostProcessing         *PostProcessingConfig  `json:"post_processing,omitempty"`
+		ServiceHealth          []ExtensionHealthCheck `json:"service_health,omitempty"`
 		Capabilities           map[string]interface{} `json:"capabilities,omitempty"`
 	}

@@ -751,7 +1063,6 @@ func (m *ExtensionManager) GetInstalledExtensionsJSON() (string, error) {
 			Name:                   ext.Manifest.Name,
 			DisplayName:            ext.Manifest.DisplayName,
 			Version:                ext.Manifest.Version,
-			Author:                 ext.Manifest.Author,
 			Description:            ext.Manifest.Description,
 			Homepage:               ext.Manifest.Homepage,
 			IconPath:               iconPath,
@@ -766,9 +1077,12 @@ func (m *ExtensionManager) GetInstalledExtensionsJSON() (string, error) {
 			HasDownloadProvider:    ext.Manifest.IsDownloadProvider(),
 			HasLyricsProvider:      ext.Manifest.IsLyricsProvider(),
 			SkipMetadataEnrichment: ext.Manifest.SkipMetadataEnrichment,
+			SkipLyrics:             ext.Manifest.SkipLyrics,
+			StopProviderFallback:   ext.Manifest.StopsProviderFallback(),
 			SearchBehavior:         ext.Manifest.SearchBehavior,
 			TrackMatching:          ext.Manifest.TrackMatching,
 			PostProcessing:         ext.Manifest.PostProcessing,
+			ServiceHealth:          ext.Manifest.ServiceHealth,
 			Capabilities:           ext.Manifest.Capabilities,
 		}
 	}
@@ -781,119 +1095,47 @@ func (m *ExtensionManager) GetInstalledExtensionsJSON() (string, error) {
 	return string(jsonBytes), nil
 }

-func (m *ExtensionManager) InitializeExtension(extensionID string, settings map[string]interface{}) error {
+func (m *extensionManager) InitializeExtension(extensionID string, settings map[string]interface{}) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()

 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}

-	if ext.VM == nil {
-		return fmt.Errorf("Extension failed to load. Please reinstall the extension")
-	}
+	ext.VMMu.Lock()
+	defer ext.VMMu.Unlock()

-	settingsJSON, err := json.Marshal(settings)
-	if err != nil {
-		return fmt.Errorf("Failed to save settings")
-	}
-
-	script := fmt.Sprintf(`
-		(function() {
-			var settings = %s;
-			if (typeof extension !== 'undefined' && typeof extension.initialize === 'function') {
-				try {
-					extension.initialize(settings);
-					return { success: true };
-				} catch (e) {
-					return { success: false, error: e.toString() };
-				}
-			}
-			return { success: true, message: 'no initialize function' };
-		})()
-	`, string(settingsJSON))
-
-	result, err := ext.VM.RunString(script)
-	if err != nil {
-		ext.Error = fmt.Sprintf("initialize failed: %v", err)
-		ext.Enabled = false
-		GoLog("[Extension] Initialize error for %s: %v\n", extensionID, err)
+	if err := ensureRuntimeReadyLocked(ext, false); err != nil {
 		return err
 	}
-
-	if result != nil && !goja.IsUndefined(result) {
-		exported := result.Export()
-		if resultMap, ok := exported.(map[string]interface{}); ok {
-			if success, ok := resultMap["success"].(bool); ok && !success {
-				errMsg := "unknown error"
-				if e, ok := resultMap["error"].(string); ok {
-					errMsg = e
-				}
-				ext.Error = errMsg
-				ext.Enabled = false
-				GoLog("[Extension] Initialize failed for %s: %s\n", extensionID, errMsg)
-				return fmt.Errorf("initialize failed: %s", errMsg)
-			}
-		}
-	}
-
-	GoLog("[Extension] Initialized %s\n", extensionID)
-	return nil
+	return initializeExtensionWithSettingsLocked(ext, settings)
 }

-func (m *ExtensionManager) CleanupExtension(extensionID string) error {
+func (m *extensionManager) CleanupExtension(extensionID string) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()

 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}

 	if ext.VM == nil {
 		return nil
 	}
-
-	script := `
-		(function() {
-			if (typeof extension !== 'undefined' && typeof extension.cleanup === 'function') {
-				try {
-					extension.cleanup();
-					return { success: true };
-				} catch (e) {
-					return { success: false, error: e.toString() };
-				}
-			}
-			return { success: true, message: 'no cleanup function' };
-		})()
-	`
-
-	result, err := ext.VM.RunString(script)
-	if err != nil {
+	ext.VMMu.Lock()
+	defer ext.VMMu.Unlock()
+	if err := runCleanupLocked(ext); err != nil {
 		GoLog("[Extension] Cleanup error for %s: %v\n", extensionID, err)
 		return err
 	}
-
-	if result != nil && !goja.IsUndefined(result) {
-		exported := result.Export()
-		if resultMap, ok := exported.(map[string]interface{}); ok {
-			if success, ok := resultMap["success"].(bool); ok && !success {
-				errMsg := "unknown error"
-				if e, ok := resultMap["error"].(string); ok {
-					errMsg = e
-				}
-				GoLog("[Extension] Cleanup failed for %s: %s\n", extensionID, errMsg)
-				return fmt.Errorf("cleanup failed: %s", errMsg)
-			}
-		}
-	}
-
 	GoLog("[Extension] Cleaned up %s\n", extensionID)
 	return nil
 }

-func (m *ExtensionManager) UnloadAllExtensions() {
+func (m *extensionManager) UnloadAllExtensions() {
 	m.mu.Lock()
 	extensionIDs := make([]string, 0, len(m.extensions))
 	for id := range m.extensions {
@@ -908,7 +1150,7 @@ func (m *ExtensionManager) UnloadAllExtensions() {
 	GoLog("[Extension] All extensions unloaded\n")
 }

-func (m *ExtensionManager) InvokeAction(extensionID string, actionName string) (map[string]interface{}, error) {
+func (m *extensionManager) InvokeAction(extensionID string, actionName string) (map[string]interface{}, error) {
 	m.mu.Lock()
 	defer m.mu.Unlock()

@@ -917,23 +1159,38 @@ func (m *ExtensionManager) InvokeAction(extensionID string, actionName string) (
 		return nil, fmt.Errorf("extension not found: %s", extensionID)
 	}

-	if ext.VM == nil {
-		return nil, fmt.Errorf("extension VM not initialized")
-	}
-
 	if !ext.Enabled {
 		return nil, fmt.Errorf("extension is disabled")
 	}
+	vm, err := ext.lockReadyVM()
+	if err != nil {
+		return nil, err
+	}
+	defer ext.VMMu.Unlock()

+	// Merge extension return values onto the top-level JSON object so Flutter can read
+	// message, open_auth_url, setting_updates without unwrapping a nested "result" key.
 	script := fmt.Sprintf(`
 		(function() {
 			if (typeof extension !== 'undefined' && typeof extension.%s === 'function') {
 				try {
 					var result = extension.%s();
 					if (result && typeof result.then === 'function') {
-						// Handle promise - return pending status
 						return { success: true, pending: true, message: 'Action started' };
 					}
+					if (result !== null && result !== undefined && typeof result === 'object') {
+						var isArr = false;
+						if (typeof Array !== 'undefined' && Array.isArray) {
+							isArr = Array.isArray(result);
+						}
+						if (!isArr) {
+							var out = { success: true };
+							for (var k in result) {
+								out[k] = result[k];
+							}
+							return out;
+						}
+					}
 					return { success: true, result: result };
 				} catch (e) {
 					return { success: false, error: e.toString() };
@@ -943,7 +1200,7 @@ func (m *ExtensionManager) InvokeAction(extensionID string, actionName string) (
 		})()
 	`, actionName, actionName, actionName)

-	result, err := RunWithTimeoutAndRecover(ext.VM, script, DefaultJSTimeout)
+	result, err := RunWithTimeoutAndRecover(vm, script, DefaultJSTimeout)
 	if err != nil {
 		GoLog("[Extension] InvokeAction error for %s.%s: %v\n", extensionID, actionName, err)
 		return nil, fmt.Errorf("action failed: %v", err)
@@ -0,0 +1,143 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestExtensionManagerPackageLifecycle(t *testing.T) {
+	dir := t.TempDir()
+	extensionsDir := filepath.Join(dir, "extensions")
+	dataDir := filepath.Join(dir, "data")
+	manager := &extensionManager{extensions: map[string]*loadedExtension{}}
+	if err := manager.SetDirectories(extensionsDir, dataDir); err != nil {
+		t.Fatalf("SetDirectories: %v", err)
+	}
+	if err := GetExtensionSettingsStore().SetDataDir(dataDir); err != nil {
+		t.Fatalf("settings data dir: %v", err)
+	}
+
+	js := `
+var cleaned = false;
+registerExtension({
+  initialize: function(settings) { this.settings = settings || {}; },
+  cleanup: function() { cleaned = true; },
+  doAction: function() { return { message: "done", setting_updates: { quality: "lossless" } }; },
+  getHomeFeed: function() { return [{ id: "home", title: "Home" }]; },
+  getBrowseCategories: function() { return [{ id: "cat", title: "Category" }]; },
+  searchTracks: function() { return { tracks: [], total: 0 }; },
+  fetchLyrics: function() { return { syncType: "UNSYNCED", lines: [{ words: "hello" }] }; },
+  getDownloadUrl: function() { return { url: "https://example.test/a.flac" }; }
+});
+`
+	pkgV1 := filepath.Join(dir, "manager-ext-v1.spotiflac-ext")
+	createTestExtensionPackage(t, pkgV1, "manager-ext", "1.0.0", js, map[string]string{"../unsafe.txt": "skip"})
+	pkgV2 := filepath.Join(dir, "manager-ext-v2.spotiflac-ext")
+	createTestExtensionPackage(t, pkgV2, "manager-ext", "1.1.0", js, nil)
+
+	if compareVersions("v1.2.0", "1.1.9") <= 0 || compareVersions("1.0.0", "1.0") != 0 || compareVersions("1.0.0", "1.0.1") >= 0 {
+		t.Fatal("compareVersions mismatch")
+	}
+	if _, err := manager.LoadExtensionFromFile(filepath.Join(dir, "bad.txt")); err == nil {
+		t.Fatal("expected bad extension suffix error")
+	}
+	if _, err := manager.LoadExtensionFromFile(filepath.Join(dir, "missing.spotiflac-ext")); err == nil {
+		t.Fatal("expected invalid package error")
+	}
+
+	ext, err := manager.LoadExtensionFromFile(pkgV1)
+	if err != nil {
+		t.Fatalf("LoadExtensionFromFile: %v", err)
+	}
+	if ext.ID != "manager-ext" || ext.Enabled || ext.SourceDir == "" {
+		t.Fatalf("loaded extension = %#v", ext)
+	}
+	if _, err := os.Stat(filepath.Join(ext.SourceDir, "unsafe.txt")); err == nil {
+		t.Fatal("unsafe archive path should not be extracted")
+	}
+	if _, err := manager.LoadExtensionFromFile(pkgV1); err == nil {
+		t.Fatal("expected duplicate version error")
+	}
+
+	installedJSON, err := manager.GetInstalledExtensionsJSON()
+	if err != nil || !strings.Contains(installedJSON, "manager-ext") || !strings.Contains(installedJSON, "icon_path") {
+		t.Fatalf("GetInstalledExtensionsJSON = %q/%v", installedJSON, err)
+	}
+	var installed []map[string]interface{}
+	if err := json.Unmarshal([]byte(installedJSON), &installed); err != nil || len(installed) != 1 {
+		t.Fatalf("decode installed = %#v/%v", installed, err)
+	}
+
+	if err := GetExtensionSettingsStore().Set("manager-ext", "quality", "lossless"); err != nil {
+		t.Fatalf("settings Set: %v", err)
+	}
+	if err := manager.SetExtensionEnabled("manager-ext", true); err != nil {
+		t.Fatalf("enable extension: %v", err)
+	}
+	if !ext.Enabled || ext.VM == nil || !ext.initialized {
+		t.Fatalf("enabled extension = %#v", ext)
+	}
+	if err := manager.InitializeExtension("manager-ext", map[string]interface{}{"quality": "hires"}); err != nil {
+		t.Fatalf("InitializeExtension: %v", err)
+	}
+	action, err := manager.InvokeAction("manager-ext", "doAction")
+	if err != nil || action["success"] != true || action["message"] != "done" {
+		t.Fatalf("InvokeAction = %#v/%v", action, err)
+	}
+	if err := manager.CleanupExtension("manager-ext"); err != nil {
+		t.Fatalf("CleanupExtension: %v", err)
+	}
+	if err := manager.SetExtensionEnabled("manager-ext", false); err != nil {
+		t.Fatalf("disable extension: %v", err)
+	}
+	if ext.VM != nil || ext.initialized {
+		t.Fatalf("expected VM teardown, got %#v", ext)
+	}
+	if _, err := manager.InvokeAction("manager-ext", "doAction"); err == nil {
+		t.Fatal("expected disabled action error")
+	}
+
+	upgradeJSON, err := manager.CheckExtensionUpgradeJSON(pkgV2)
+	if err != nil || !strings.Contains(upgradeJSON, `"can_upgrade":true`) {
+		t.Fatalf("CheckExtensionUpgradeJSON = %q/%v", upgradeJSON, err)
+	}
+	upgraded, err := manager.UpgradeExtension(pkgV2)
+	if err != nil {
+		t.Fatalf("UpgradeExtension: %v", err)
+	}
+	if upgraded.Manifest.Version != "1.1.0" {
+		t.Fatalf("upgraded = %#v", upgraded.Manifest)
+	}
+	if _, err := manager.UpgradeExtension(pkgV1); err == nil {
+		t.Fatal("expected downgrade error")
+	}
+	if err := manager.RemoveExtension("manager-ext"); err != nil {
+		t.Fatalf("RemoveExtension: %v", err)
+	}
+	if _, err := manager.GetExtension("manager-ext"); err == nil {
+		t.Fatal("expected removed extension missing")
+	}
+
+	dirExt := filepath.Join(extensionsDir, "dir-ext")
+	if err := os.MkdirAll(dirExt, 0755); err != nil {
+		t.Fatal(err)
+	}
+	manifest := `{"name":"dir-ext","displayName":"dir-ext","version":"1.0.0","description":"Directory extension","type":["metadata_provider"],"permissions":{}}`
+	if err := os.WriteFile(filepath.Join(dirExt, "manifest.json"), []byte(manifest), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dirExt, "index.js"), []byte(`registerExtension({searchTracks:function(){return {tracks:[], total:0};}});`), 0600); err != nil {
+		t.Fatal(err)
+	}
+	loaded, loadErrs := manager.LoadExtensionsFromDirectory(extensionsDir)
+	if len(loadErrs) != 0 || len(loaded) != 1 || loaded[0] != "dir-ext" {
+		t.Fatalf("LoadExtensionsFromDirectory = %#v/%#v", loaded, loadErrs)
+	}
+	manager.UnloadAllExtensions()
+	if len(manager.GetAllExtensions()) != 0 {
+		t.Fatal("expected all extensions unloaded")
+	}
+}
@@ -25,9 +25,10 @@ const (
 )

 type ExtensionPermissions struct {
-	Network []string `json:"network"`
-	Storage bool     `json:"storage"`
-	File    bool     `json:"file"`
+	Network   []string `json:"network"`
+	Storage   bool     `json:"storage"`
+	File      bool     `json:"file"`
+	AllowHTTP bool     `json:"allowHttp,omitempty"`
 }

 type ExtensionSetting struct {
@@ -101,11 +102,21 @@ type PostProcessingConfig struct {
 	Hooks   []PostProcessingHook `json:"hooks,omitempty"`
 }

+type ExtensionHealthCheck struct {
+	ID              string `json:"id"`
+	Label           string `json:"label,omitempty"`
+	URL             string `json:"url"`
+	Method          string `json:"method,omitempty"`
+	ServiceKey      string `json:"serviceKey,omitempty"`
+	TimeoutMs       int    `json:"timeoutMs,omitempty"`
+	CacheTTLSeconds int    `json:"cacheTtlSeconds,omitempty"`
+	Required        bool   `json:"required,omitempty"`
+}
+
 type ExtensionManifest struct {
 	Name                   string                 `json:"name"`
 	DisplayName            string                 `json:"displayName"`
 	Version                string                 `json:"version"`
-	Author                 string                 `json:"author"`
 	Description            string                 `json:"description"`
 	Homepage               string                 `json:"homepage,omitempty"`
 	Icon                   string                 `json:"icon,omitempty"`
@@ -115,11 +126,14 @@ type ExtensionManifest struct {
 	QualityOptions         []QualityOption        `json:"qualityOptions,omitempty"`
 	MinAppVersion          string                 `json:"minAppVersion,omitempty"`
 	SkipMetadataEnrichment bool                   `json:"skipMetadataEnrichment,omitempty"`
+	SkipLyrics             bool                   `json:"skipLyrics,omitempty"`
+	StopProviderFallback   bool                   `json:"stopProviderFallback,omitempty"`
 	SkipBuiltInFallback    bool                   `json:"skipBuiltInFallback,omitempty"`
 	SearchBehavior         *SearchBehaviorConfig  `json:"searchBehavior,omitempty"`
 	URLHandler             *URLHandlerConfig      `json:"urlHandler,omitempty"`
 	TrackMatching          *TrackMatchingConfig   `json:"trackMatching,omitempty"`
 	PostProcessing         *PostProcessingConfig  `json:"postProcessing,omitempty"`
+	ServiceHealth          []ExtensionHealthCheck `json:"serviceHealth,omitempty"`
 	Capabilities           map[string]interface{} `json:"capabilities,omitempty"`
 }

@@ -154,10 +168,6 @@ func (m *ExtensionManifest) Validate() error {
 		return &ManifestValidationError{Field: "version", Message: "version is required"}
 	}

-	if strings.TrimSpace(m.Author) == "" {
-		return &ManifestValidationError{Field: "author", Message: "author is required"}
-	}
-
 	if strings.TrimSpace(m.Description) == "" {
 		return &ManifestValidationError{Field: "description", Message: "description is required"}
 	}
@@ -206,6 +216,28 @@ func (m *ExtensionManifest) Validate() error {
 		}
 	}

+	for i, check := range m.ServiceHealth {
+		if strings.TrimSpace(check.ID) == "" {
+			return &ManifestValidationError{
+				Field:   fmt.Sprintf("serviceHealth[%d].id", i),
+				Message: "health check id is required",
+			}
+		}
+		if strings.TrimSpace(check.URL) == "" {
+			return &ManifestValidationError{
+				Field:   fmt.Sprintf("serviceHealth[%d].url", i),
+				Message: "health check url is required",
+			}
+		}
+		method := strings.ToUpper(strings.TrimSpace(check.Method))
+		if method != "" && method != "GET" && method != "HEAD" {
+			return &ManifestValidationError{
+				Field:   fmt.Sprintf("serviceHealth[%d].method", i),
+				Message: "health check method must be GET or HEAD",
+			}
+		}
+	}
+
 	return nil
 }

@@ -230,6 +262,13 @@ func (m *ExtensionManifest) IsLyricsProvider() bool {
 	return m.HasType(ExtensionTypeLyricsProvider)
 }

+func (m *ExtensionManifest) StopsProviderFallback() bool {
+	if m == nil {
+		return false
+	}
+	return m.StopProviderFallback || m.SkipBuiltInFallback
+}
+
 func (m *ExtensionManifest) IsDomainAllowed(domain string) bool {
 	domain = strings.ToLower(strings.TrimSpace(domain))
 	for _, allowed := range m.Permissions.Network {
@@ -0,0 +1,119 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"time"
+
+	"github.com/dop251/goja"
+)
+
+type extensionCallPerf struct {
+	extensionID  string
+	operation    string
+	startedAt    time.Time
+	initMs       float64
+	jsMs         float64
+	parseMs      float64
+	items        int
+	payloadBytes int
+}
+
+func newExtensionCallPerf(extensionID, operation string) *extensionCallPerf {
+	if !GetLogBuffer().IsLoggingEnabled() {
+		return nil
+	}
+	return &extensionCallPerf{
+		extensionID: extensionID,
+		operation:   operation,
+		startedAt:   time.Now(),
+	}
+}
+
+func extensionDurationMs(duration time.Duration) float64 {
+	return float64(duration.Microseconds()) / 1000.0
+}
+
+func (p *extensionCallPerf) recordInit(duration time.Duration) {
+	if p == nil {
+		return
+	}
+	p.initMs += extensionDurationMs(duration)
+}
+
+func (p *extensionCallPerf) recordJS(duration time.Duration) {
+	if p == nil {
+		return
+	}
+	p.jsMs += extensionDurationMs(duration)
+}
+
+func (p *extensionCallPerf) recordParse(duration time.Duration) {
+	if p == nil {
+		return
+	}
+	p.parseMs += extensionDurationMs(duration)
+}
+
+func (p *extensionCallPerf) recordPayload(value goja.Value) {
+	if p == nil || gojaValueIsEmpty(value) {
+		return
+	}
+	if payload, err := json.Marshal(value); err == nil {
+		p.payloadBytes = len(payload)
+	}
+}
+
+func (p *extensionCallPerf) setPayloadBytes(payloadBytes int) {
+	if p == nil {
+		return
+	}
+	p.payloadBytes = payloadBytes
+}
+
+func (p *extensionCallPerf) setItems(items int) {
+	if p == nil {
+		return
+	}
+	p.items = items
+}
+
+func (p *extensionCallPerf) finish() {
+	if p == nil {
+		return
+	}
+	LogDebug(
+		"ExtensionPerf",
+		"extension=%s op=%s totalMs=%.1f initMs=%.1f jsMs=%.1f parseMs=%.1f items=%d payloadBytes=%d",
+		p.extensionID,
+		p.operation,
+		extensionDurationMs(time.Since(p.startedAt)),
+		p.initMs,
+		p.jsMs,
+		p.parseMs,
+		p.items,
+		p.payloadBytes,
+	)
+}
+
+func countExtensionTopLevelItems(vm *goja.Runtime, value goja.Value) int {
+	if gojaValueIsEmpty(value) {
+		return 0
+	}
+
+	if length, err := gojaArrayLength(value, vm); err == nil && length > 0 {
+		return length
+	}
+
+	obj := value.ToObject(vm)
+	for _, key := range []string{"items", "tracks", "sections", "albums", "artists", "playlists", "results"} {
+		child := obj.Get(key)
+		if gojaValueIsEmpty(child) {
+			continue
+		}
+		if length, err := gojaArrayLength(child, vm); err == nil && length > 0 {
+			return length
+		}
+	}
+
+	return 1
+}
@@ -0,0 +1,164 @@
+package gobackend
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestExtensionProviderWrapperFullSurface(t *testing.T) {
+	ext := newTestLoadedExtension(t, ExtensionTypeMetadataProvider, ExtensionTypeDownloadProvider, ExtensionTypeLyricsProvider)
+	provider := newExtensionProviderWrapper(ext)
+
+	search, err := provider.SearchTracks("query", 5)
+	if err != nil {
+		t.Fatalf("SearchTracks: %v", err)
+	}
+	if search.Total != 1 || search.Tracks[0].ProviderID != ext.ID || search.Tracks[0].ExternalLinks["tidal"] == "" {
+		t.Fatalf("search = %#v", search)
+	}
+
+	track, err := provider.GetTrack("track-1")
+	if err != nil {
+		t.Fatalf("GetTrack: %v", err)
+	}
+	if track.Name != "Track track-1" || track.ProviderID != ext.ID || track.AudioQuality == "" {
+		t.Fatalf("track = %#v", track)
+	}
+
+	album, err := provider.GetAlbum("album-1")
+	if err != nil {
+		t.Fatalf("GetAlbum: %v", err)
+	}
+	if album.ProviderID != ext.ID || len(album.Tracks) != 1 || album.Tracks[0].ProviderID != ext.ID {
+		t.Fatalf("album = %#v", album)
+	}
+
+	playlist, err := provider.GetPlaylist("playlist-1")
+	if err != nil {
+		t.Fatalf("GetPlaylist: %v", err)
+	}
+	if playlist.Name != "Playlist playlist-1" || playlist.ProviderID != ext.ID {
+		t.Fatalf("playlist = %#v", playlist)
+	}
+
+	artist, err := provider.GetArtist("artist-1")
+	if err != nil {
+		t.Fatalf("GetArtist: %v", err)
+	}
+	if artist.ProviderID != ext.ID || len(artist.Releases) != 1 || artist.Releases[0].ProviderID != ext.ID {
+		t.Fatalf("artist = %#v", artist)
+	}
+
+	enriched, err := provider.EnrichTrack(&ExtTrackMetadata{ID: "track-1", Name: "Old", ProviderID: ext.ID})
+	if err != nil {
+		t.Fatalf("EnrichTrack: %v", err)
+	}
+	if enriched.Name != "Enriched" || enriched.ProviderID != ext.ID {
+		t.Fatalf("enriched = %#v", enriched)
+	}
+
+	availability, err := provider.CheckAvailability("ISRC", "Song", "Artist", "spotify:1", "dz", "tidal", "qobuz")
+	if err != nil {
+		t.Fatalf("CheckAvailability: %v", err)
+	}
+	if !availability.Available || availability.TrackID != "download-track" || !availability.SkipFallback {
+		t.Fatalf("availability = %#v", availability)
+	}
+
+	downloadURL, err := provider.GetDownloadURL("track-1", "LOSSLESS")
+	if err != nil {
+		t.Fatalf("GetDownloadURL: %v", err)
+	}
+	if downloadURL.Format != "flac" || downloadURL.BitDepth != 24 || downloadURL.SampleRate != 96000 {
+		t.Fatalf("download URL = %#v", downloadURL)
+	}
+
+	progress := []int{}
+	download, err := provider.Download("track-1", "LOSSLESS", filepath.Join(t.TempDir(), "song.flac"), "", func(percent int) {
+		progress = append(progress, percent)
+	})
+	if err != nil {
+		t.Fatalf("Download: %v", err)
+	}
+	if !download.Success || download.Decryption == nil || download.DecryptionKey != "001122" || len(progress) != 1 || progress[0] != 100 {
+		t.Fatalf("download = %#v progress=%v", download, progress)
+	}
+
+	lyrics, err := provider.FetchLyrics("Song", "Artist", "Album", 180)
+	if err != nil {
+		t.Fatalf("GetLyrics: %v", err)
+	}
+	if lyrics.Provider != ext.ID || len(lyrics.Lines) != 1 || lyrics.Lines[0].Words != "Hello" {
+		t.Fatalf("lyrics = %#v", lyrics)
+	}
+
+	urlResult, err := provider.HandleURL("https://example.test/track/1")
+	if err != nil {
+		t.Fatalf("HandleURL: %v", err)
+	}
+	if urlResult.Track == nil || urlResult.Track.Name == "" || len(urlResult.Tracks) != 1 || urlResult.Album == nil || urlResult.Artist == nil {
+		t.Fatalf("url result = %#v", urlResult)
+	}
+
+	match, err := provider.MatchTrack(
+		map[string]interface{}{"name": "Song", "artists": "Artist"},
+		[]map[string]interface{}{{"id": "download-track", "name": "Song"}},
+	)
+	if err != nil {
+		t.Fatalf("MatchTrack: %v", err)
+	}
+	if !match.Matched || match.TrackID != "download-track" {
+		t.Fatalf("match = %#v", match)
+	}
+
+	post, err := provider.PostProcess(filepath.Join(t.TempDir(), "song.flac"), map[string]interface{}{"title": "Song"}, "hook")
+	if err != nil {
+		t.Fatalf("PostProcess: %v", err)
+	}
+	if !post.Success || post.BitDepth != 24 || post.SampleRate != 96000 {
+		t.Fatalf("post = %#v", post)
+	}
+}
+
+func TestExtensionProviderAndManagerSelectionHelpers(t *testing.T) {
+	manifest := &ExtensionManifest{Capabilities: map[string]interface{}{
+		"replacesBuiltInProviders": []interface{}{" Deezer ", 7, ""},
+	}}
+	if values := manifestCapabilityStringList(manifest, "replacesBuiltInProviders"); len(values) != 1 || values[0] != "deezer" {
+		t.Fatalf("capability list = %#v", values)
+	}
+	if !extensionReplacesBuiltInProvider(&loadedExtension{Manifest: manifest}, "deezer") || extensionReplacesBuiltInProvider(nil, "deezer") {
+		t.Fatal("extension replacement mismatch")
+	}
+	if trimKnownProviderPrefix("Deezer:101", "deezer") != "101" || trimKnownProviderPrefix("101", "deezer") != "101" {
+		t.Fatal("trimKnownProviderPrefix mismatch")
+	}
+	if metadataTrackDedupKey(ExtTrackMetadata{ISRC: "usrc"}) != "isrc:USRC" ||
+		metadataTrackDedupKey(ExtTrackMetadata{SpotifyID: "sp"}) != "spotify:sp" ||
+		metadataTrackDedupKey(ExtTrackMetadata{ProviderID: "p", ID: "1"}) != "p:1" {
+		t.Fatal("metadata dedup key mismatch")
+	}
+
+	manager := &extensionManager{extensions: map[string]*loadedExtension{}}
+	downloadExt := newTestLoadedExtension(t, ExtensionTypeDownloadProvider, ExtensionTypeMetadataProvider)
+	manager.extensions[downloadExt.ID] = downloadExt
+	if providers := manager.GetDownloadProviders(); len(providers) != 1 {
+		t.Fatalf("download providers = %#v", providers)
+	}
+	SetProviderPriority([]string{"deezer", "coverage-ext", "coverage-ext", " "})
+	if priority := GetProviderPriority(); len(priority) != 1 || priority[0] != "coverage-ext" {
+		t.Fatalf("provider priority = %#v", priority)
+	}
+	SetExtensionFallbackProviderIDs([]string{"a", "a", " ", "b"})
+	if ids := GetExtensionFallbackProviderIDs(); len(ids) != 2 || !isExtensionFallbackAllowed("a") || isExtensionFallbackAllowed("z") {
+		t.Fatalf("fallback ids = %#v", ids)
+	}
+	SetExtensionFallbackProviderIDs(nil)
+	if !isExtensionFallbackAllowed("z") {
+		t.Fatal("nil fallback list should allow all")
+	}
+	SetMetadataProviderPriority([]string{"spotify", "deezer", "coverage-ext", "coverage-ext"})
+	if priority := GetMetadataProviderPriority(); len(priority) != 1 || priority[0] != "coverage-ext" {
+		t.Fatalf("metadata priority = %#v", priority)
+	}
+}
@@ -1,14 +1,88 @@
 package gobackend

-import "testing"
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+	"time"

-func TestSetMetadataProviderPriorityAddsBuiltIns(t *testing.T) {
+	"github.com/dop251/goja"
+)
+
+func TestSetMetadataProviderPriorityStripsRetiredBuiltIns(t *testing.T) {
 	original := GetMetadataProviderPriority()
 	defer SetMetadataProviderPriority(original)

-	SetMetadataProviderPriority([]string{"tidal"})
+	SetMetadataProviderPriority([]string{"qobuz"})
 	got := GetMetadataProviderPriority()
-	want := []string{"tidal", "deezer", "qobuz"}
+	if len(got) != 0 {
+		t.Fatalf("expected retired built-in qobuz to be stripped, got %v", got)
+	}
+}
+
+func TestSetExtensionFallbackProviderIDsDedupesExtensions(t *testing.T) {
+	original := GetExtensionFallbackProviderIDs()
+	defer SetExtensionFallbackProviderIDs(original)
+
+	SetExtensionFallbackProviderIDs([]string{"ext-a", "ext-a", " ext-b "})
+
+	got := GetExtensionFallbackProviderIDs()
+	want := []string{"ext-a", "ext-b"}
+	if len(got) != len(want) {
+		t.Fatalf("unexpected fallback provider length: got %v want %v", got, want)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("unexpected fallback provider at %d: got %v want %v", i, got, want)
+		}
+	}
+}
+
+func TestIsExtensionFallbackAllowedDefaultsToAllExtensions(t *testing.T) {
+	original := GetExtensionFallbackProviderIDs()
+	defer SetExtensionFallbackProviderIDs(original)
+
+	SetExtensionFallbackProviderIDs(nil)
+
+	if !isExtensionFallbackAllowed("custom-ext") {
+		t.Fatal("expected custom extension to be allowed when no fallback allowlist is configured")
+	}
+}
+
+func TestIsExtensionFallbackAllowedRespectsAllowlist(t *testing.T) {
+	original := GetExtensionFallbackProviderIDs()
+	defer SetExtensionFallbackProviderIDs(original)
+
+	SetExtensionFallbackProviderIDs([]string{"allowed-ext"})
+
+	if !isExtensionFallbackAllowed("allowed-ext") {
+		t.Fatal("expected explicitly allowed extension to be permitted")
+	}
+	if isExtensionFallbackAllowed("blocked-ext") {
+		t.Fatal("expected extension outside allowlist to be blocked")
+	}
+	if isExtensionFallbackAllowed("deezer") {
+		t.Fatal("expected retired Deezer downloader to respect extension fallback allowlist")
+	}
+}
+
+func TestSetProviderPriorityRemovesRetiredDeezerDownloader(t *testing.T) {
+	original := GetProviderPriority()
+	defer SetProviderPriority(original)
+
+	SetProviderPriority([]string{"deezer", "qobuz", "custom-ext"})
+
+	got := GetProviderPriority()
+	want := []string{"custom-ext"}
 	if len(got) != len(want) {
 		t.Fatalf("unexpected priority length: got %v want %v", got, want)
 	}
@@ -19,50 +93,696 @@ func TestSetMetadataProviderPriorityAddsBuiltIns(t *testing.T) {
 	}
 }

-func TestSearchTracksWithMetadataProvidersUsesPriorityAndDedupes(t *testing.T) {
-	originalPriority := GetMetadataProviderPriority()
-	originalSearch := searchBuiltInMetadataTracksFunc
+func TestSetProviderPriorityKeepsExtensionNamedLikeRetiredDownloader(t *testing.T) {
+	original := GetProviderPriority()
+	defer SetProviderPriority(original)
+
+	manager := getExtensionManager()
+	ext := newTestLoadedExtension(t, ExtensionTypeDownloadProvider)
+	ext.ID = "deezer"
+	ext.Manifest.Name = "deezer"
+
+	manager.mu.Lock()
+	previous, hadPrevious := manager.extensions[ext.ID]
+	manager.extensions[ext.ID] = ext
+	manager.mu.Unlock()
 	defer func() {
-		SetMetadataProviderPriority(originalPriority)
-		searchBuiltInMetadataTracksFunc = originalSearch
+		manager.mu.Lock()
+		if hadPrevious {
+			manager.extensions[ext.ID] = previous
+		} else {
+			delete(manager.extensions, ext.ID)
+		}
+		manager.mu.Unlock()
 	}()

-	SetMetadataProviderPriority([]string{"qobuz", "tidal", "deezer"})
+	SetProviderPriority([]string{"deezer", "custom-ext"})

-	var calls []string
-	searchBuiltInMetadataTracksFunc = func(providerID, query string, limit int) ([]ExtTrackMetadata, error) {
-		calls = append(calls, providerID)
-		switch providerID {
-		case "qobuz":
-			return []ExtTrackMetadata{
-				{ProviderID: "qobuz", SpotifyID: "qobuz:1", ISRC: "AAA111", Name: "First"},
-			}, nil
-		case "tidal":
-			return []ExtTrackMetadata{
-				{ProviderID: "tidal", SpotifyID: "tidal:2", ISRC: "AAA111", Name: "Duplicate"},
-				{ProviderID: "tidal", SpotifyID: "tidal:3", ISRC: "BBB222", Name: "Second"},
-			}, nil
-		case "deezer":
-			return []ExtTrackMetadata{
-				{ProviderID: "deezer", SpotifyID: "deezer:4", ISRC: "CCC333", Name: "Third"},
-			}, nil
-		default:
-			return nil, nil
+	got := GetProviderPriority()
+	want := []string{"deezer", "custom-ext"}
+	if len(got) != len(want) {
+		t.Fatalf("unexpected priority length: got %v want %v", got, want)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("unexpected priority at %d: got %v want %v", i, got, want)
+		}
+	}
+}
+
+func TestPrioritizeFallbackProvidersByHealthPrefersOnlineAndSkipsOffline(t *testing.T) {
+	manager := getExtensionManager()
+	amazon := newTestLoadedExtension(t, ExtensionTypeDownloadProvider)
+	amazon.ID = "amazon"
+	amazon.Manifest.Name = "amazon"
+	amazon.Manifest.ServiceHealth = []ExtensionHealthCheck{{
+		ID:       "main",
+		URL:      "://bad",
+		Required: true,
+	}}
+
+	plain := newTestLoadedExtension(t, ExtensionTypeDownloadProvider)
+	plain.ID = "plain"
+	plain.Manifest.Name = "plain"
+
+	deezer := newTestLoadedExtension(t, ExtensionTypeDownloadProvider)
+	deezer.ID = "deezer"
+	deezer.Manifest.Name = "deezer"
+	deezer.Manifest.ServiceHealth = []ExtensionHealthCheck{{
+		ID:  "main",
+		URL: "https://example.test/health",
+	}}
+
+	manager.mu.Lock()
+	previousAmazon, hadAmazon := manager.extensions[amazon.ID]
+	previousPlain, hadPlain := manager.extensions[plain.ID]
+	previousDeezer, hadDeezer := manager.extensions[deezer.ID]
+	manager.extensions[amazon.ID] = amazon
+	manager.extensions[plain.ID] = plain
+	manager.extensions[deezer.ID] = deezer
+	manager.mu.Unlock()
+	defer func() {
+		manager.mu.Lock()
+		if hadAmazon {
+			manager.extensions[amazon.ID] = previousAmazon
+		} else {
+			delete(manager.extensions, amazon.ID)
+		}
+		if hadPlain {
+			manager.extensions[plain.ID] = previousPlain
+		} else {
+			delete(manager.extensions, plain.ID)
+		}
+		if hadDeezer {
+			manager.extensions[deezer.ID] = previousDeezer
+		} else {
+			delete(manager.extensions, deezer.ID)
+		}
+		manager.mu.Unlock()
+
+		extensionHealthCacheMu.Lock()
+		delete(extensionHealthCache, deezer.ID)
+		extensionHealthCacheMu.Unlock()
+	}()
+
+	extensionHealthCacheMu.Lock()
+	extensionHealthCache[deezer.ID] = cachedExtensionHealthResult{
+		result: ExtensionHealthResult{
+			ExtensionID: deezer.ID,
+			Status:      "online",
+			CheckedAt:   time.Now().UTC().Format(time.RFC3339),
+		},
+		expiresAt: time.Now().Add(time.Minute),
+	}
+	extensionHealthCacheMu.Unlock()
+
+	got := prioritizeFallbackProvidersByHealth(
+		[]string{"amazon", "plain", "deezer"},
+		manager,
+		"",
+	)
+	want := []string{"deezer", "plain"}
+	if len(got) != len(want) {
+		t.Fatalf("unexpected provider order length: got %v want %v", got, want)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("unexpected provider order at %d: got %v want %v", i, got, want)
+		}
+	}
+}
+
+func TestNormalizeDownloadDecryptionInfoPromotesLegacyKey(t *testing.T) {
+	normalized := normalizeDownloadDecryptionInfo(nil, " 001122 ")
+	if normalized == nil {
+		t.Fatal("expected legacy decryption key to produce normalized descriptor")
+	}
+	if normalized.Strategy != genericFFmpegMOVDecryptionStrategy {
+		t.Fatalf("strategy = %q", normalized.Strategy)
+	}
+	if normalized.Key != "001122" {
+		t.Fatalf("key = %q", normalized.Key)
+	}
+	if normalized.InputFormat != "mov" {
+		t.Fatalf("input format = %q", normalized.InputFormat)
+	}
+}
+
+func TestNormalizeDownloadDecryptionInfoCanonicalizesMovAliases(t *testing.T) {
+	normalized := normalizeDownloadDecryptionInfo(&DownloadDecryptionInfo{
+		Strategy:    "mp4_decryption_key",
+		Key:         "abcd",
+		InputFormat: "",
+	}, "")
+	if normalized == nil {
+		t.Fatal("expected descriptor to remain available")
+	}
+	if normalized.Strategy != genericFFmpegMOVDecryptionStrategy {
+		t.Fatalf("strategy = %q", normalized.Strategy)
+	}
+	if normalized.InputFormat != "mov" {
+		t.Fatalf("input format = %q", normalized.InputFormat)
+	}
+}
+
+func TestExtensionDownloadUsesIsolatedRuntimeForConcurrentCalls(t *testing.T) {
+	server := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		time.Sleep(500 * time.Millisecond)
+		_, _ = w.Write([]byte("ok"))
+	}))
+	defer server.Close()
+	setPrivateIPCache("download.test", false, time.Minute)
+
+	originalTransport := sharedTransport
+	testTransport := &http.Transport{
+		DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+			return (&net.Dialer{}).DialContext(ctx, network, server.Listener.Addr().String())
+		},
+		TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
+	}
+	sharedTransport = testTransport
+	defer func() {
+		testTransport.CloseIdleConnections()
+		sharedTransport = originalTransport
+	}()
+
+	extDir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(extDir, "index.js"), []byte(`
+		registerExtension({
+			download: function(trackID, quality, outputPath, onProgress) {
+				var result = file.download('https://download.test/' + trackID, outputPath, {
+					onProgress: function(written, total) {
+						if (onProgress) onProgress(50);
+					}
+				});
+				if (!result || !result.success) {
+					return {
+						success: false,
+						error_message: result && result.error ? result.error : 'download failed',
+						error_type: 'download_error'
+					};
+				}
+				if (onProgress) onProgress(100);
+				return { success: true, file_path: result.path };
+			}
+		});
+	`), 0600); err != nil {
+		t.Fatalf("write extension index: %v", err)
+	}
+
+	outputDir := t.TempDir()
+	SetAllowedDownloadDirs([]string{outputDir})
+	defer SetAllowedDownloadDirs(nil)
+
+	ext := &loadedExtension{
+		ID: "concurrent-download",
+		Manifest: &ExtensionManifest{
+			Name:        "concurrent-download",
+			Description: "Concurrent download test",
+			Version:     "1.0.0",
+			Types:       []ExtensionType{ExtensionTypeDownloadProvider},
+			Permissions: ExtensionPermissions{
+				Network: []string{"download.test"},
+				File:    true,
+			},
+		},
+		Enabled:   true,
+		SourceDir: extDir,
+		DataDir:   t.TempDir(),
+	}
+	provider := newExtensionProviderWrapper(ext)
+
+	start := time.Now()
+	var wg sync.WaitGroup
+	errs := make(chan error, 2)
+	for i := 0; i < 2; i++ {
+		i := i
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			result, err := provider.Download(
+				fmt.Sprintf("track-%d", i),
+				"LOSSLESS",
+				filepath.Join(outputDir, fmt.Sprintf("track-%d.flac", i)),
+				"",
+				nil,
+			)
+			if err != nil {
+				errs <- err
+				return
+			}
+			if result == nil || !result.Success {
+				errs <- fmt.Errorf("download failed: %#v", result)
+			}
+		}()
+	}
+	wg.Wait()
+	close(errs)
+	for err := range errs {
+		if err != nil {
+			t.Fatal(err)
 		}
 	}

-	manager := GetExtensionManager()
+	if elapsed := time.Since(start); elapsed >= 850*time.Millisecond {
+		t.Fatalf("expected same-extension downloads to overlap, elapsed %s", elapsed)
+	}
+}
+
+func TestBuildOutputPathAddsExplicitOutputDirToAllowedDirs(t *testing.T) {
+	SetAllowedDownloadDirs(nil)
+
+	outputDir := t.TempDir()
+	outputPath := buildOutputPath(DownloadRequest{
+		TrackName:      "Song",
+		ArtistName:     "Artist",
+		OutputDir:      outputDir,
+		OutputExt:      ".flac",
+		FilenameFormat: "",
+	})
+
+	if !isPathInAllowedDirs(outputPath) {
+		t.Fatalf("expected output path %q to be allowed", outputPath)
+	}
+}
+
+func TestBuildOutputPathForExtensionAddsExplicitOutputPathDirToAllowedDirs(t *testing.T) {
+	SetAllowedDownloadDirs(nil)
+
+	outputDir := t.TempDir()
+	outputPath := filepath.Join(outputDir, "custom.flac")
+	ext := &loadedExtension{DataDir: t.TempDir()}
+
+	resolved := buildOutputPathForExtension(DownloadRequest{
+		OutputPath: outputPath,
+	}, ext)
+
+	if resolved != outputPath {
+		t.Fatalf("resolved output path = %q", resolved)
+	}
+	if !isPathInAllowedDirs(outputPath) {
+		t.Fatalf("expected output path %q to be allowed", outputPath)
+	}
+}
+
+func TestBuildOutputPathForExtensionUsesTempDirForFDOutput(t *testing.T) {
+	SetAllowedDownloadDirs(nil)
+
+	ext := &loadedExtension{DataDir: t.TempDir()}
+	resolved := buildOutputPathForExtension(DownloadRequest{
+		TrackName:  "Song",
+		ArtistName: "Artist",
+		OutputDir:  filepath.Join("Artist", "Album"),
+		OutputFD:   123,
+		OutputExt:  ".flac",
+	}, ext)
+
+	expectedBase := filepath.Join(ext.DataDir, "downloads")
+	if !isPathWithinBase(expectedBase, resolved) {
+		t.Fatalf("expected SAF extension output under %q, got %q", expectedBase, resolved)
+	}
+	if !isPathInAllowedDirs(resolved) {
+		t.Fatalf("expected resolved output path %q to be allowed", resolved)
+	}
+}
+
+func TestBuildOutputPathSanitizesTemplateFilename(t *testing.T) {
+	SetAllowedDownloadDirs(nil)
+
+	outputDir := t.TempDir()
+	outputPath := buildOutputPath(DownloadRequest{
+		TrackName:      `Gehra Hua (From "Dhurandhar")`,
+		ArtistName:     "Artist",
+		OutputDir:      outputDir,
+		OutputExt:      ".flac",
+		FilenameFormat: "{artist} - {title}",
+	})
+
+	base := filepath.Base(outputPath)
+	if strings.ContainsAny(base, `<>:"/\|?*`) {
+		t.Fatalf("output filename still contains illegal characters: %q", base)
+	}
+	if strings.Contains(base, `"`) {
+		t.Fatalf("output filename still contains straight double quote: %q", base)
+	}
+}
+
+func TestBuildOutputPathForExtensionSanitizesTemplateFilename(t *testing.T) {
+	SetAllowedDownloadDirs(nil)
+
+	ext := &loadedExtension{DataDir: t.TempDir()}
+	resolved := buildOutputPathForExtension(DownloadRequest{
+		TrackName:      `Gehra Hua (From "Dhurandhar")`,
+		ArtistName:     "Artist",
+		OutputFD:       123,
+		OutputExt:      ".flac",
+		FilenameFormat: "{artist} - {title}",
+	}, ext)
+
+	base := filepath.Base(resolved)
+	if strings.ContainsAny(base, `<>:"/\|?*`) {
+		t.Fatalf("extension output filename still contains illegal characters: %q", base)
+	}
+}
+
+func TestShouldStopProviderFallback(t *testing.T) {
+	if shouldStopProviderFallback(nil) {
+		t.Fatal("nil availability should not stop fallback")
+	}
+	if shouldStopProviderFallback(&ExtAvailabilityResult{Available: false}) {
+		t.Fatal("availability without skip_fallback should not stop fallback")
+	}
+	if !shouldStopProviderFallback(&ExtAvailabilityResult{Available: false, SkipFallback: true}) {
+		t.Fatal("skip_fallback availability should stop fallback")
+	}
+}
+
+func TestBuildExtensionFallbackStoppedResponsePrefersAvailabilityReason(t *testing.T) {
+	resp := buildExtensionFallbackStoppedResponse("soundcloud", &ExtAvailabilityResult{
+		Reason:       "direct SoundCloud track ID",
+		SkipFallback: true,
+	}, errors.New("ignored"))
+
+	if resp.Service != "soundcloud" {
+		t.Fatalf("service = %q", resp.Service)
+	}
+	if resp.Error != "Fallback stopped by soundcloud: direct SoundCloud track ID" {
+		t.Fatalf("unexpected error message: %q", resp.Error)
+	}
+	if resp.ErrorType != "extension_error" {
+		t.Fatalf("error type = %q", resp.ErrorType)
+	}
+}
+
+func TestBuildExtensionFallbackStoppedResponseFallsBackToError(t *testing.T) {
+	resp := buildExtensionFallbackStoppedResponse("soundcloud", &ExtAvailabilityResult{
+		SkipFallback: true,
+	}, errors.New("lookup failed"))
+
+	if resp.Error != "Fallback stopped by soundcloud: lookup failed" {
+		t.Fatalf("unexpected error message: %q", resp.Error)
+	}
+}
+
+func TestShouldAbortCancelledFallbackWithCancelledError(t *testing.T) {
+	if !shouldAbortCancelledFallback("", ErrDownloadCancelled) {
+		t.Fatal("expected cancelled error to abort fallback")
+	}
+}
+
+func TestShouldAbortCancelledFallbackWithCancelledItemState(t *testing.T) {
+	const itemID = "cancelled-item"
+	initDownloadCancel(itemID)
+	defer clearDownloadCancel(itemID)
+
+	cancelDownload(itemID)
+
+	if !shouldAbortCancelledFallback(itemID, errors.New("generic failure")) {
+		t.Fatal("expected cancelled item state to abort fallback even for generic errors")
+	}
+}
+
+func TestCanEmbedGenreLabelRequiresExistingAbsoluteLocalFile(t *testing.T) {
+	tempFile := filepath.Join(t.TempDir(), "track.flac")
+	if err := os.WriteFile(tempFile, []byte("fLaC"), 0644); err != nil {
+		t.Fatalf("failed to create temp file: %v", err)
+	}
+	tempM4A := filepath.Join(t.TempDir(), "track.m4a")
+	if err := os.WriteFile(tempM4A, []byte("not-flac"), 0644); err != nil {
+		t.Fatalf("failed to create temp m4a file: %v", err)
+	}
+
+	if canEmbedGenreLabel("relative.flac") {
+		t.Fatal("expected relative path to be rejected")
+	}
+	if canEmbedGenreLabel("content://example") {
+		t.Fatal("expected content URI to be rejected")
+	}
+	if canEmbedGenreLabel(filepath.Join(t.TempDir(), "missing.flac")) {
+		t.Fatal("expected missing file to be rejected")
+	}
+	if canEmbedGenreLabel(tempM4A) {
+		t.Fatalf("expected non-FLAC file %q to be rejected", tempM4A)
+	}
+	if !canEmbedGenreLabel(tempFile) {
+		t.Fatalf("expected existing absolute file %q to be accepted", tempFile)
+	}
+}
+
+func TestSearchTracksWithMetadataProvidersIgnoresRetiredBuiltIns(t *testing.T) {
+	originalPriority := GetMetadataProviderPriority()
+	defer func() {
+		SetMetadataProviderPriority(originalPriority)
+	}()
+
+	SetMetadataProviderPriority([]string{"qobuz"})
+
+	manager := getExtensionManager()
 	tracks, err := manager.SearchTracksWithMetadataProviders("query", 3, false)
 	if err != nil {
 		t.Fatalf("SearchTracksWithMetadataProviders returned error: %v", err)
 	}
-	if len(tracks) != 3 {
-		t.Fatalf("unexpected track count: got %d want 3", len(tracks))
-	}
-	if tracks[0].ProviderID != "qobuz" || tracks[1].ProviderID != "tidal" || tracks[2].ProviderID != "deezer" {
-		t.Fatalf("unexpected track provider order: %+v", tracks)
-	}
-	if len(calls) != 3 || calls[0] != "qobuz" || calls[1] != "tidal" || calls[2] != "deezer" {
-		t.Fatalf("unexpected provider call order: %v", calls)
+	if len(tracks) != 0 {
+		t.Fatalf("expected no tracks from retired built-in provider, got %+v", tracks)
+	}
+}
+
+func TestParseExtensionSearchResultAcceptsObjectAndArrayShapes(t *testing.T) {
+	vm := goja.New()
+	value, err := vm.RunString(`({
+		tracks: [{
+			id: "track-1",
+			name: "Song",
+			artists: "Artist",
+			album_name: "Album",
+			duration_ms: 123000,
+			cover_url: "https://img.test/cover.jpg",
+			external_links: { spotify: "spotify:track:1" },
+			audio_quality: "LOSSLESS"
+		}],
+		total: 9
+	})`)
+	if err != nil {
+		t.Fatalf("build object search result: %v", err)
+	}
+
+	result, err := parseExtensionSearchResult(vm, value)
+	if err != nil {
+		t.Fatalf("parse object search result: %v", err)
+	}
+	if result.Total != 9 || len(result.Tracks) != 1 {
+		t.Fatalf("unexpected object result: %+v", result)
+	}
+	track := result.Tracks[0]
+	if track.ID != "track-1" ||
+		track.AlbumName != "Album" ||
+		track.DurationMS != 123000 ||
+		track.CoverURL != "https://img.test/cover.jpg" ||
+		track.ExternalLinks["spotify"] != "spotify:track:1" ||
+		track.AudioQuality != "LOSSLESS" {
+		t.Fatalf("unexpected parsed track: %+v", track)
+	}
+
+	arrayValue, err := vm.RunString(`[
+		{id: "track-2", name: "Other Song", artists: "Other Artist", albumName: "Other Album", durationMs: 456000}
+	]`)
+	if err != nil {
+		t.Fatalf("build array search result: %v", err)
+	}
+
+	arrayResult, err := parseExtensionSearchResult(vm, arrayValue)
+	if err != nil {
+		t.Fatalf("parse array search result: %v", err)
+	}
+	if arrayResult.Total != 1 ||
+		len(arrayResult.Tracks) != 1 ||
+		arrayResult.Tracks[0].AlbumName != "Other Album" ||
+		arrayResult.Tracks[0].DurationMS != 456000 {
+		t.Fatalf("unexpected array result: %+v", arrayResult)
+	}
+}
+
+func TestParseExtensionMetadataAndDownloadResults(t *testing.T) {
+	vm := goja.New()
+	value, err := vm.RunString(`({
+		id: "album-1",
+		name: "Album",
+		artists: "Artist",
+		artistId: "artist-1",
+		coverUrl: "https://img.test/album.jpg",
+		releaseDate: "2024-02-03",
+		totalTracks: 2,
+		albumType: "album",
+		tracks: [
+			{id: "track-1", name: "Song 1", artists: "Artist", durationMs: 180000},
+			{id: "track-2", name: "Song 2", artists: "Artist", duration_ms: 181000}
+		]
+	})`)
+	if err != nil {
+		t.Fatalf("build album value: %v", err)
+	}
+
+	album, err := parseExtensionAlbumValue(vm, value)
+	if err != nil {
+		t.Fatalf("parse album: %v", err)
+	}
+	if album.ID != "album-1" ||
+		album.ArtistID != "artist-1" ||
+		album.CoverURL != "https://img.test/album.jpg" ||
+		album.TotalTracks != 2 ||
+		len(album.Tracks) != 2 ||
+		album.Tracks[0].DurationMS != 180000 ||
+		album.Tracks[1].DurationMS != 181000 {
+		t.Fatalf("unexpected album: %+v", album)
+	}
+
+	artistValue, err := vm.RunString(`({
+		id: "artist-1",
+		name: "Artist",
+		imageUrl: "https://img.test/artist.jpg",
+		headerImage: "https://img.test/header.jpg",
+		listeners: 1234,
+		albums: [{id: "album-1", name: "Album", tracks: [{id: "track-1", name: "Song"}]}],
+		releases: [{id: "single-1", name: "Single"}],
+		topTracks: [{id: "top-1", name: "Top Song"}]
+	})`)
+	if err != nil {
+		t.Fatalf("build artist value: %v", err)
+	}
+
+	artist, err := parseExtensionArtistValue(vm, artistValue)
+	if err != nil {
+		t.Fatalf("parse artist: %v", err)
+	}
+	if artist.ID != "artist-1" ||
+		artist.ImageURL != "https://img.test/artist.jpg" ||
+		artist.HeaderImage != "https://img.test/header.jpg" ||
+		artist.Listeners != 1234 ||
+		len(artist.Albums) != 1 ||
+		len(artist.Albums[0].Tracks) != 1 ||
+		len(artist.Releases) != 1 ||
+		len(artist.TopTracks) != 1 {
+		t.Fatalf("unexpected artist: %+v", artist)
+	}
+
+	downloadValue, err := vm.RunString(`({
+		success: true,
+		filePath: "/tmp/song.flac",
+		alreadyExists: true,
+		bitDepth: 24,
+		sampleRate: 96000,
+		title: "Song",
+		albumArtist: "Album Artist",
+		lyricsLrc: "[00:00.00]Line",
+		decryptionKey: "001122",
+		decryption: {
+			strategy: "mp4_decryption_key",
+			key: "001122",
+			inputFormat: "m4a",
+			options: { map: "0:a" }
+		}
+	})`)
+	if err != nil {
+		t.Fatalf("build download value: %v", err)
+	}
+
+	download := parseExtensionDownloadResultValue(vm, downloadValue)
+	if !download.Success ||
+		download.FilePath != "/tmp/song.flac" ||
+		!download.AlreadyExists ||
+		download.BitDepth != 24 ||
+		download.SampleRate != 96000 ||
+		download.AlbumArtist != "Album Artist" ||
+		download.LyricsLRC != "[00:00.00]Line" ||
+		download.Decryption == nil ||
+		download.Decryption.InputFormat != "m4a" ||
+		download.Decryption.Options["map"] != "0:a" {
+		t.Fatalf("unexpected download result: %+v", download)
+	}
+
+	availabilityValue, err := vm.RunString(`({ available: true, trackId: "track-1", skipFallback: true, reason: "direct" })`)
+	if err != nil {
+		t.Fatalf("build availability value: %v", err)
+	}
+	availability := parseExtensionAvailabilityValue(vm, availabilityValue)
+	if !availability.Available || availability.TrackID != "track-1" || !availability.SkipFallback || availability.Reason != "direct" {
+		t.Fatalf("unexpected availability: %+v", availability)
+	}
+}
+
+func TestParseExtensionURLHandleResult(t *testing.T) {
+	vm := goja.New()
+	value, err := vm.RunString(`({
+		type: "album",
+		name: "Shared Album",
+		coverUrl: "https://img.test/shared.jpg",
+		track: { id: "track-1", name: "Song" },
+		tracks: [{ id: "track-2", name: "Song 2" }],
+		album: { id: "album-1", name: "Album", tracks: [{ id: "track-3", name: "Song 3" }] },
+		artist: { id: "artist-1", name: "Artist", topTracks: [{ id: "track-4", name: "Song 4" }] }
+	})`)
+	if err != nil {
+		t.Fatalf("build URL handle value: %v", err)
+	}
+
+	result, err := parseExtensionURLHandleValue(vm, value)
+	if err != nil {
+		t.Fatalf("parse URL handle: %v", err)
+	}
+	if result.Type != "album" ||
+		result.CoverURL != "https://img.test/shared.jpg" ||
+		result.Track == nil ||
+		result.Track.ID != "track-1" ||
+		len(result.Tracks) != 1 ||
+		result.Album == nil ||
+		len(result.Album.Tracks) != 1 ||
+		result.Artist == nil ||
+		len(result.Artist.TopTracks) != 1 {
+		t.Fatalf("unexpected URL handle result: %+v", result)
+	}
+}
+
+func TestParseExtensionAuxiliaryResults(t *testing.T) {
+	vm := goja.New()
+
+	matchValue, err := vm.RunString(`({ matched: true, trackId: "track-1", confidence: 0.92, reason: "isrc" })`)
+	if err != nil {
+		t.Fatalf("build match value: %v", err)
+	}
+	match := parseExtensionMatchTrackValue(vm, matchValue)
+	if !match.Matched || match.TrackID != "track-1" || match.Confidence != 0.92 || match.Reason != "isrc" {
+		t.Fatalf("unexpected match result: %+v", match)
+	}
+
+	postValue, err := vm.RunString(`({ success: true, newFilePath: "/tmp/new.flac", newFileUri: "content://new", bitDepth: 24, sampleRate: 96000 })`)
+	if err != nil {
+		t.Fatalf("build post-process value: %v", err)
+	}
+	post := parseExtensionPostProcessValue(vm, postValue)
+	if !post.Success || post.NewFilePath != "/tmp/new.flac" || post.NewFileURI != "content://new" || post.BitDepth != 24 || post.SampleRate != 96000 {
+		t.Fatalf("unexpected post-process result: %+v", post)
+	}
+
+	lyricsValue, err := vm.RunString(`({
+		syncType: "LINE_SYNCED",
+		instrumental: false,
+		plainLyrics: "Line",
+		provider: "Lyrics Provider",
+		lines: [{ startTimeMs: 1000, words: "Line", endTimeMs: 2000 }]
+	})`)
+	if err != nil {
+		t.Fatalf("build lyrics value: %v", err)
+	}
+	lyrics, err := parseExtensionLyricsValue(vm, lyricsValue)
+	if err != nil {
+		t.Fatalf("parse lyrics: %v", err)
+	}
+	if lyrics.SyncType != "LINE_SYNCED" ||
+		lyrics.PlainLyrics != "Line" ||
+		lyrics.Provider != "Lyrics Provider" ||
+		len(lyrics.Lines) != 1 ||
+		lyrics.Lines[0].StartTimeMs != 1000 ||
+		lyrics.Lines[0].EndTimeMs != 2000 {
+		t.Fatalf("unexpected lyrics result: %+v", lyrics)
 	}
 }
@@ -5,6 +5,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -80,7 +81,7 @@ func SetExtensionTokens(extensionID string, accessToken, refreshToken string, ex
 	state.IsAuthenticated = accessToken != ""
 }

-type ExtensionRuntime struct {
+type extensionRuntime struct {
 	extensionID    string
 	manifest       *ExtensionManifest
 	settings       map[string]interface{}
@@ -90,6 +91,12 @@ type ExtensionRuntime struct {
 	dataDir        string
 	vm             *goja.Runtime

+	activeDownloadMu     sync.RWMutex
+	activeDownloadItemID string
+
+	activeRequestMu sync.RWMutex
+	activeRequestID string
+
 	storageMu      sync.RWMutex
 	storageCache   map[string]interface{}
 	storageLoaded  bool
@@ -120,10 +127,10 @@ var (
 	privateIPCacheMu sync.RWMutex
 )

-func NewExtensionRuntime(ext *LoadedExtension) *ExtensionRuntime {
+func newExtensionRuntime(ext *loadedExtension) *extensionRuntime {
 	jar, _ := newSimpleCookieJar()

-	runtime := &ExtensionRuntime{
+	runtime := &extensionRuntime{
 		extensionID:       ext.ID,
 		manifest:          ext.Manifest,
 		settings:          make(map[string]interface{}),
@@ -133,24 +140,131 @@ func NewExtensionRuntime(ext *LoadedExtension) *ExtensionRuntime {
 		storageFlushDelay: defaultStorageFlushDelay,
 	}

-	runtime.httpClient = newExtensionHTTPClient(ext, jar, 30*time.Second)
-	runtime.downloadClient = newExtensionHTTPClient(ext, jar, DownloadTimeout)
+	runtime.httpClient = newExtensionHTTPClient(ext, jar, extensionHTTPTimeout(ext, 30*time.Second), true)
+	runtime.downloadClient = newExtensionHTTPClient(ext, jar, DownloadTimeout, false)

 	return runtime
 }

-func newExtensionHTTPClient(ext *LoadedExtension, jar http.CookieJar, timeout time.Duration) *http.Client {
+func extensionHTTPTimeout(ext *loadedExtension, fallback time.Duration) time.Duration {
+	if ext == nil || ext.Manifest == nil || ext.Manifest.Capabilities == nil {
+		return fallback
+	}
+
+	raw, ok := ext.Manifest.Capabilities["networkTimeoutSeconds"]
+	if !ok {
+		return fallback
+	}
+
+	seconds := parseExtensionTimeoutSeconds(raw)
+	if seconds <= 0 {
+		return fallback
+	}
+
+	if seconds < 5 {
+		seconds = 5
+	}
+	if seconds > 300 {
+		seconds = 300
+	}
+
+	return time.Duration(seconds) * time.Second
+}
+
+func parseExtensionTimeoutSeconds(raw interface{}) int {
+	switch v := raw.(type) {
+	case int:
+		return v
+	case int32:
+		return int(v)
+	case int64:
+		return int(v)
+	case float32:
+		return int(v)
+	case float64:
+		return int(v)
+	case string:
+		parsed, err := strconv.Atoi(strings.TrimSpace(v))
+		if err != nil {
+			return 0
+		}
+		return parsed
+	default:
+		return 0
+	}
+}
+
+func (r *extensionRuntime) setActiveDownloadItemID(itemID string) {
+	r.activeDownloadMu.Lock()
+	defer r.activeDownloadMu.Unlock()
+	r.activeDownloadItemID = strings.TrimSpace(itemID)
+}
+
+func (r *extensionRuntime) clearActiveDownloadItemID() {
+	r.activeDownloadMu.Lock()
+	defer r.activeDownloadMu.Unlock()
+	r.activeDownloadItemID = ""
+}
+
+func (r *extensionRuntime) getActiveDownloadItemID() string {
+	r.activeDownloadMu.RLock()
+	defer r.activeDownloadMu.RUnlock()
+	return r.activeDownloadItemID
+}
+
+func (r *extensionRuntime) setActiveRequestID(requestID string) {
+	r.activeRequestMu.Lock()
+	defer r.activeRequestMu.Unlock()
+	r.activeRequestID = strings.TrimSpace(requestID)
+}
+
+func (r *extensionRuntime) clearActiveRequestID() {
+	r.activeRequestMu.Lock()
+	defer r.activeRequestMu.Unlock()
+	r.activeRequestID = ""
+}
+
+func (r *extensionRuntime) getActiveRequestID() string {
+	r.activeRequestMu.RLock()
+	defer r.activeRequestMu.RUnlock()
+	return r.activeRequestID
+}
+
+func (r *extensionRuntime) bindDownloadCancelContext(req *http.Request) *http.Request {
+	if req == nil {
+		return nil
+	}
+
+	itemID := r.getActiveDownloadItemID()
+	if itemID == "" {
+		requestID := r.getActiveRequestID()
+		if requestID == "" {
+			return req
+		}
+		return req.WithContext(initExtensionRequestCancel(requestID))
+	}
+
+	return req.WithContext(initDownloadCancel(itemID))
+}
+
+func newExtensionHTTPClient(ext *loadedExtension, jar http.CookieJar, timeout time.Duration, compressResponses bool) *http.Client {
 	// Extension sandbox enforces HTTPS-only domains. Do not apply global
 	// allow_http scheme downgrade here, because some extension APIs (e.g.
 	// spotify-web) will redirect http -> https and can end up in 301 loops.
-	// We still reuse sharedTransport so insecure TLS compatibility mode remains effective.
+	// API calls can use response compression for faster metadata/search loads,
+	// while media downloads keep identity transfer semantics for progress/streaming.
+	transport := sharedTransport
+	if compressResponses {
+		transport = extensionAPITransport
+	}
 	client := &http.Client{
-		Transport: sharedTransport,
+		Transport: transport,
 		Timeout:   timeout,
 		Jar:       jar,
 	}
 	client.CheckRedirect = func(req *http.Request, via []*http.Request) error {
-		if req.URL.Scheme != "https" {
+		if req.URL.Scheme != "https" &&
+			!(req.URL.Scheme == "http" && ext.Manifest.Permissions.AllowHTTP) {
 			GoLog("[Extension:%s] Redirect blocked: non-https scheme '%s'\n", ext.ID, req.URL.Scheme)
 			return fmt.Errorf("redirect blocked: only https is allowed")
 		}
@@ -308,11 +422,11 @@ func (j *simpleCookieJar) Cookies(u *url.URL) []*http.Cookie {
 	return j.cookies[u.Host]
 }

-func (r *ExtensionRuntime) SetSettings(settings map[string]interface{}) {
+func (r *extensionRuntime) SetSettings(settings map[string]interface{}) {
 	r.settings = settings
 }

-func (r *ExtensionRuntime) RegisterAPIs(vm *goja.Runtime) {
+func (r *extensionRuntime) RegisterAPIs(vm *goja.Runtime) {
 	r.vm = vm

 	httpObj := vm.NewObject()
@@ -356,7 +470,9 @@ func (r *ExtensionRuntime) RegisterAPIs(vm *goja.Runtime) {
 	fileObj.Set("exists", r.fileExists)
 	fileObj.Set("delete", r.fileDelete)
 	fileObj.Set("read", r.fileRead)
+	fileObj.Set("readBytes", r.fileReadBytes)
 	fileObj.Set("write", r.fileWrite)
+	fileObj.Set("writeBytes", r.fileWriteBytes)
 	fileObj.Set("copy", r.fileCopy)
 	fileObj.Set("move", r.fileMove)
 	fileObj.Set("getSize", r.fileGetSize)
@@ -386,8 +502,17 @@ func (r *ExtensionRuntime) RegisterAPIs(vm *goja.Runtime) {
 	utilsObj.Set("stringifyJSON", r.stringifyJSON)
 	utilsObj.Set("encrypt", r.cryptoEncrypt)
 	utilsObj.Set("decrypt", r.cryptoDecrypt)
+	utilsObj.Set("encryptBlockCipher", r.encryptBlockCipher)
+	utilsObj.Set("decryptBlockCipher", r.decryptBlockCipher)
+	utilsObj.Set("decryptCTRSegments", r.decryptCTRSegments)
 	utilsObj.Set("generateKey", r.cryptoGenerateKey)
 	utilsObj.Set("randomUserAgent", r.randomUserAgent)
+	utilsObj.Set("appVersion", r.appVersion)
+	utilsObj.Set("appUserAgent", r.appUserAgent)
+	utilsObj.Set("sleep", r.sleep)
+	utilsObj.Set("isDownloadCancelled", r.isDownloadCancelled)
+	utilsObj.Set("isRequestCancelled", r.isRequestCancelled)
+	utilsObj.Set("setDownloadStatus", r.setDownloadStatus)
 	vm.Set("utils", utilsObj)

 	logObj := vm.NewObject()
@@ -52,7 +52,7 @@ func summarizeURLForLog(urlStr string) string {
 	return fmt.Sprintf("%s://%s%s", parsed.Scheme, parsed.Host, parsed.Path)
 }

-func (r *ExtensionRuntime) authOpenUrl(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authOpenUrl(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -99,7 +99,7 @@ func (r *ExtensionRuntime) authOpenUrl(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) authGetCode(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authGetCode(call goja.FunctionCall) goja.Value {
 	extensionAuthStateMu.RLock()
 	defer extensionAuthStateMu.RUnlock()

@@ -111,7 +111,7 @@ func (r *ExtensionRuntime) authGetCode(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(state.AuthCode)
 }

-func (r *ExtensionRuntime) authSetCode(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authSetCode(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(false)
 	}
@@ -149,7 +149,7 @@ func (r *ExtensionRuntime) authSetCode(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(true)
 }

-func (r *ExtensionRuntime) authClear(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authClear(call goja.FunctionCall) goja.Value {
 	extensionAuthStateMu.Lock()
 	delete(extensionAuthState, r.extensionID)
 	extensionAuthStateMu.Unlock()
@@ -162,7 +162,7 @@ func (r *ExtensionRuntime) authClear(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(true)
 }

-func (r *ExtensionRuntime) authIsAuthenticated(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authIsAuthenticated(call goja.FunctionCall) goja.Value {
 	extensionAuthStateMu.RLock()
 	defer extensionAuthStateMu.RUnlock()

@@ -178,7 +178,7 @@ func (r *ExtensionRuntime) authIsAuthenticated(call goja.FunctionCall) goja.Valu
 	return r.vm.ToValue(state.IsAuthenticated)
 }

-func (r *ExtensionRuntime) authGetTokens(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authGetTokens(call goja.FunctionCall) goja.Value {
 	extensionAuthStateMu.RLock()
 	defer extensionAuthStateMu.RUnlock()

@@ -201,7 +201,6 @@ func (r *ExtensionRuntime) authGetTokens(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(result)
 }

-// Length should be between 43-128 characters (RFC 7636)
 func generatePKCEVerifier(length int) (string, error) {
 	if length < 43 {
 		length = 43
@@ -226,11 +225,10 @@ func generatePKCEVerifier(length int) (string, error) {

 func generatePKCEChallenge(verifier string) string {
 	hash := sha256.Sum256([]byte(verifier))
-	// Base64url encode without padding (RFC 7636)
 	return base64.RawURLEncoding.EncodeToString(hash[:])
 }

-func (r *ExtensionRuntime) authGeneratePKCE(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authGeneratePKCE(call goja.FunctionCall) goja.Value {
 	length := 64
 	if len(call.Arguments) > 0 && !goja.IsUndefined(call.Arguments[0]) {
 		if l, ok := call.Arguments[0].Export().(float64); ok && l >= 43 && l <= 128 {
@@ -267,7 +265,7 @@ func (r *ExtensionRuntime) authGeneratePKCE(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) authGetPKCE(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authGetPKCE(call goja.FunctionCall) goja.Value {
 	extensionAuthStateMu.RLock()
 	defer extensionAuthStateMu.RUnlock()

@@ -283,8 +281,7 @@ func (r *ExtensionRuntime) authGetPKCE(call goja.FunctionCall) goja.Value {
 	})
 }

-// config: { authUrl, clientId, redirectUri, scope, extraParams }
-func (r *ExtensionRuntime) authStartOAuthWithPKCE(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authStartOAuthWithPKCE(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -388,8 +385,7 @@ func (r *ExtensionRuntime) authStartOAuthWithPKCE(call goja.FunctionCall) goja.V
 	})
 }

-// config: { tokenUrl, clientId, redirectUri, code, extraParams }
-func (r *ExtensionRuntime) authExchangeCodeWithPKCE(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) authExchangeCodeWithPKCE(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -462,9 +458,10 @@ func (r *ExtensionRuntime) authExchangeCodeWithPKCE(call goja.FunctionCall) goja
 			"error":   err.Error(),
 		})
 	}
+	req = r.bindDownloadCancelContext(req)

 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
-	req.Header.Set("User-Agent", "SpotiFLAC-Extension/1.0")
+	req.Header.Set("User-Agent", appUserAgent())

 	resp, err := r.httpClient.Do(req)
 	if err != nil {
@@ -0,0 +1,535 @@
+package gobackend
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"encoding/base64"
+	"encoding/hex"
+	"fmt"
+	"strings"
+
+	"github.com/dop251/goja"
+	//lint:ignore SA1019 Blowfish is required for legacy extension crypto compatibility.
+	"golang.org/x/crypto/blowfish"
+)
+
+type runtimeBlockCipherOptions struct {
+	Algorithm      string
+	Mode           string
+	Key            []byte
+	IV             []byte
+	InputEncoding  string
+	OutputEncoding string
+	Padding        string
+}
+
+func parseRuntimeOptionsArgument(call goja.FunctionCall, index int) map[string]interface{} {
+	if len(call.Arguments) <= index {
+		return nil
+	}
+
+	value := call.Arguments[index]
+	if goja.IsUndefined(value) || goja.IsNull(value) {
+		return nil
+	}
+
+	exported := value.Export()
+	if options, ok := exported.(map[string]interface{}); ok {
+		return options
+	}
+	return nil
+}
+
+func runtimeOptionString(options map[string]interface{}, key, defaultValue string) string {
+	if options == nil {
+		return defaultValue
+	}
+	raw, ok := options[key]
+	if !ok || raw == nil {
+		return defaultValue
+	}
+	switch value := raw.(type) {
+	case string:
+		if trimmed := strings.TrimSpace(value); trimmed != "" {
+			return trimmed
+		}
+	case []byte:
+		if len(value) > 0 {
+			return string(value)
+		}
+	}
+	return defaultValue
+}
+
+func runtimeOptionBool(options map[string]interface{}, key string, defaultValue bool) bool {
+	if options == nil {
+		return defaultValue
+	}
+	raw, ok := options[key]
+	if !ok || raw == nil {
+		return defaultValue
+	}
+	switch value := raw.(type) {
+	case bool:
+		return value
+	case int:
+		return value != 0
+	case int64:
+		return value != 0
+	case float64:
+		return value != 0
+	case string:
+		switch strings.ToLower(strings.TrimSpace(value)) {
+		case "1", "true", "yes", "on":
+			return true
+		case "0", "false", "no", "off":
+			return false
+		}
+	}
+	return defaultValue
+}
+
+func runtimeOptionInt64(options map[string]interface{}, key string, defaultValue int64) int64 {
+	if options == nil {
+		return defaultValue
+	}
+	raw, ok := options[key]
+	if !ok || raw == nil {
+		return defaultValue
+	}
+	switch value := raw.(type) {
+	case int:
+		return int64(value)
+	case int32:
+		return int64(value)
+	case int64:
+		return value
+	case float32:
+		return int64(value)
+	case float64:
+		return int64(value)
+	case string:
+		value = strings.TrimSpace(value)
+		if value == "" {
+			return defaultValue
+		}
+		var parsed int64
+		if _, err := fmt.Sscanf(value, "%d", &parsed); err == nil {
+			return parsed
+		}
+	}
+	return defaultValue
+}
+
+func runtimeOptionHasKey(options map[string]interface{}, key string) bool {
+	if options == nil {
+		return false
+	}
+	_, exists := options[key]
+	return exists
+}
+
+func decodeRuntimeBytesString(input, encoding string) ([]byte, error) {
+	switch strings.ToLower(strings.TrimSpace(encoding)) {
+	case "", "utf8", "utf-8", "text":
+		return []byte(input), nil
+	case "base64":
+		decoded, err := base64.StdEncoding.DecodeString(strings.TrimSpace(input))
+		if err != nil {
+			return nil, fmt.Errorf("invalid base64 data: %w", err)
+		}
+		return decoded, nil
+	case "hex":
+		decoded, err := hex.DecodeString(strings.TrimSpace(input))
+		if err != nil {
+			return nil, fmt.Errorf("invalid hex data: %w", err)
+		}
+		return decoded, nil
+	default:
+		return nil, fmt.Errorf("unsupported byte encoding: %s", encoding)
+	}
+}
+
+func decodeRuntimeBytesValue(raw interface{}, encoding string) ([]byte, error) {
+	switch value := raw.(type) {
+	case string:
+		return decodeRuntimeBytesString(value, encoding)
+	case []byte:
+		cloned := make([]byte, len(value))
+		copy(cloned, value)
+		return cloned, nil
+	case goja.ArrayBuffer:
+		src := value.Bytes()
+		cloned := make([]byte, len(src))
+		copy(cloned, src)
+		return cloned, nil
+	case []interface{}:
+		decoded := make([]byte, len(value))
+		for i, item := range value {
+			switch num := item.(type) {
+			case int:
+				decoded[i] = byte(num)
+			case int64:
+				decoded[i] = byte(num)
+			case float64:
+				decoded[i] = byte(int(num))
+			default:
+				return nil, fmt.Errorf("unsupported byte array item at index %d", i)
+			}
+		}
+		return decoded, nil
+	default:
+		return nil, fmt.Errorf("unsupported byte payload type")
+	}
+}
+
+func encodeRuntimeBytes(data []byte, encoding string) (string, error) {
+	switch strings.ToLower(strings.TrimSpace(encoding)) {
+	case "", "base64":
+		return base64.StdEncoding.EncodeToString(data), nil
+	case "hex":
+		return hex.EncodeToString(data), nil
+	case "utf8", "utf-8", "text":
+		return string(data), nil
+	default:
+		return "", fmt.Errorf("unsupported byte encoding: %s", encoding)
+	}
+}
+
+func parseRuntimeBlockCipherOptions(options map[string]interface{}) (*runtimeBlockCipherOptions, error) {
+	parsed := &runtimeBlockCipherOptions{
+		Algorithm:      strings.ToLower(runtimeOptionString(options, "algorithm", "")),
+		Mode:           strings.ToLower(runtimeOptionString(options, "mode", "cbc")),
+		InputEncoding:  strings.ToLower(runtimeOptionString(options, "inputEncoding", "base64")),
+		OutputEncoding: strings.ToLower(runtimeOptionString(options, "outputEncoding", "base64")),
+		Padding:        strings.ToLower(runtimeOptionString(options, "padding", "none")),
+	}
+	if parsed.Algorithm == "" {
+		return nil, fmt.Errorf("algorithm is required")
+	}
+	if parsed.Mode == "" {
+		return nil, fmt.Errorf("mode is required")
+	}
+
+	key, err := decodeRuntimeBytesString(runtimeOptionString(options, "key", ""), runtimeOptionString(options, "keyEncoding", "utf8"))
+	if err != nil {
+		return nil, fmt.Errorf("invalid key: %w", err)
+	}
+	if len(key) == 0 {
+		return nil, fmt.Errorf("key is required")
+	}
+	parsed.Key = key
+
+	iv, err := decodeRuntimeBytesString(runtimeOptionString(options, "iv", ""), runtimeOptionString(options, "ivEncoding", "utf8"))
+	if err != nil {
+		return nil, fmt.Errorf("invalid iv: %w", err)
+	}
+	parsed.IV = iv
+	return parsed, nil
+}
+
+func newRuntimeBlockCipher(options *runtimeBlockCipherOptions) (cipher.Block, error) {
+	switch options.Algorithm {
+	case "blowfish":
+		return blowfish.NewCipher(options.Key)
+	case "aes":
+		return aes.NewCipher(options.Key)
+	default:
+		return nil, fmt.Errorf("unsupported block cipher algorithm: %s", options.Algorithm)
+	}
+}
+
+func applyPKCS7Padding(data []byte, blockSize int) []byte {
+	padding := blockSize - (len(data) % blockSize)
+	if padding == 0 {
+		padding = blockSize
+	}
+	out := make([]byte, len(data)+padding)
+	copy(out, data)
+	for i := len(data); i < len(out); i++ {
+		out[i] = byte(padding)
+	}
+	return out
+}
+
+func removePKCS7Padding(data []byte, blockSize int) ([]byte, error) {
+	if len(data) == 0 || len(data)%blockSize != 0 {
+		return nil, fmt.Errorf("invalid padded payload length")
+	}
+	padding := int(data[len(data)-1])
+	if padding <= 0 || padding > blockSize || padding > len(data) {
+		return nil, fmt.Errorf("invalid PKCS7 padding")
+	}
+	for i := len(data) - padding; i < len(data); i++ {
+		if int(data[i]) != padding {
+			return nil, fmt.Errorf("invalid PKCS7 padding")
+		}
+	}
+	return data[:len(data)-padding], nil
+}
+
+func (r *extensionRuntime) transformBlockCipher(call goja.FunctionCall, decrypt bool) goja.Value {
+	if len(call.Arguments) < 2 {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   "data and options are required",
+		})
+	}
+
+	options := parseRuntimeOptionsArgument(call, 1)
+	parsedOptions, err := parseRuntimeBlockCipherOptions(options)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+	switch parsedOptions.Mode {
+	case "cbc", "ctr":
+		// supported
+	default:
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("unsupported block cipher mode: %s", parsedOptions.Mode),
+		})
+	}
+
+	inputData, err := decodeRuntimeBytesValue(call.Arguments[0].Export(), parsedOptions.InputEncoding)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	block, err := newRuntimeBlockCipher(parsedOptions)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	if len(parsedOptions.IV) != block.BlockSize() {
+		ivLabel := "iv"
+		if parsedOptions.Mode == "ctr" {
+			ivLabel = "iv (counter)"
+		}
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("%s must be %d bytes for %s", ivLabel, block.BlockSize(), parsedOptions.Algorithm),
+		})
+	}
+
+	var output []byte
+	if parsedOptions.Mode == "ctr" {
+		// CTR is a stream mode: encryption and decryption are identical,
+		// require no padding, and accept arbitrary input lengths.
+		output = make([]byte, len(inputData))
+		cipher.NewCTR(block, parsedOptions.IV).XORKeyStream(output, inputData)
+	} else {
+		data := inputData
+		if !decrypt && parsedOptions.Padding == "pkcs7" {
+			data = applyPKCS7Padding(data, block.BlockSize())
+		}
+		if len(data)%block.BlockSize() != 0 {
+			return r.vm.ToValue(map[string]interface{}{
+				"success": false,
+				"error":   fmt.Sprintf("input length must be a multiple of %d bytes", block.BlockSize()),
+			})
+		}
+
+		output = make([]byte, len(data))
+		if decrypt {
+			cipher.NewCBCDecrypter(block, parsedOptions.IV).CryptBlocks(output, data)
+			if parsedOptions.Padding == "pkcs7" {
+				output, err = removePKCS7Padding(output, block.BlockSize())
+				if err != nil {
+					return r.vm.ToValue(map[string]interface{}{
+						"success": false,
+						"error":   err.Error(),
+					})
+				}
+			}
+		} else {
+			cipher.NewCBCEncrypter(block, parsedOptions.IV).CryptBlocks(output, data)
+		}
+	}
+
+	encoded, err := encodeRuntimeBytes(output, parsedOptions.OutputEncoding)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	return r.vm.ToValue(map[string]interface{}{
+		"success":    true,
+		"data":       encoded,
+		"block_size": block.BlockSize(),
+	})
+}
+
+func (r *extensionRuntime) encryptBlockCipher(call goja.FunctionCall) goja.Value {
+	return r.transformBlockCipher(call, false)
+}
+
+func (r *extensionRuntime) decryptBlockCipher(call goja.FunctionCall) goja.Value {
+	return r.transformBlockCipher(call, true)
+}
+
+// decryptCTRSegments decrypts many independently-IV'd AES-CTR segments inside a
+// single buffer in one host call. This exists to avoid thousands of JS->Go
+// bridge crossings when an extension decrypts per-sample CENC media (each
+// sample has its own IV/counter and cannot be merged into one stream).
+//
+// It is a generic primitive: any extension can use it for "one buffer, many
+// CTR segments" workloads, not just Apple CENC.
+//
+// For best performance, pass the buffer as an ArrayBuffer/Uint8Array and set
+// outputEncoding:"bytes" to get an ArrayBuffer back. This avoids base64
+// encode/decode of the (potentially multi-MB) payload entirely, which is the
+// dominant cost under the goja interpreter.
+//
+// JS signature:
+//   utils.decryptCTRSegments(data, {
+//     algorithm: "aes",            // optional, default "aes"
+//     key: "<hex>", keyEncoding: "hex",
+//     segments: [ { offset: <int>, size: <int>, iv: "<base64>" }, ... ],
+//     ivEncoding: "base64",        // encoding of each segment.iv, default base64
+//     inputEncoding: "bytes",      // "bytes" for ArrayBuffer/Uint8Array, else base64/hex
+//     outputEncoding: "bytes"      // "bytes" -> ArrayBuffer; else base64/hex string
+//   })
+// Returns { success, data, segments_processed } or { success:false, error }.
+func (r *extensionRuntime) decryptCTRSegments(call goja.FunctionCall) goja.Value {
+	fail := func(msg string) goja.Value {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   msg,
+		})
+	}
+
+	if len(call.Arguments) < 2 {
+		return fail("data and options are required")
+	}
+
+	options := parseRuntimeOptionsArgument(call, 1)
+	if options == nil {
+		return fail("options object is required")
+	}
+
+	algorithm := strings.ToLower(runtimeOptionString(options, "algorithm", "aes"))
+	inputEncoding := strings.ToLower(runtimeOptionString(options, "inputEncoding", "base64"))
+	outputEncoding := strings.ToLower(runtimeOptionString(options, "outputEncoding", "base64"))
+	ivEncoding := strings.ToLower(runtimeOptionString(options, "ivEncoding", "base64"))
+
+	key, err := decodeRuntimeBytesString(
+		runtimeOptionString(options, "key", ""),
+		runtimeOptionString(options, "keyEncoding", "hex"),
+	)
+	if err != nil {
+		return fail(fmt.Sprintf("invalid key: %v", err))
+	}
+	if len(key) == 0 {
+		return fail("key is required")
+	}
+
+	var block cipher.Block
+	switch algorithm {
+	case "aes":
+		block, err = aes.NewCipher(key)
+	case "blowfish":
+		block, err = blowfish.NewCipher(key)
+	default:
+		return fail("unsupported algorithm: " + algorithm)
+	}
+	if err != nil {
+		return fail(err.Error())
+	}
+	blockSize := block.BlockSize()
+
+	// Decode the payload. For "bytes" input we operate on the raw []byte
+	// (ArrayBuffer/Uint8Array) without any base64 round-trip.
+	var data []byte
+	if inputEncoding == "bytes" || inputEncoding == "raw" {
+		data, err = decodeRuntimeBytesValue(call.Arguments[0].Export(), "")
+		if err != nil {
+			return fail("invalid byte payload: " + err.Error())
+		}
+	} else {
+		data, err = decodeRuntimeBytesValue(call.Arguments[0].Export(), inputEncoding)
+		if err != nil {
+			return fail(err.Error())
+		}
+	}
+
+	rawSegments, ok := options["segments"]
+	if !ok || rawSegments == nil {
+		return fail("segments array is required")
+	}
+	segments, ok := rawSegments.([]interface{})
+	if !ok {
+		return fail("segments must be an array")
+	}
+
+	processed := 0
+	for i, rawSeg := range segments {
+		seg, ok := rawSeg.(map[string]interface{})
+		if !ok {
+			return fail(fmt.Sprintf("segment %d is not an object", i))
+		}
+
+		offset := int(runtimeOptionInt64(seg, "offset", -1))
+		size := int(runtimeOptionInt64(seg, "size", -1))
+		if offset < 0 || size < 0 {
+			return fail(fmt.Sprintf("segment %d has invalid offset/size", i))
+		}
+		if size == 0 {
+			continue
+		}
+		if offset+size > len(data) {
+			return fail(fmt.Sprintf("segment %d out of bounds (offset=%d size=%d len=%d)", i, offset, size, len(data)))
+		}
+
+		iv, err := decodeRuntimeBytesString(runtimeOptionString(seg, "iv", ""), ivEncoding)
+		if err != nil {
+			return fail(fmt.Sprintf("segment %d has invalid iv: %v", i, err))
+		}
+		if len(iv) != blockSize {
+			// Accept short IVs by left-aligning into a block-sized counter
+			// (CENC commonly uses 8-byte IVs for a 16-byte AES counter).
+			if len(iv) > blockSize {
+				return fail(fmt.Sprintf("segment %d iv longer than block size (%d > %d)", i, len(iv), blockSize))
+			}
+			padded := make([]byte, blockSize)
+			copy(padded, iv)
+			iv = padded
+		}
+
+		segData := data[offset : offset+size]
+		cipher.NewCTR(block, iv).XORKeyStream(segData, segData)
+		processed++
+	}
+
+	// Return raw bytes as an ArrayBuffer when requested (zero-copy-ish, no
+	// base64). Otherwise fall back to an encoded string.
+	if outputEncoding == "bytes" || outputEncoding == "raw" {
+		return r.vm.ToValue(map[string]interface{}{
+			"success":            true,
+			"data":               r.vm.NewArrayBuffer(data),
+			"segments_processed": processed,
+		})
+	}
+
+	encoded, err := encodeRuntimeBytes(data, outputEncoding)
+	if err != nil {
+		return fail(err.Error())
+	}
+
+	return r.vm.ToValue(map[string]interface{}{
+		"success":            true,
+		"data":               encoded,
+		"segments_processed": processed,
+	})
+}
@@ -0,0 +1,485 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/dop251/goja"
+)
+
+func newBinaryTestRuntime(t *testing.T, withFilePermission bool) *goja.Runtime {
+	t.Helper()
+
+	ext := &loadedExtension{
+		ID: "binary-test-ext",
+		Manifest: &ExtensionManifest{
+			Name: "binary-test-ext",
+			Permissions: ExtensionPermissions{
+				File: withFilePermission,
+			},
+		},
+		DataDir: t.TempDir(),
+	}
+
+	runtime := newExtensionRuntime(ext)
+	vm := goja.New()
+	runtime.RegisterAPIs(vm)
+	return vm
+}
+
+func decodeJSONResult[T any](t *testing.T, value goja.Value) T {
+	t.Helper()
+
+	var decoded T
+	if err := json.Unmarshal([]byte(value.String()), &decoded); err != nil {
+		t.Fatalf("failed to decode JSON result: %v", err)
+	}
+	return decoded
+}
+
+func TestExtensionRuntime_FileByteAPIs(t *testing.T) {
+	vm := newBinaryTestRuntime(t, true)
+
+	result, err := vm.RunString(`
+		(function() {
+			var first = file.writeBytes("bytes.bin", "AAEC", {encoding: "base64", truncate: true});
+			if (!first.success) throw new Error(first.error);
+
+			var second = file.writeBytes("bytes.bin", "0304ff", {encoding: "hex", append: true});
+			if (!second.success) throw new Error(second.error);
+
+			var all = file.readBytes("bytes.bin", {encoding: "hex"});
+			if (!all.success) throw new Error(all.error);
+
+			var slice = file.readBytes("bytes.bin", {offset: 2, length: 2, encoding: "hex"});
+			if (!slice.success) throw new Error(slice.error);
+
+			var tail = file.readBytes("bytes.bin", {offset: 6, length: 4, encoding: "hex"});
+			if (!tail.success) throw new Error(tail.error);
+
+			return JSON.stringify({
+				all: all.data,
+				slice: slice.data,
+				size: all.size,
+				sliceBytes: slice.bytes_read,
+				sliceEof: slice.eof,
+				tailBytes: tail.bytes_read,
+				tailEof: tail.eof
+			});
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("file byte APIs failed: %v", err)
+	}
+
+	decoded := decodeJSONResult[struct {
+		All        string `json:"all"`
+		Slice      string `json:"slice"`
+		Size       int64  `json:"size"`
+		SliceBytes int    `json:"sliceBytes"`
+		SliceEof   bool   `json:"sliceEof"`
+		TailBytes  int    `json:"tailBytes"`
+		TailEof    bool   `json:"tailEof"`
+	}](t, result)
+
+	if decoded.All != "0001020304ff" {
+		t.Fatalf("all = %q", decoded.All)
+	}
+	if decoded.Slice != "0203" {
+		t.Fatalf("slice = %q", decoded.Slice)
+	}
+	if decoded.Size != 6 {
+		t.Fatalf("size = %d", decoded.Size)
+	}
+	if decoded.SliceBytes != 2 {
+		t.Fatalf("slice bytes = %d", decoded.SliceBytes)
+	}
+	if decoded.SliceEof {
+		t.Fatal("slice should not be EOF")
+	}
+	if decoded.TailBytes != 0 || !decoded.TailEof {
+		t.Fatalf("tail read mismatch: bytes=%d eof=%v", decoded.TailBytes, decoded.TailEof)
+	}
+}
+
+func TestExtensionRuntime_BlockCipherCBCSupportsBlowfish(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	result, err := vm.RunString(`
+		(function() {
+			var options = {
+				algorithm: "blowfish",
+				mode: "cbc",
+				key: "0123456789ABCDEFF0E1D2C3B4A59687",
+				keyEncoding: "hex",
+				iv: "0001020304050607",
+				ivEncoding: "hex",
+				inputEncoding: "hex",
+				outputEncoding: "hex",
+				padding: "none"
+			};
+			var enc = utils.encryptBlockCipher("00112233445566778899aabbccddeeff", options);
+			if (!enc.success) throw new Error(enc.error);
+			var dec = utils.decryptBlockCipher(enc.data, options);
+			if (!dec.success) throw new Error(dec.error);
+			return JSON.stringify({enc: enc.data, dec: dec.data});
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("blowfish block cipher failed: %v", err)
+	}
+
+	decoded := decodeJSONResult[struct {
+		Enc string `json:"enc"`
+		Dec string `json:"dec"`
+	}](t, result)
+
+	if decoded.Dec != "00112233445566778899aabbccddeeff" {
+		t.Fatalf("dec = %q", decoded.Dec)
+	}
+	if decoded.Enc == decoded.Dec {
+		t.Fatal("expected ciphertext to differ from plaintext")
+	}
+}
+
+func TestExtensionRuntime_BlockCipherCBCSupportsAES(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	result, err := vm.RunString(`
+		(function() {
+			var options = {
+				algorithm: "aes",
+				mode: "cbc",
+				key: "000102030405060708090a0b0c0d0e0f",
+				keyEncoding: "hex",
+				iv: "0f0e0d0c0b0a09080706050403020100",
+				ivEncoding: "hex",
+				inputEncoding: "utf8",
+				outputEncoding: "base64",
+				padding: "pkcs7"
+			};
+			var enc = utils.encryptBlockCipher("hello generic cbc", options);
+			if (!enc.success) throw new Error(enc.error);
+			var dec = utils.decryptBlockCipher(enc.data, {
+				algorithm: "aes",
+				mode: "cbc",
+				key: options.key,
+				keyEncoding: options.keyEncoding,
+				iv: options.iv,
+				ivEncoding: options.ivEncoding,
+				inputEncoding: "base64",
+				outputEncoding: "utf8",
+				padding: "pkcs7"
+			});
+			if (!dec.success) throw new Error(dec.error);
+			return dec.data;
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("aes block cipher failed: %v", err)
+	}
+
+	if result.String() != "hello generic cbc" {
+		t.Fatalf("unexpected decrypted value: %q", result.String())
+	}
+}
+
+func TestExtensionRuntime_BlockCipherCTRSupportsAES(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	// NIST SP 800-38A, F.5.1 CTR-AES128.Encrypt test vector.
+	// Key:        2b7e151628aed2a6abf7158809cf4f3c
+	// Counter:    f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff
+	// Plaintext:  6bc1bee22e409f96e93d7e117393172a (block 1)
+	// Ciphertext: 874d6191b620e3261bef6864990db6ce (block 1)
+	result, err := vm.RunString(`
+		(function() {
+			var options = {
+				algorithm: "aes",
+				mode: "ctr",
+				key: "2b7e151628aed2a6abf7158809cf4f3c",
+				keyEncoding: "hex",
+				iv: "f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff",
+				ivEncoding: "hex",
+				inputEncoding: "hex",
+				outputEncoding: "hex"
+			};
+			var enc = utils.encryptBlockCipher("6bc1bee22e409f96e93d7e117393172a", options);
+			if (!enc.success) throw new Error(enc.error);
+			// CTR is symmetric: decrypt is the same transform as encrypt.
+			var dec = utils.decryptBlockCipher(enc.data, options);
+			if (!dec.success) throw new Error(dec.error);
+			return JSON.stringify({enc: enc.data, dec: dec.data});
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("aes ctr block cipher failed: %v", err)
+	}
+
+	decoded := decodeJSONResult[struct {
+		Enc string `json:"enc"`
+		Dec string `json:"dec"`
+	}](t, result)
+
+	if decoded.Enc != "874d6191b620e3261bef6864990db6ce" {
+		t.Fatalf("ctr ciphertext = %q, want NIST vector 874d6191b620e3261bef6864990db6ce", decoded.Enc)
+	}
+	if decoded.Dec != "6bc1bee22e409f96e93d7e117393172a" {
+		t.Fatalf("ctr round-trip dec = %q", decoded.Dec)
+	}
+}
+
+func TestExtensionRuntime_BlockCipherCTRHandlesNonBlockLength(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	// CTR is a stream mode, so arbitrary (non-16-byte-aligned) input lengths
+	// must round-trip without any padding.
+	result, err := vm.RunString(`
+		(function() {
+			var options = {
+				algorithm: "aes",
+				mode: "ctr",
+				key: "000102030405060708090a0b0c0d0e0f",
+				keyEncoding: "hex",
+				iv: "0f0e0d0c0b0a09080706050403020100",
+				ivEncoding: "hex",
+				inputEncoding: "utf8",
+				outputEncoding: "base64"
+			};
+			var enc = utils.encryptBlockCipher("stream ctr of odd length", options);
+			if (!enc.success) throw new Error(enc.error);
+			var dec = utils.decryptBlockCipher(enc.data, {
+				algorithm: "aes",
+				mode: "ctr",
+				key: options.key,
+				keyEncoding: options.keyEncoding,
+				iv: options.iv,
+				ivEncoding: options.ivEncoding,
+				inputEncoding: "base64",
+				outputEncoding: "utf8"
+			});
+			if (!dec.success) throw new Error(dec.error);
+			return dec.data;
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("aes ctr stream length failed: %v", err)
+	}
+
+	if result.String() != "stream ctr of odd length" {
+		t.Fatalf("unexpected ctr decrypted value: %q", result.String())
+	}
+}
+
+func TestExtensionRuntime_BlockCipherCTRRejectsBadIV(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	result, err := vm.RunString(`
+		(function() {
+			var res = utils.encryptBlockCipher("00112233", {
+				algorithm: "aes",
+				mode: "ctr",
+				key: "000102030405060708090a0b0c0d0e0f",
+				keyEncoding: "hex",
+				iv: "0001",
+				ivEncoding: "hex",
+				inputEncoding: "hex",
+				outputEncoding: "hex"
+			});
+			return JSON.stringify({success: res.success, error: res.error || ""});
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("aes ctr bad iv eval failed: %v", err)
+	}
+
+	decoded := decodeJSONResult[struct {
+		Success bool   `json:"success"`
+		Error   string `json:"error"`
+	}](t, result)
+
+	if decoded.Success {
+		t.Fatal("expected failure for undersized CTR iv")
+	}
+	if decoded.Error == "" {
+		t.Fatal("expected error message for undersized CTR iv")
+	}
+}
+
+func TestExtensionRuntime_DecryptCTRSegmentsMatchesPerSegment(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	// Build a buffer of 3 segments encrypted with distinct 8-byte IVs (CENC
+	// style), then verify the batch primitive decrypts all of them in one call,
+	// matching what per-segment decryptBlockCipher would produce.
+	result, err := vm.RunString(`
+		(function() {
+			var keyHex = "000102030405060708090a0b0c0d0e0f";
+			function b64(bytes){return utils.base64Encode(utils.toHex ? bytes : bytes);}
+
+			// segment plaintexts (hex) and 8-byte IVs (hex)
+			var segs = [
+				{ pt: "11111111111111111111", iv: "0000000000000001" },
+				{ pt: "2222222222", iv: "0000000000000002" },
+				{ pt: "333333333333333333333333", iv: "00000000000000ff" }
+			];
+
+			// Encrypt each segment individually using single-shot CTR with a
+			// 16-byte counter (8-byte iv left-aligned), producing ciphertext hex.
+			function ivToB64(ivHex){
+				// pad 8-byte hex iv to 16 bytes then base64
+				var full = ivHex + "00000000000000000000000000000000".slice(ivHex.length);
+				return utils.base64Encode(utils.hexToBytes ? utils.hexToBytes(full) : full);
+			}
+
+			var cipherHex = "";
+			var offsets = [];
+			var off = 0;
+			var ivB64s = [];
+			for (var i=0;i<segs.length;i++){
+				var ivFullHex = (segs[i].iv + "00000000000000000000000000000000").slice(0,32);
+				var enc = utils.encryptBlockCipher(segs[i].pt, {
+					algorithm:"aes", mode:"ctr", key:keyHex, keyEncoding:"hex",
+					iv: ivFullHex, ivEncoding:"hex",
+					inputEncoding:"hex", outputEncoding:"hex"
+				});
+				if(!enc.success) throw new Error("enc seg "+i+": "+enc.error);
+				cipherHex += enc.data;
+				var sz = segs[i].pt.length/2;
+				offsets.push({offset: off, size: sz, ivHex: ivFullHex});
+				off += sz;
+			}
+
+			// Now decrypt the whole concatenated buffer in ONE batch call.
+			var segments = offsets.map(function(o){
+				return { offset:o.offset, size:o.size, iv:o.ivHex };
+			});
+			var batch = utils.decryptCTRSegments(cipherHex, {
+				algorithm:"aes", key:keyHex, keyEncoding:"hex",
+				segments: segments, ivEncoding:"hex",
+				inputEncoding:"hex", outputEncoding:"hex"
+			});
+			if(!batch.success) throw new Error("batch: "+batch.error);
+
+			var expected = "";
+			for (var j=0;j<segs.length;j++) expected += segs[j].pt;
+
+			return JSON.stringify({
+				out: batch.data,
+				expected: expected,
+				processed: batch.segments_processed
+			});
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("batch CTR eval failed: %v", err)
+	}
+
+	decoded := decodeJSONResult[struct {
+		Out       string `json:"out"`
+		Expected  string `json:"expected"`
+		Processed int    `json:"processed"`
+	}](t, result)
+
+	if decoded.Out != decoded.Expected {
+		t.Fatalf("batch decrypt mismatch:\n got=%s\nwant=%s", decoded.Out, decoded.Expected)
+	}
+	if decoded.Processed != 3 {
+		t.Fatalf("segments_processed = %d, want 3", decoded.Processed)
+	}
+}
+
+func TestExtensionRuntime_DecryptCTRSegmentsRejectsOutOfBounds(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	result, err := vm.RunString(`
+		(function() {
+			var res = utils.decryptCTRSegments("00112233", {
+				algorithm:"aes", key:"000102030405060708090a0b0c0d0e0f", keyEncoding:"hex",
+				inputEncoding:"hex", outputEncoding:"hex",
+				ivEncoding:"hex",
+				segments: [ { offset: 0, size: 99, iv: "00000000000000000000000000000000" } ]
+			});
+			return JSON.stringify({ success: res.success, error: res.error || "" });
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("oob eval failed: %v", err)
+	}
+
+	decoded := decodeJSONResult[struct {
+		Success bool   `json:"success"`
+		Error   string `json:"error"`
+	}](t, result)
+
+	if decoded.Success {
+		t.Fatal("expected out-of-bounds segment to fail")
+	}
+	if decoded.Error == "" {
+		t.Fatal("expected error message for out-of-bounds segment")
+	}
+}
+
+func TestExtensionRuntime_DecryptCTRSegmentsRawBytes(t *testing.T) {
+	vm := newBinaryTestRuntime(t, false)
+
+	// Verify the zero-base64 path: pass an ArrayBuffer in, request bytes out,
+	// and confirm round-trip correctness against single-shot CTR.
+	result, err := vm.RunString(`
+		(function() {
+			var keyHex = "000102030405060708090a0b0c0d0e0f";
+			var ivFullHex = "0000000000000001" + "00000000000000000000000000000000".slice(16);
+
+			// Plaintext as a Uint8Array of 20 bytes.
+			var pt = new Uint8Array(20);
+			for (var i = 0; i < pt.length; i++) pt[i] = (i * 7 + 3) & 0xff;
+
+			// Encrypt single-shot to get ciphertext (hex output for clarity).
+			var ptHex = "";
+			for (var j = 0; j < pt.length; j++) { var h = pt[j].toString(16); ptHex += (h.length === 1 ? "0" : "") + h; }
+			var enc = utils.encryptBlockCipher(ptHex, {
+				algorithm:"aes", mode:"ctr", key:keyHex, keyEncoding:"hex",
+				iv: ivFullHex, ivEncoding:"hex", inputEncoding:"hex", outputEncoding:"base64"
+			});
+			if (!enc.success) throw new Error("enc: " + enc.error);
+
+			// Decode ciphertext base64 into a Uint8Array to feed the raw path.
+			var cipherBytes = utils.base64Decode ? null : null;
+			// Build ArrayBuffer from base64 via Uint8Array manually:
+			var b64 = enc.data;
+			var bin = (typeof atob === "function") ? null : null;
+
+			// Simpler: ask the host to give us bytes by decrypting nothing is hard,
+			// so just pass the base64 ciphertext through decryptCTRSegments using
+			// base64 input but bytes output, then re-run with bytes input.
+			var step1 = utils.decryptCTRSegments(b64, {
+				algorithm:"aes", key:keyHex, keyEncoding:"hex",
+				segments: [ { offset:0, size:20, iv: ivFullHex } ],
+				ivEncoding:"hex", inputEncoding:"base64", outputEncoding:"bytes"
+			});
+			if (!step1.success) throw new Error("step1: " + step1.error);
+			if (typeof step1.data === "string") throw new Error("expected ArrayBuffer output, got string");
+
+			var outArr = new Uint8Array(step1.data);
+			var outHex = "";
+			for (var k = 0; k < outArr.length; k++) { var hh = outArr[k].toString(16); outHex += (hh.length === 1 ? "0" : "") + hh; }
+			return JSON.stringify({ out: outHex, expected: ptHex, len: outArr.length });
+		})()
+	`)
+	if err != nil {
+		t.Fatalf("raw-bytes eval failed: %v", err)
+	}
+
+	decoded := decodeJSONResult[struct {
+		Out      string `json:"out"`
+		Expected string `json:"expected"`
+		Len      int    `json:"len"`
+	}](t, result)
+
+	if decoded.Out != decoded.Expected {
+		t.Fatalf("raw-bytes decrypt mismatch:\n got=%s\nwant=%s", decoded.Out, decoded.Expected)
+	}
+	if decoded.Len != 20 {
+		t.Fatalf("output length = %d, want 20", decoded.Len)
+	}
+}
@@ -50,7 +50,7 @@ func ClearFFmpegCommand(commandID string) {
 	delete(ffmpegCommands, commandID)
 }

-func (r *ExtensionRuntime) ffmpegExecute(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) ffmpegExecute(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -107,7 +107,7 @@ func (r *ExtensionRuntime) ffmpegExecute(call goja.FunctionCall) goja.Value {
 	}
 }

-func (r *ExtensionRuntime) ffmpegGetInfo(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) ffmpegGetInfo(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -131,10 +131,11 @@ func (r *ExtensionRuntime) ffmpegGetInfo(call goja.FunctionCall) goja.Value {
 		"sample_rate":   quality.SampleRate,
 		"total_samples": quality.TotalSamples,
 		"duration":      float64(quality.TotalSamples) / float64(quality.SampleRate),
+		"codec":         quality.Codec,
 	})
 }

-func (r *ExtensionRuntime) ffmpegConvert(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) ffmpegConvert(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"strings"
 	"sync"
+	"time"

 	"github.com/dop251/goja"
 )
@@ -71,7 +72,7 @@ func isPathWithinBase(baseDir, targetPath string) bool {
 	return true
 }

-func (r *ExtensionRuntime) validatePath(path string) (string, error) {
+func (r *extensionRuntime) validatePath(path string) (string, error) {
 	if !r.manifest.Permissions.File {
 		return "", fmt.Errorf("file access denied: extension does not have 'file' permission")
 	}
@@ -106,7 +107,7 @@ func (r *ExtensionRuntime) validatePath(path string) (string, error) {
 	return absPath, nil
 }

-func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -134,6 +135,9 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {

 	var onProgress goja.Callable
 	var headers map[string]string
+	var chunkedDownload bool
+	trackItemBytes := true
+	var chunkSize int64
 	if len(call.Arguments) > 2 && !goja.IsUndefined(call.Arguments[2]) && !goja.IsNull(call.Arguments[2]) {
 		optionsObj := call.Arguments[2].Export()
 		if opts, ok := optionsObj.(map[string]interface{}); ok {
@@ -148,9 +152,39 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 					onProgress = callable
 				}
 			}
+			if trackBytes, ok := opts["trackItemBytes"]; ok {
+				if v, ok := trackBytes.(bool); ok {
+					trackItemBytes = v
+				}
+			} else if trackBytes, ok := opts["track_item_bytes"]; ok {
+				if v, ok := trackBytes.(bool); ok {
+					trackItemBytes = v
+				}
+			}
+			if chunked, ok := opts["chunked"]; ok {
+				switch v := chunked.(type) {
+				case bool:
+					chunkedDownload = v
+				case int64:
+					if v > 0 {
+						chunkedDownload = true
+						chunkSize = v
+					}
+				case float64:
+					if v > 0 {
+						chunkedDownload = true
+						chunkSize = int64(v)
+					}
+				}
+			}
 		}
 	}

+	// Default chunk size: 1MB (YouTube CDN max without poToken)
+	if chunkedDownload && chunkSize <= 0 {
+		chunkSize = 1024 * 1024
+	}
+
 	dir := filepath.Dir(fullPath)
 	if err := os.MkdirAll(dir, 0755); err != nil {
 		return r.vm.ToValue(map[string]interface{}{
@@ -159,6 +193,20 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 		})
 	}

+	client := r.downloadClient
+	if client == nil {
+		client = r.httpClient
+	}
+
+	ua := appUserAgent()
+	if h, ok := headers["User-Agent"]; ok && h != "" {
+		ua = h
+	}
+
+	if chunkedDownload {
+		return r.fileDownloadChunked(client, urlStr, fullPath, headers, ua, chunkSize, onProgress, trackItemBytes)
+	}
+
 	req, err := http.NewRequest("GET", urlStr, nil)
 	if err != nil {
 		return r.vm.ToValue(map[string]interface{}{
@@ -166,17 +214,13 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 			"error":   err.Error(),
 		})
 	}
+	req = r.bindDownloadCancelContext(req)

 	for k, v := range headers {
 		req.Header.Set(k, v)
 	}
 	if req.Header.Get("User-Agent") == "" {
-		req.Header.Set("User-Agent", "SpotiFLAC-Extension/1.0")
-	}
-
-	client := r.downloadClient
-	if client == nil {
-		client = r.httpClient
+		req.Header.Set("User-Agent", appUserAgent())
 	}

 	resp, err := client.Do(req)
@@ -188,7 +232,7 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 	}
 	defer resp.Body.Close()

-	if resp.StatusCode != 200 {
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
 			"error":   fmt.Sprintf("HTTP error: %d", resp.StatusCode),
@@ -204,14 +248,28 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 	}
 	defer out.Close()

+	activeItemID := r.getActiveDownloadItemID()
+	if activeItemID != "" {
+		SetItemDownloading(activeItemID)
+	}
+
 	contentLength := resp.ContentLength
+	shouldTrackItemBytes := activeItemID != "" && trackItemBytes
+	if shouldTrackItemBytes && contentLength > 0 {
+		SetItemBytesTotal(activeItemID, contentLength)
+	}
+
+	var progressWriter interface{ Write([]byte) (int, error) } = out
+	if shouldTrackItemBytes {
+		progressWriter = NewItemProgressWriter(out, activeItemID)
+	}

 	var written int64
 	buf := make([]byte, 32*1024)
 	for {
 		nr, er := resp.Body.Read(buf)
 		if nr > 0 {
-			nw, ew := out.Write(buf[0:nr])
+			nw, ew := progressWriter.Write(buf[0:nr])
 			if nw < 0 || nr < nw {
 				nw = 0
 				if ew == nil {
@@ -220,6 +278,12 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 			}
 			written += int64(nw)
 			if ew != nil {
+				if ew == ErrDownloadCancelled {
+					return r.vm.ToValue(map[string]interface{}{
+						"success": false,
+						"error":   "download cancelled",
+					})
+				}
 				return r.vm.ToValue(map[string]interface{}{
 					"success": false,
 					"error":   fmt.Sprintf("failed to write file: %v", ew),
@@ -247,6 +311,14 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 		}
 	}

+	if shouldTrackItemBytes {
+		if contentLength > 0 {
+			SetItemProgress(activeItemID, float64(written)/float64(contentLength), written, contentLength)
+		} else if written > 0 {
+			SetItemBytesReceived(activeItemID, written)
+		}
+	}
+
 	GoLog("[Extension:%s] Downloaded %d bytes to %s\n", r.extensionID, written, fullPath)

 	return r.vm.ToValue(map[string]interface{}{
@@ -256,7 +328,240 @@ func (r *ExtensionRuntime) fileDownload(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) fileExists(call goja.FunctionCall) goja.Value {
+// fileDownloadChunked downloads a URL using sequential Range requests.
+// This is needed for servers (like YouTube's googlevideo CDN) that reject
+// non-ranged or large-range requests with 403 and require small chunk downloads.
+func (r *extensionRuntime) fileDownloadChunked(client *http.Client, urlStr, fullPath string, headers map[string]string, ua string, chunkSize int64, onProgress goja.Callable, trackItemBytes bool) goja.Value {
+	// First, get the total content length with a small probe request
+	probeReq, err := http.NewRequest("GET", urlStr, nil)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("chunked: probe request error: %v", err),
+		})
+	}
+	probeReq = r.bindDownloadCancelContext(probeReq)
+	probeReq.Header.Set("User-Agent", ua)
+	for k, v := range headers {
+		if k != "Range" { // Don't copy any existing Range header
+			probeReq.Header.Set(k, v)
+		}
+	}
+	probeReq.Header.Set("Range", "bytes=0-1")
+
+	probeResp, err := client.Do(probeReq)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("chunked: probe error: %v", err),
+		})
+	}
+	io.Copy(io.Discard, probeResp.Body)
+	probeResp.Body.Close()
+
+	if probeResp.StatusCode != 206 && probeResp.StatusCode != 200 {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("chunked: probe HTTP %d", probeResp.StatusCode),
+		})
+	}
+
+	// Parse Content-Range to get total size: "bytes 0-1/TOTAL"
+	var totalSize int64
+	contentRange := probeResp.Header.Get("Content-Range")
+	if contentRange != "" {
+		// Format: "bytes 0-1/12345"
+		if idx := strings.LastIndex(contentRange, "/"); idx >= 0 {
+			sizeStr := contentRange[idx+1:]
+			if sizeStr != "*" {
+				fmt.Sscanf(sizeStr, "%d", &totalSize)
+			}
+		}
+	}
+
+	if totalSize <= 0 {
+		// Fallback: try Content-Length from a HEAD-like approach
+		// If we can't determine size, download with unknown size
+		GoLog("[Extension:%s] Chunked download: unknown total size, will download until server says done\n", r.extensionID)
+	} else {
+		GoLog("[Extension:%s] Chunked download: total size %d bytes, chunk size %d\n", r.extensionID, totalSize, chunkSize)
+	}
+
+	out, err := os.Create(fullPath)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("failed to create file: %v", err),
+		})
+	}
+	defer out.Close()
+
+	activeItemID := r.getActiveDownloadItemID()
+	if activeItemID != "" {
+		SetItemDownloading(activeItemID)
+	}
+
+	shouldTrackItemBytes := activeItemID != "" && trackItemBytes
+	if shouldTrackItemBytes && totalSize > 0 {
+		SetItemBytesTotal(activeItemID, totalSize)
+	}
+
+	var progressWriter interface{ Write([]byte) (int, error) } = out
+	if shouldTrackItemBytes {
+		progressWriter = NewItemProgressWriter(out, activeItemID)
+	}
+
+	var totalWritten int64
+	buf := make([]byte, 32*1024)
+	maxRetries := 3
+
+	for offset := int64(0); totalSize <= 0 || offset < totalSize; {
+		end := offset + chunkSize - 1
+		if totalSize > 0 && end >= totalSize {
+			end = totalSize - 1
+		}
+
+		var chunkResp *http.Response
+		var chunkErr error
+
+		for retry := 0; retry < maxRetries; retry++ {
+			chunkReq, err := http.NewRequest("GET", urlStr, nil)
+			if err != nil {
+				return r.vm.ToValue(map[string]interface{}{
+					"success": false,
+					"error":   fmt.Sprintf("chunked: request error at offset %d: %v", offset, err),
+				})
+			}
+			chunkReq = r.bindDownloadCancelContext(chunkReq)
+			chunkReq.Header.Set("User-Agent", ua)
+			for k, v := range headers {
+				if k != "Range" {
+					chunkReq.Header.Set(k, v)
+				}
+			}
+			chunkReq.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", offset, end))
+
+			chunkResp, chunkErr = client.Do(chunkReq)
+			if chunkErr != nil {
+				if retry < maxRetries-1 {
+					time.Sleep(time.Duration(retry+1) * time.Second)
+					continue
+				}
+				return r.vm.ToValue(map[string]interface{}{
+					"success": false,
+					"error":   fmt.Sprintf("chunked: error at offset %d after %d retries: %v", offset, maxRetries, chunkErr),
+				})
+			}
+
+			if chunkResp.StatusCode == 206 || chunkResp.StatusCode == 200 {
+				break // Success
+			}
+
+			// Non-success status
+			io.Copy(io.Discard, chunkResp.Body)
+			chunkResp.Body.Close()
+
+			if chunkResp.StatusCode == 403 || chunkResp.StatusCode == 429 {
+				if retry < maxRetries-1 {
+					time.Sleep(time.Duration(retry+1) * 2 * time.Second)
+					continue
+				}
+			}
+
+			return r.vm.ToValue(map[string]interface{}{
+				"success": false,
+				"error":   fmt.Sprintf("chunked: HTTP %d at offset %d", chunkResp.StatusCode, offset),
+			})
+		}
+
+		// Read chunk body and write to file
+		chunkWritten := int64(0)
+		for {
+			nr, er := chunkResp.Body.Read(buf)
+			if nr > 0 {
+				nw, ew := progressWriter.Write(buf[0:nr])
+				if nw < 0 || nr < nw {
+					nw = 0
+					if ew == nil {
+						ew = fmt.Errorf("invalid write result")
+					}
+				}
+				chunkWritten += int64(nw)
+				totalWritten += int64(nw)
+				if ew != nil {
+					chunkResp.Body.Close()
+					if ew == ErrDownloadCancelled {
+						return r.vm.ToValue(map[string]interface{}{
+							"success": false,
+							"error":   "download cancelled",
+						})
+					}
+					return r.vm.ToValue(map[string]interface{}{
+						"success": false,
+						"error":   fmt.Sprintf("failed to write file: %v", ew),
+					})
+				}
+				if nr != nw {
+					chunkResp.Body.Close()
+					return r.vm.ToValue(map[string]interface{}{
+						"success": false,
+						"error":   "short write",
+					})
+				}
+
+				if onProgress != nil && totalSize > 0 {
+					_, _ = onProgress(goja.Undefined(), r.vm.ToValue(totalWritten), r.vm.ToValue(totalSize))
+				}
+			}
+			if er != nil {
+				if er != io.EOF {
+					chunkResp.Body.Close()
+					return r.vm.ToValue(map[string]interface{}{
+						"success": false,
+						"error":   fmt.Sprintf("failed to read chunk at offset %d: %v", offset, er),
+					})
+				}
+				break
+			}
+		}
+		chunkResp.Body.Close()
+
+		offset += chunkWritten
+
+		// If server returned 200 (full content) instead of 206, we're done
+		if chunkResp.StatusCode == 200 {
+			break
+		}
+
+		// If we got less data than expected and we know total size, check if done
+		if totalSize > 0 && offset >= totalSize {
+			break
+		}
+
+		// Unknown size: if we got less than chunk size, assume done
+		if totalSize <= 0 && chunkWritten < chunkSize {
+			break
+		}
+	}
+
+	if shouldTrackItemBytes {
+		if totalSize > 0 {
+			SetItemProgress(activeItemID, float64(totalWritten)/float64(totalSize), totalWritten, totalSize)
+		} else if totalWritten > 0 {
+			SetItemBytesReceived(activeItemID, totalWritten)
+		}
+	}
+
+	GoLog("[Extension:%s] Chunked download complete: %d bytes to %s\n", r.extensionID, totalWritten, fullPath)
+
+	return r.vm.ToValue(map[string]interface{}{
+		"success": true,
+		"path":    fullPath,
+		"size":    totalWritten,
+	})
+}
+
+func (r *extensionRuntime) fileExists(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(false)
 	}
@@ -271,7 +576,7 @@ func (r *ExtensionRuntime) fileExists(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(err == nil)
 }

-func (r *ExtensionRuntime) fileDelete(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fileDelete(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -300,7 +605,7 @@ func (r *ExtensionRuntime) fileDelete(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) fileRead(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fileRead(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -331,7 +636,117 @@ func (r *ExtensionRuntime) fileRead(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) fileWrite(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fileReadBytes(call goja.FunctionCall) goja.Value {
+	if len(call.Arguments) < 1 {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   "path is required",
+		})
+	}
+
+	path := call.Arguments[0].String()
+	fullPath, err := r.validatePath(path)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	options := parseRuntimeOptionsArgument(call, 1)
+	offset := runtimeOptionInt64(options, "offset", 0)
+	length := runtimeOptionInt64(options, "length", -1)
+	encoding := runtimeOptionString(options, "encoding", "base64")
+	if offset < 0 {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   "offset must be >= 0",
+		})
+	}
+	file, err := os.Open(fullPath)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+	defer file.Close()
+
+	info, err := file.Stat()
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	size := info.Size()
+	if offset > size {
+		offset = size
+	}
+	if _, err := file.Seek(offset, io.SeekStart); err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("failed to seek file: %v", err),
+		})
+	}
+
+	var data []byte
+	switch {
+	case length == 0:
+		data = []byte{}
+	case length > 0:
+		buf := make([]byte, int(length))
+		n, readErr := file.Read(buf)
+		if readErr != nil && readErr != io.EOF {
+			return r.vm.ToValue(map[string]interface{}{
+				"success": false,
+				"error":   fmt.Sprintf("failed to read file: %v", readErr),
+			})
+		}
+		data = buf[:n]
+	default:
+		data, err = io.ReadAll(file)
+		if err != nil {
+			return r.vm.ToValue(map[string]interface{}{
+				"success": false,
+				"error":   fmt.Sprintf("failed to read file: %v", err),
+			})
+		}
+	}
+
+	if strings.EqualFold(strings.TrimSpace(encoding), "bytes") ||
+		strings.EqualFold(strings.TrimSpace(encoding), "raw") {
+		// Return raw bytes as an ArrayBuffer to avoid base64 encode/decode of
+		// large payloads under the goja interpreter.
+		return r.vm.ToValue(map[string]interface{}{
+			"success":    true,
+			"data":       r.vm.NewArrayBuffer(data),
+			"bytes_read": len(data),
+			"offset":     offset,
+			"size":       size,
+			"eof":        offset+int64(len(data)) >= size,
+		})
+	}
+
+	encoded, err := encodeRuntimeBytes(data, encoding)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	return r.vm.ToValue(map[string]interface{}{
+		"success":    true,
+		"data":       encoded,
+		"bytes_read": len(data),
+		"offset":     offset,
+		"size":       size,
+		"eof":        offset+int64(len(data)) >= size,
+	})
+}
+func (r *extensionRuntime) fileWrite(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -371,7 +786,108 @@ func (r *ExtensionRuntime) fileWrite(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) fileCopy(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fileWriteBytes(call goja.FunctionCall) goja.Value {
+	if len(call.Arguments) < 2 {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   "path and data are required",
+		})
+	}
+
+	path := call.Arguments[0].String()
+	fullPath, err := r.validatePath(path)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	options := parseRuntimeOptionsArgument(call, 2)
+	appendMode := runtimeOptionBool(options, "append", false)
+	truncate := runtimeOptionBool(options, "truncate", false)
+	hasOffset := runtimeOptionHasKey(options, "offset")
+	offset := runtimeOptionInt64(options, "offset", 0)
+	encoding := runtimeOptionString(options, "encoding", "base64")
+
+	if appendMode && hasOffset {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   "append and offset cannot be used together",
+		})
+	}
+	if offset < 0 {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   "offset must be >= 0",
+		})
+	}
+
+	data, err := decodeRuntimeBytesValue(call.Arguments[1].Export(), encoding)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	dir := filepath.Dir(fullPath)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   fmt.Sprintf("failed to create directory: %v", err),
+		})
+	}
+
+	flags := os.O_CREATE | os.O_WRONLY
+	if appendMode {
+		flags |= os.O_APPEND
+	}
+	if truncate {
+		flags |= os.O_TRUNC
+	}
+
+	file, err := os.OpenFile(fullPath, flags, 0644)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+	defer file.Close()
+
+	if hasOffset && !appendMode {
+		if _, err := file.Seek(offset, io.SeekStart); err != nil {
+			return r.vm.ToValue(map[string]interface{}{
+				"success": false,
+				"error":   fmt.Sprintf("failed to seek file: %v", err),
+			})
+		}
+	}
+
+	written, err := file.Write(data)
+	if err != nil {
+		return r.vm.ToValue(map[string]interface{}{
+			"success": false,
+			"error":   err.Error(),
+		})
+	}
+
+	info, statErr := file.Stat()
+	size := int64(0)
+	if statErr == nil {
+		size = info.Size()
+	}
+
+	return r.vm.ToValue(map[string]interface{}{
+		"success":       true,
+		"path":          fullPath,
+		"bytes_written": written,
+		"size":          size,
+	})
+}
+
+func (r *extensionRuntime) fileCopy(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -444,7 +960,7 @@ func (r *ExtensionRuntime) fileCopy(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) fileMove(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fileMove(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -492,7 +1008,7 @@ func (r *ExtensionRuntime) fileMove(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) fileGetSize(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fileGetSize(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -17,7 +17,25 @@ type HTTPResponse struct {
 	Headers    map[string]string `json:"headers"`
 }

-func (r *ExtensionRuntime) validateDomain(urlStr string) error {
+const maxExtensionHTTPResponseBytes = 16 << 20
+
+func readExtensionHTTPResponseBody(resp *http.Response) ([]byte, error) {
+	body, err := io.ReadAll(
+		io.LimitReader(resp.Body, maxExtensionHTTPResponseBytes+1),
+	)
+	if err != nil {
+		return nil, err
+	}
+	if len(body) > maxExtensionHTTPResponseBytes {
+		return nil, fmt.Errorf(
+			"response body exceeds %d byte limit; use file.download for large media",
+			maxExtensionHTTPResponseBytes,
+		)
+	}
+	return body, nil
+}
+
+func (r *extensionRuntime) validateDomain(urlStr string) error {
 	parsed, err := url.Parse(urlStr)
 	if err != nil {
 		return fmt.Errorf("invalid URL: %w", err)
@@ -26,7 +44,8 @@ func (r *ExtensionRuntime) validateDomain(urlStr string) error {
 	if parsed.Scheme == "" {
 		return fmt.Errorf("invalid URL: scheme is required")
 	}
-	if parsed.Scheme != "https" {
+	if parsed.Scheme != "https" &&
+		!(parsed.Scheme == "http" && r.manifest.Permissions.AllowHTTP) {
 		return fmt.Errorf("network access denied: only https is allowed")
 	}
 	if parsed.User != nil {
@@ -49,7 +68,7 @@ func (r *ExtensionRuntime) validateDomain(urlStr string) error {
 	return nil
 }

-func (r *ExtensionRuntime) httpGet(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpGet(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": "URL is required",
@@ -81,6 +100,7 @@ func (r *ExtensionRuntime) httpGet(call goja.FunctionCall) goja.Value {
 			"error": err.Error(),
 		})
 	}
+	req = r.bindDownloadCancelContext(req)

 	for k, v := range headers {
 		req.Header.Set(k, v)
@@ -98,7 +118,7 @@ func (r *ExtensionRuntime) httpGet(call goja.FunctionCall) goja.Value {
 	}
 	defer resp.Body.Close()

-	body, err := io.ReadAll(resp.Body)
+	body, err := readExtensionHTTPResponseBody(resp)
 	if err != nil {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": err.Error(),
@@ -118,12 +138,13 @@ func (r *ExtensionRuntime) httpGet(call goja.FunctionCall) goja.Value {
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})
 }

-func (r *ExtensionRuntime) httpPost(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpPost(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": "URL is required",
@@ -174,6 +195,7 @@ func (r *ExtensionRuntime) httpPost(call goja.FunctionCall) goja.Value {
 			"error": err.Error(),
 		})
 	}
+	req = r.bindDownloadCancelContext(req)

 	for k, v := range headers {
 		req.Header.Set(k, v)
@@ -194,7 +216,7 @@ func (r *ExtensionRuntime) httpPost(call goja.FunctionCall) goja.Value {
 	}
 	defer resp.Body.Close()

-	body, err := io.ReadAll(resp.Body)
+	body, err := readExtensionHTTPResponseBody(resp)
 	if err != nil {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": err.Error(),
@@ -214,12 +236,13 @@ func (r *ExtensionRuntime) httpPost(call goja.FunctionCall) goja.Value {
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})
 }

-func (r *ExtensionRuntime) httpRequest(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpRequest(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": "URL is required",
@@ -282,6 +305,7 @@ func (r *ExtensionRuntime) httpRequest(call goja.FunctionCall) goja.Value {
 			"error": err.Error(),
 		})
 	}
+	req = r.bindDownloadCancelContext(req)

 	for k, v := range headers {
 		req.Header.Set(k, v)
@@ -302,7 +326,7 @@ func (r *ExtensionRuntime) httpRequest(call goja.FunctionCall) goja.Value {
 	}
 	defer resp.Body.Close()

-	body, err := io.ReadAll(resp.Body)
+	body, err := readExtensionHTTPResponseBody(resp)
 	if err != nil {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": err.Error(),
@@ -322,24 +346,25 @@ func (r *ExtensionRuntime) httpRequest(call goja.FunctionCall) goja.Value {
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})
 }

-func (r *ExtensionRuntime) httpPut(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpPut(call goja.FunctionCall) goja.Value {
 	return r.httpMethodShortcut("PUT", call)
 }

-func (r *ExtensionRuntime) httpDelete(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpDelete(call goja.FunctionCall) goja.Value {
 	return r.httpMethodShortcut("DELETE", call)
 }

-func (r *ExtensionRuntime) httpPatch(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpPatch(call goja.FunctionCall) goja.Value {
 	return r.httpMethodShortcut("PATCH", call)
 }

-func (r *ExtensionRuntime) httpMethodShortcut(method string, call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpMethodShortcut(method string, call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": "URL is required",
@@ -407,6 +432,7 @@ func (r *ExtensionRuntime) httpMethodShortcut(method string, call goja.FunctionC
 			"error": err.Error(),
 		})
 	}
+	req = r.bindDownloadCancelContext(req)

 	for k, v := range headers {
 		req.Header.Set(k, v)
@@ -426,7 +452,7 @@ func (r *ExtensionRuntime) httpMethodShortcut(method string, call goja.FunctionC
 	}
 	defer resp.Body.Close()

-	body, err := io.ReadAll(resp.Body)
+	body, err := readExtensionHTTPResponseBody(resp)
 	if err != nil {
 		return r.vm.ToValue(map[string]interface{}{
 			"error": err.Error(),
@@ -446,12 +472,13 @@ func (r *ExtensionRuntime) httpMethodShortcut(method string, call goja.FunctionC
 		"statusCode": resp.StatusCode,
 		"status":     resp.StatusCode,
 		"ok":         resp.StatusCode >= 200 && resp.StatusCode < 300,
+		"url":        resp.Request.URL.String(),
 		"body":       string(body),
 		"headers":    respHeaders,
 	})
 }

-func (r *ExtensionRuntime) httpClearCookies(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) httpClearCookies(call goja.FunctionCall) goja.Value {
 	if jar, ok := r.cookieJar.(*simpleCookieJar); ok {
 		jar.mu.Lock()
 		jar.cookies = make(map[string][]*http.Cookie)
@@ -6,7 +6,7 @@ import (
 	"github.com/dop251/goja"
 )

-func (r *ExtensionRuntime) matchingCompareStrings(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) matchingCompareStrings(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(0.0)
 	}
@@ -22,7 +22,7 @@ func (r *ExtensionRuntime) matchingCompareStrings(call goja.FunctionCall) goja.V
 	return r.vm.ToValue(similarity)
 }

-func (r *ExtensionRuntime) matchingCompareDuration(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) matchingCompareDuration(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(false)
 	}
@@ -43,7 +43,7 @@ func (r *ExtensionRuntime) matchingCompareDuration(call goja.FunctionCall) goja.
 	return r.vm.ToValue(diff <= tolerance)
 }

-func (r *ExtensionRuntime) matchingNormalizeString(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) matchingNormalizeString(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -12,11 +12,7 @@ import (
 	"github.com/dop251/goja"
 )

-// These polyfills make porting browser/Node.js libraries easier
-// without compromising sandbox security.
-
-// Returns a Promise-like object with json(), text() methods.
-func (r *ExtensionRuntime) fetchPolyfill(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) fetchPolyfill(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.createFetchError("URL is required")
 	}
@@ -38,7 +34,6 @@ func (r *ExtensionRuntime) fetchPolyfill(call goja.FunctionCall) goja.Value {
 				method = strings.ToUpper(m)
 			}

-			// Body - support string, object (auto-stringify), or nil
 			if bodyArg, ok := opts["body"]; ok && bodyArg != nil {
 				switch v := bodyArg.(type) {
 				case string:
@@ -74,12 +69,13 @@ func (r *ExtensionRuntime) fetchPolyfill(call goja.FunctionCall) goja.Value {
 	if err != nil {
 		return r.createFetchError(err.Error())
 	}
+	req = r.bindDownloadCancelContext(req)

 	for k, v := range headers {
 		req.Header.Set(k, v)
 	}
 	if req.Header.Get("User-Agent") == "" {
-		req.Header.Set("User-Agent", "SpotiFLAC-Extension/1.0")
+		req.Header.Set("User-Agent", appUserAgent())
 	}
 	if bodyStr != "" && req.Header.Get("Content-Type") == "" {
 		req.Header.Set("Content-Type", "application/json")
@@ -110,7 +106,7 @@ func (r *ExtensionRuntime) fetchPolyfill(call goja.FunctionCall) goja.Value {
 	responseObj.Set("status", resp.StatusCode)
 	responseObj.Set("statusText", http.StatusText(resp.StatusCode))
 	responseObj.Set("headers", respHeaders)
-	responseObj.Set("url", urlStr)
+	responseObj.Set("url", resp.Request.URL.String())

 	bodyString := string(body)

@@ -138,7 +134,7 @@ func (r *ExtensionRuntime) fetchPolyfill(call goja.FunctionCall) goja.Value {
 	return responseObj
 }

-func (r *ExtensionRuntime) createFetchError(message string) goja.Value {
+func (r *extensionRuntime) createFetchError(message string) goja.Value {
 	errorObj := r.vm.NewObject()
 	errorObj.Set("ok", false)
 	errorObj.Set("status", 0)
@@ -153,7 +149,7 @@ func (r *ExtensionRuntime) createFetchError(message string) goja.Value {
 	return errorObj
 }

-func (r *ExtensionRuntime) atobPolyfill(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) atobPolyfill(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -169,7 +165,7 @@ func (r *ExtensionRuntime) atobPolyfill(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(string(decoded))
 }

-func (r *ExtensionRuntime) btoaPolyfill(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) btoaPolyfill(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -177,7 +173,7 @@ func (r *ExtensionRuntime) btoaPolyfill(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(base64.StdEncoding.EncodeToString([]byte(input)))
 }

-func (r *ExtensionRuntime) registerTextEncoderDecoder(vm *goja.Runtime) {
+func (r *extensionRuntime) registerTextEncoderDecoder(vm *goja.Runtime) {
 	vm.Set("TextEncoder", func(call goja.ConstructorCall) *goja.Object {
 		encoder := call.This
 		encoder.Set("encoding", "utf-8")
@@ -197,7 +193,6 @@ func (r *ExtensionRuntime) registerTextEncoderDecoder(vm *goja.Runtime) {
 		})

 		encoder.Set("encodeInto", func(call goja.FunctionCall) goja.Value {
-			// Simplified implementation
 			if len(call.Arguments) < 2 {
 				return vm.ToValue(map[string]interface{}{"read": 0, "written": 0})
 			}
@@ -258,7 +253,7 @@ func (r *ExtensionRuntime) registerTextEncoderDecoder(vm *goja.Runtime) {
 	})
 }

-func (r *ExtensionRuntime) registerURLClass(vm *goja.Runtime) {
+func (r *extensionRuntime) registerURLClass(vm *goja.Runtime) {
 	vm.Set("URL", func(call goja.ConstructorCall) *goja.Object {
 		urlObj := call.This

@@ -422,8 +417,7 @@ func (r *ExtensionRuntime) registerURLClass(vm *goja.Runtime) {
 	})
 }

-// JSON is already built-in to Goja; this ensures a fallback exists.
-func (r *ExtensionRuntime) registerJSONGlobal(vm *goja.Runtime) {
+func (r *extensionRuntime) registerJSONGlobal(vm *goja.Runtime) {
 	jsonScript := `
 		if (typeof JSON === 'undefined') {
 			var JSON = {
@@ -21,7 +21,7 @@ const (
 	storageFlushRetryDelay   = 2 * time.Second
 )

-func (r *ExtensionRuntime) getStoragePath() string {
+func (r *extensionRuntime) getStoragePath() string {
 	return filepath.Join(r.dataDir, "storage.json")
 }

@@ -36,7 +36,7 @@ func cloneInterfaceMap(src map[string]interface{}) map[string]interface{} {
 	return dst
 }

-func (r *ExtensionRuntime) ensureStorageLoaded() error {
+func (r *extensionRuntime) ensureStorageLoaded() error {
 	r.storageMu.RLock()
 	if r.storageLoaded {
 		r.storageMu.RUnlock()
@@ -74,7 +74,7 @@ func (r *ExtensionRuntime) ensureStorageLoaded() error {
 	return nil
 }

-func (r *ExtensionRuntime) loadStorage() (map[string]interface{}, error) {
+func (r *extensionRuntime) loadStorage() (map[string]interface{}, error) {
 	if err := r.ensureStorageLoaded(); err != nil {
 		return nil, err
 	}
@@ -84,7 +84,7 @@ func (r *ExtensionRuntime) loadStorage() (map[string]interface{}, error) {
 	return cloneInterfaceMap(r.storageCache), nil
 }

-func (r *ExtensionRuntime) queueStorageFlushLocked(delay time.Duration) {
+func (r *extensionRuntime) queueStorageFlushLocked(delay time.Duration) {
 	if r.storageClosed {
 		return
 	}
@@ -94,7 +94,7 @@ func (r *ExtensionRuntime) queueStorageFlushLocked(delay time.Duration) {
 	r.storageTimer = time.AfterFunc(delay, r.flushStorageDirtyAsync)
 }

-func (r *ExtensionRuntime) persistStorageSnapshot(storage map[string]interface{}) error {
+func (r *extensionRuntime) persistStorageSnapshot(storage map[string]interface{}) error {
 	data, err := json.Marshal(storage)
 	if err != nil {
 		return err
@@ -106,13 +106,13 @@ func (r *ExtensionRuntime) persistStorageSnapshot(storage map[string]interface{}
 	return os.WriteFile(r.getStoragePath(), data, 0600)
 }

-func (r *ExtensionRuntime) flushStorageDirtyAsync() {
+func (r *extensionRuntime) flushStorageDirtyAsync() {
 	if err := r.flushStorageDirty(); err != nil {
 		GoLog("[Extension:%s] Storage flush error: %v\n", r.extensionID, err)
 	}
 }

-func (r *ExtensionRuntime) flushStorageDirty() error {
+func (r *extensionRuntime) flushStorageDirty() error {
 	r.storageMu.Lock()
 	if r.storageClosed {
 		r.storageTimer = nil
@@ -140,7 +140,7 @@ func (r *ExtensionRuntime) flushStorageDirty() error {
 	return nil
 }

-func (r *ExtensionRuntime) flushStorageNow() error {
+func (r *extensionRuntime) flushStorageNow() error {
 	r.storageMu.Lock()
 	if r.storageTimer != nil {
 		r.storageTimer.Stop()
@@ -157,7 +157,7 @@ func (r *ExtensionRuntime) flushStorageNow() error {
 	return r.persistStorageSnapshot(snapshot)
 }

-func (r *ExtensionRuntime) closeStorageFlusher() {
+func (r *extensionRuntime) closeStorageFlusher() {
 	r.storageMu.Lock()
 	r.storageClosed = true
 	r.storageDirty = false
@@ -168,7 +168,7 @@ func (r *ExtensionRuntime) closeStorageFlusher() {
 	r.storageMu.Unlock()
 }

-func (r *ExtensionRuntime) storageGet(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) storageGet(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return goja.Undefined()
 	}
@@ -193,7 +193,7 @@ func (r *ExtensionRuntime) storageGet(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(value)
 }

-func (r *ExtensionRuntime) storageSet(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) storageSet(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(false)
 	}
@@ -225,7 +225,7 @@ func (r *ExtensionRuntime) storageSet(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(true)
 }

-func (r *ExtensionRuntime) storageRemove(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) storageRemove(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(false)
 	}
@@ -254,15 +254,15 @@ func (r *ExtensionRuntime) storageRemove(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(true)
 }

-func (r *ExtensionRuntime) getCredentialsPath() string {
+func (r *extensionRuntime) getCredentialsPath() string {
 	return filepath.Join(r.dataDir, ".credentials.enc")
 }

-func (r *ExtensionRuntime) getSaltPath() string {
+func (r *extensionRuntime) getSaltPath() string {
 	return filepath.Join(r.dataDir, ".cred_salt")
 }

-func (r *ExtensionRuntime) getOrCreateSalt() ([]byte, error) {
+func (r *extensionRuntime) getOrCreateSalt() ([]byte, error) {
 	saltPath := r.getSaltPath()

 	salt, err := os.ReadFile(saltPath)
@@ -282,7 +282,7 @@ func (r *ExtensionRuntime) getOrCreateSalt() ([]byte, error) {
 	return salt, nil
 }

-func (r *ExtensionRuntime) getEncryptionKey() ([]byte, error) {
+func (r *extensionRuntime) getEncryptionKey() ([]byte, error) {
 	salt, err := r.getOrCreateSalt()
 	if err != nil {
 		return nil, err
@@ -293,7 +293,7 @@ func (r *ExtensionRuntime) getEncryptionKey() ([]byte, error) {
 	return hash[:], nil
 }

-func (r *ExtensionRuntime) ensureCredentialsLoaded() error {
+func (r *extensionRuntime) ensureCredentialsLoaded() error {
 	r.credentialsMu.RLock()
 	if r.credentialsLoaded {
 		r.credentialsMu.RUnlock()
@@ -340,17 +340,7 @@ func (r *ExtensionRuntime) ensureCredentialsLoaded() error {
 	return nil
 }

-func (r *ExtensionRuntime) loadCredentials() (map[string]interface{}, error) {
-	if err := r.ensureCredentialsLoaded(); err != nil {
-		return nil, err
-	}
-
-	r.credentialsMu.RLock()
-	defer r.credentialsMu.RUnlock()
-	return cloneInterfaceMap(r.credentialsCache), nil
-}
-
-func (r *ExtensionRuntime) saveCredentials(creds map[string]interface{}) error {
+func (r *extensionRuntime) saveCredentials(creds map[string]interface{}) error {
 	data, err := json.Marshal(creds)
 	if err != nil {
 		return err
@@ -377,7 +367,7 @@ func (r *ExtensionRuntime) saveCredentials(creds map[string]interface{}) error {
 	return nil
 }

-func (r *ExtensionRuntime) credentialsStore(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) credentialsStore(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -414,7 +404,7 @@ func (r *ExtensionRuntime) credentialsStore(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) credentialsGet(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) credentialsGet(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return goja.Undefined()
 	}
@@ -439,7 +429,7 @@ func (r *ExtensionRuntime) credentialsGet(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(value)
 }

-func (r *ExtensionRuntime) credentialsRemove(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) credentialsRemove(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(false)
 	}
@@ -464,7 +454,7 @@ func (r *ExtensionRuntime) credentialsRemove(call goja.FunctionCall) goja.Value
 	return r.vm.ToValue(true)
 }

-func (r *ExtensionRuntime) credentialsHas(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) credentialsHas(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue(false)
 	}
@@ -11,7 +11,7 @@ import (
 	"github.com/dop251/goja"
 )

-func setStorageValue(t *testing.T, runtime *ExtensionRuntime, key string, value interface{}) {
+func setStorageValue(t *testing.T, runtime *extensionRuntime, key string, value interface{}) {
 	t.Helper()
 	result := runtime.storageSet(goja.FunctionCall{
 		Arguments: []goja.Value{
@@ -39,7 +39,7 @@ func readStorageMap(t *testing.T, storagePath string) map[string]interface{} {
 }

 func TestExtensionRuntimeStorage_DebouncedWriteCompactJSON(t *testing.T) {
-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID: "storage-test",
 		Manifest: &ExtensionManifest{
 			Name: "storage-test",
@@ -47,7 +47,7 @@ func TestExtensionRuntimeStorage_DebouncedWriteCompactJSON(t *testing.T) {
 		DataDir: t.TempDir(),
 	}

-	runtime := NewExtensionRuntime(ext)
+	runtime := newExtensionRuntime(ext)
 	runtime.storageFlushDelay = 25 * time.Millisecond
 	runtime.RegisterAPIs(goja.New())

@@ -86,7 +86,7 @@ func TestExtensionRuntimeStorage_DebouncedWriteCompactJSON(t *testing.T) {
 }

 func TestUnloadExtension_FlushesPendingStorage(t *testing.T) {
-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID: "unload-storage-test",
 		Manifest: &ExtensionManifest{
 			Name: "unload-storage-test",
@@ -95,13 +95,13 @@ func TestUnloadExtension_FlushesPendingStorage(t *testing.T) {
 		VM:      goja.New(),
 	}

-	runtime := NewExtensionRuntime(ext)
+	runtime := newExtensionRuntime(ext)
 	runtime.storageFlushDelay = time.Hour
 	runtime.RegisterAPIs(ext.VM)
 	ext.runtime = runtime

-	manager := &ExtensionManager{
-		extensions: map[string]*LoadedExtension{
+	manager := &extensionManager{
+		extensions: map[string]*loadedExtension{
 			ext.ID: ext,
 		},
 	}
@@ -0,0 +1,747 @@
+package gobackend
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/dop251/goja"
+)
+
+func TestExtensionRuntimeAuthAndPolyfills(t *testing.T) {
+	vm := goja.New()
+	runtime := &extensionRuntime{
+		extensionID: "auth-ext",
+		manifest: &ExtensionManifest{
+			Name:        "auth-ext",
+			Description: "Auth extension",
+			Version:     "1.0.0",
+			Permissions: ExtensionPermissions{
+				Network: []string{"auth.example.com", "token.example.com", "api.example.com"},
+			},
+		},
+		settings: map[string]interface{}{},
+		httpClient: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			switch req.URL.Host {
+			case "token.example.com":
+				return &http.Response{
+					StatusCode: 200,
+					Header:     make(http.Header),
+					Body:       io.NopCloser(strings.NewReader(`{"access_token":"access","refresh_token":"refresh","expires_in":3600}`)),
+					Request:    req,
+				}, nil
+			case "api.example.com":
+				return &http.Response{
+					StatusCode: 200,
+					Header:     http.Header{"X-Test": []string{"yes"}},
+					Body:       io.NopCloser(strings.NewReader(`{"ok":true,"items":[1,2]}`)),
+					Request:    req,
+				}, nil
+			default:
+				return &http.Response{StatusCode: 404, Body: io.NopCloser(strings.NewReader(`{}`)), Request: req}, nil
+			}
+		})},
+		vm: vm,
+	}
+
+	if err := validateExtensionAuthURL("https://user:pass@auth.example.com/login"); err == nil {
+		t.Fatal("expected embedded credential error")
+	}
+	if err := validateExtensionAuthURL("http://auth.example.com/login"); err == nil {
+		t.Fatal("expected non-https auth URL error")
+	}
+	if got := summarizeURLForLog("https://auth.example.com/login?token=secret"); got != "https://auth.example.com/login" {
+		t.Fatalf("summary = %q", got)
+	}
+
+	openResult := runtime.authOpenUrl(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("https://auth.example.com/login"),
+		vm.ToValue("app://callback"),
+	}}).Export().(map[string]interface{})
+	if openResult["success"] != true {
+		t.Fatalf("authOpenUrl = %#v", openResult)
+	}
+	if pending := GetPendingAuthRequest("auth-ext"); pending == nil || pending.AuthURL == "" {
+		t.Fatalf("pending auth = %#v", pending)
+	}
+	if code := runtime.authGetCode(goja.FunctionCall{}); !goja.IsUndefined(code) {
+		t.Fatalf("expected undefined code, got %v", code)
+	}
+	if ok := runtime.authSetCode(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(map[string]interface{}{"code": "abc", "access_token": "access", "refresh_token": "refresh", "expires_in": float64(60)})}}); !ok.ToBoolean() {
+		t.Fatal("authSetCode returned false")
+	}
+	if code := runtime.authGetCode(goja.FunctionCall{}).String(); code != "abc" {
+		t.Fatalf("code = %q", code)
+	}
+	if !runtime.authIsAuthenticated(goja.FunctionCall{}).ToBoolean() {
+		t.Fatal("expected authenticated runtime")
+	}
+	tokens := runtime.authGetTokens(goja.FunctionCall{}).Export().(map[string]interface{})
+	if tokens["access_token"] != "access" {
+		t.Fatalf("tokens = %#v", tokens)
+	}
+
+	pkce := runtime.authGeneratePKCE(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(float64(50))}}).Export().(map[string]interface{})
+	if pkce["method"] != "S256" || pkce["verifier"] == "" || pkce["challenge"] == "" {
+		t.Fatalf("pkce = %#v", pkce)
+	}
+	if current := runtime.authGetPKCE(goja.FunctionCall{}).Export().(map[string]interface{}); current["verifier"] == "" {
+		t.Fatalf("current pkce = %#v", current)
+	}
+	oauthConfig := map[string]interface{}{
+		"authUrl":     "https://auth.example.com/oauth",
+		"clientId":    "client",
+		"redirectUri": "app://callback",
+		"scope":       "read",
+		"extraParams": map[string]interface{}{"prompt": "login"},
+	}
+	oauth := runtime.authStartOAuthWithPKCE(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(oauthConfig)}}).Export().(map[string]interface{})
+	if oauth["success"] != true || !strings.Contains(oauth["authUrl"].(string), "code_challenge") {
+		t.Fatalf("oauth = %#v", oauth)
+	}
+	tokenConfig := map[string]interface{}{
+		"tokenUrl":    "https://token.example.com/token",
+		"clientId":    "client",
+		"redirectUri": "app://callback",
+		"code":        "abc",
+	}
+	token := runtime.authExchangeCodeWithPKCE(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(tokenConfig)}}).Export().(map[string]interface{})
+	if token["success"] != true || token["access_token"] != "access" {
+		t.Fatalf("token = %#v", token)
+	}
+
+	runtime.registerTextEncoderDecoder(vm)
+	runtime.registerURLClass(vm)
+	runtime.registerJSONGlobal(vm)
+	vm.Set("fetch", func(call goja.FunctionCall) goja.Value {
+		return runtime.fetchPolyfill(call)
+	})
+	vm.Set("atob", func(call goja.FunctionCall) goja.Value {
+		return runtime.atobPolyfill(call)
+	})
+	vm.Set("btoa", func(call goja.FunctionCall) goja.Value {
+		return runtime.btoaPolyfill(call)
+	})
+
+	value, err := vm.RunString(`
+		var encoded = btoa("hello");
+		var decoded = atob(encoded);
+		var te = new TextEncoder();
+		var bytes = te.encode("hi");
+		var into = te.encodeInto("hi", []);
+		var td = new TextDecoder();
+		var text = td.decode(bytes);
+		var url = new URL("/path?a=1&a=2#frag", "https://api.example.com/base");
+		var params = new URLSearchParams("?x=1");
+		params.append("x", "2");
+		params.set("y", "3");
+		var response = fetch("https://api.example.com/data", {method: "POST", body: {q: "x"}, headers: {"X-Client": "test"}});
+		JSON.stringify({
+			encoded: encoded,
+			decoded: decoded,
+			text: text,
+			read: into.read,
+			host: url.hostname,
+			first: url.searchParams.get("a"),
+			all: url.searchParams.getAll("a").length,
+			params: params.toString(),
+			ok: response.ok,
+			status: response.status,
+			jsonOk: response.json().ok,
+			bufferLen: response.arrayBuffer().length
+		});
+	`)
+	if err != nil {
+		t.Fatalf("polyfill script: %v", err)
+	}
+	var result map[string]interface{}
+	if err := json.Unmarshal([]byte(value.String()), &result); err != nil {
+		t.Fatalf("decode polyfill result: %v", err)
+	}
+	if result["decoded"] != "hello" || result["host"] != "api.example.com" || result["ok"] != true {
+		t.Fatalf("polyfill result = %#v", result)
+	}
+
+	blocked := runtime.fetchPolyfill(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("https://blocked.example.com")}}).ToObject(vm)
+	if blocked.Get("ok").ToBoolean() {
+		t.Fatal("expected blocked fetch")
+	}
+	runtime.authClear(goja.FunctionCall{})
+	if runtime.authIsAuthenticated(goja.FunctionCall{}).ToBoolean() {
+		t.Fatal("expected auth cleared")
+	}
+}
+
+func TestExtensionStoreSettingsAndRuntimeStorage(t *testing.T) {
+	dir := t.TempDir()
+	store := &extensionStore{
+		registryURL: "https://registry.example.com/registry.json",
+		cacheDir:    dir,
+		cacheTTL:    time.Hour,
+		cache: &storeRegistry{
+			Version:   1,
+			UpdatedAt: "2026-05-04",
+			Extensions: []storeExtension{
+				{
+					ID:               "coverage-ext",
+					Name:             "coverage-ext",
+					DisplayNameAlt:   "Coverage Extension",
+					Version:          "2.0.0",
+					Description:      "Metadata and lyrics provider",
+					DownloadURLAlt:   "https://registry.example.com/coverage.spotiflac-ext",
+					IconURLAlt:       "https://registry.example.com/icon.png",
+					Category:         CategoryMetadata,
+					Tags:             []string{"metadata", "lyrics"},
+					Downloads:        10,
+					UpdatedAt:        "2026-05-04",
+					MinAppVersionAlt: "4.5.0",
+				},
+				{
+					ID:          "utility-ext",
+					Name:        "utility-ext",
+					Version:     "1.0.0",
+					Description: "Utility",
+					DownloadURL: "https://registry.example.com/utility.spotiflac-ext",
+					Category:    CategoryUtility,
+					UpdatedAt:   "2026-05-04",
+				},
+			},
+		},
+		cacheTime: time.Now(),
+	}
+	store.saveDiskCache()
+	loadedStore := &extensionStore{cacheDir: dir}
+	loadedStore.loadDiskCache()
+	if loadedStore.cache == nil || len(loadedStore.cache.Extensions) != 2 {
+		t.Fatalf("loaded cache = %#v", loadedStore.cache)
+	}
+	if got := store.getRegistryURL(); got != "https://registry.example.com/registry.json" {
+		t.Fatalf("registry URL = %q", got)
+	}
+	store.setRegistryURL("https://registry.example.com/new.json")
+	if store.cache != nil {
+		t.Fatal("expected cache reset after registry URL change")
+	}
+	store.cache = loadedStore.cache
+	store.cacheTime = time.Now()
+
+	manager := getExtensionManager()
+	manager.mu.Lock()
+	if manager.extensions == nil {
+		manager.extensions = map[string]*loadedExtension{}
+	}
+	manager.extensions["coverage-ext"] = &loadedExtension{
+		ID: "coverage-ext",
+		Manifest: &ExtensionManifest{
+			Name:        "coverage-ext",
+			DisplayName: "Coverage Extension",
+			Version:     "1.0.0",
+			Description: "Installed",
+			Types:       []ExtensionType{ExtensionTypeMetadataProvider},
+		},
+		Enabled: true,
+	}
+	manager.mu.Unlock()
+	defer func() {
+		manager.mu.Lock()
+		delete(manager.extensions, "coverage-ext")
+		manager.mu.Unlock()
+	}()
+
+	extensions, err := store.getExtensionsWithStatus(false)
+	if err != nil {
+		t.Fatalf("getExtensionsWithStatus: %v", err)
+	}
+	if len(extensions) != 2 || !extensions[0].IsInstalled || !extensions[0].HasUpdate {
+		t.Fatalf("extensions = %#v", extensions)
+	}
+	found, err := store.searchExtensions("lyrics", CategoryMetadata)
+	if err != nil || len(found) != 1 || found[0].ID != "coverage-ext" {
+		t.Fatalf("search = %#v/%v", found, err)
+	}
+	all, err := store.searchExtensions("", "")
+	if err != nil || len(all) != 2 {
+		t.Fatalf("all search = %#v/%v", all, err)
+	}
+	if cats := store.getCategories(); len(cats) != 5 {
+		t.Fatalf("categories = %#v", cats)
+	}
+	if !containsIgnoreCase("Hello Metadata", "metadata") || findSubstring("abcdef", "cd") != 2 || containsStr("abc", "z") {
+		t.Fatal("string helper mismatch")
+	}
+	if err := requireHTTPSURL("http://example.com", "registry"); err == nil {
+		t.Fatal("expected HTTPS validation error")
+	}
+	if _, err := resolveRegistryURL(""); err == nil {
+		t.Fatal("expected empty registry URL error")
+	}
+	if resolved, err := resolveRegistryURL("http://github.com/owner/repo"); err != nil || !strings.Contains(resolved, "raw.githubusercontent.com/owner/repo") {
+		t.Fatalf("resolved registry = %q/%v", resolved, err)
+	}
+	store.clearCache()
+	if store.cache != nil {
+		t.Fatal("expected cleared store cache")
+	}
+
+	settingsStore := &ExtensionSettingsStore{settings: map[string]map[string]interface{}{}}
+	if err := settingsStore.SetDataDir(filepath.Join(dir, "settings")); err != nil {
+		t.Fatalf("SetDataDir: %v", err)
+	}
+	if err := settingsStore.Set("ext", "quality", "lossless"); err != nil {
+		t.Fatalf("settings Set: %v", err)
+	}
+	if value, err := settingsStore.Get("ext", "quality"); err != nil || value != "lossless" {
+		t.Fatalf("settings Get = %#v/%v", value, err)
+	}
+	if _, err := settingsStore.Get("ext", "missing"); err == nil {
+		t.Fatal("expected missing setting error")
+	}
+	if err := settingsStore.SetAll("ext", map[string]interface{}{"a": float64(1), "_secret": "hidden"}); err != nil {
+		t.Fatalf("settings SetAll: %v", err)
+	}
+	if all := settingsStore.GetAll("ext"); all["a"] != float64(1) {
+		t.Fatalf("settings all = %#v", all)
+	}
+	if err := settingsStore.Remove("ext", "a"); err != nil {
+		t.Fatalf("settings Remove: %v", err)
+	}
+	if err := settingsStore.RemoveAll("ext"); err != nil {
+		t.Fatalf("settings RemoveAll: %v", err)
+	}
+	if jsonText, err := settingsStore.GetAllExtensionSettingsJSON(); err != nil || jsonText == "" {
+		t.Fatalf("settings JSON = %q/%v", jsonText, err)
+	}
+	reloaded := &ExtensionSettingsStore{settings: map[string]map[string]interface{}{}}
+	if err := reloaded.SetDataDir(settingsStore.dataDir); err != nil {
+		t.Fatalf("reload settings: %v", err)
+	}
+
+	vm := goja.New()
+	runtime := &extensionRuntime{
+		extensionID:       "storage-ext",
+		dataDir:           filepath.Join(dir, "runtime"),
+		vm:                vm,
+		storageFlushDelay: time.Hour,
+	}
+	if err := os.MkdirAll(runtime.dataDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if got := runtime.storageGet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("missing"), vm.ToValue("fallback")}}).String(); got != "fallback" {
+		t.Fatalf("storage fallback = %q", got)
+	}
+	if ok := runtime.storageSet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("key"), vm.ToValue(map[string]interface{}{"nested": "value"})}}); !ok.ToBoolean() {
+		t.Fatal("storageSet false")
+	}
+	if ok := runtime.storageSet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("key"), vm.ToValue(map[string]interface{}{"nested": "value"})}}); !ok.ToBoolean() {
+		t.Fatal("storageSet equal false")
+	}
+	loaded, err := runtime.loadStorage()
+	if err != nil || loaded["key"] == nil {
+		t.Fatalf("loadStorage = %#v/%v", loaded, err)
+	}
+	if err := runtime.flushStorageNow(); err != nil {
+		t.Fatalf("flushStorageNow: %v", err)
+	}
+	if ok := runtime.storageRemove(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("key")}}); !ok.ToBoolean() {
+		t.Fatal("storageRemove false")
+	}
+	runtime.closeStorageFlusher()
+	if ok := runtime.storageSet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("after_close"), vm.ToValue("x")}}); ok.ToBoolean() {
+		t.Fatal("expected storageSet false after close")
+	}
+
+	credRuntime := &extensionRuntime{
+		extensionID: "cred-ext",
+		dataDir:     filepath.Join(dir, "creds"),
+		vm:          vm,
+	}
+	if err := os.MkdirAll(credRuntime.dataDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if result := credRuntime.credentialsStore(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("token"), vm.ToValue("secret")}}).Export().(map[string]interface{}); result["success"] != true {
+		t.Fatalf("credentialsStore = %#v", result)
+	}
+	if got := credRuntime.credentialsGet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("token")}}).String(); got != "secret" {
+		t.Fatalf("credential = %q", got)
+	}
+	if !credRuntime.credentialsHas(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("token")}}).ToBoolean() {
+		t.Fatal("expected credential")
+	}
+	if ok := credRuntime.credentialsRemove(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("token")}}); !ok.ToBoolean() {
+		t.Fatal("credentialsRemove false")
+	}
+	if credRuntime.credentialsHas(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("token")}}).ToBoolean() {
+		t.Fatal("expected credential removed")
+	}
+	key, err := credRuntime.getEncryptionKey()
+	if err != nil {
+		t.Fatalf("getEncryptionKey: %v", err)
+	}
+	encrypted, err := encryptAES([]byte("plain"), key)
+	if err != nil {
+		t.Fatalf("encryptAES: %v", err)
+	}
+	decrypted, err := decryptAES(encrypted, key)
+	if err != nil || string(decrypted) != "plain" {
+		t.Fatalf("decryptAES = %q/%v", decrypted, err)
+	}
+	if _, err := decryptAES([]byte("short"), key); err == nil {
+		t.Fatal("expected short ciphertext error")
+	}
+}
+
+func TestExtensionRuntimeHTTPMatchingAndMetadataHelpers(t *testing.T) {
+	vm := goja.New()
+	jar, _ := newSimpleCookieJar()
+	runtime := &extensionRuntime{
+		extensionID: "http-ext",
+		manifest: &ExtensionManifest{
+			Name:        "http-ext",
+			Description: "HTTP extension",
+			Version:     "1.0.0",
+			Permissions: ExtensionPermissions{
+				Network: []string{"api.example.com"},
+			},
+		},
+		vm:        vm,
+		cookieJar: jar,
+		httpClient: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			var body []byte
+			if req.Body != nil {
+				body, _ = io.ReadAll(req.Body)
+			}
+			header := make(http.Header)
+			header.Set("X-Method", req.Method)
+			if req.URL.Path == "/huge" {
+				return &http.Response{StatusCode: 200, Header: header, Body: io.NopCloser(io.LimitReader(strings.NewReader(strings.Repeat("x", maxExtensionHTTPResponseBytes+2)), maxExtensionHTTPResponseBytes+2)), Request: req}, nil
+			}
+			return &http.Response{
+				StatusCode: 201,
+				Header:     header,
+				Body:       io.NopCloser(strings.NewReader(req.Method + ":" + string(body))),
+				Request:    req,
+			}, nil
+		})},
+	}
+
+	if err := runtime.validateDomain("https://api.example.com/path"); err != nil {
+		t.Fatalf("validateDomain allowed: %v", err)
+	}
+	for _, rawURL := range []string{"notaurl", "http://api.example.com", "https://user:pass@api.example.com", "https://127.0.0.1/x", "https://blocked.example.com/x"} {
+		if err := runtime.validateDomain(rawURL); err == nil {
+			t.Fatalf("expected domain validation error for %s", rawURL)
+		}
+	}
+	if got := runtime.httpGet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("https://api.example.com/get"), vm.ToValue(map[string]interface{}{"X-Test": "yes"})}}).Export().(map[string]interface{}); got["status"] != 201 || !strings.Contains(got["body"].(string), "GET") {
+		t.Fatalf("httpGet = %#v", got)
+	}
+	if got := runtime.httpPost(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("https://api.example.com/post"), vm.ToValue(map[string]interface{}{"a": "b"})}}).Export().(map[string]interface{}); !strings.Contains(got["body"].(string), "POST") {
+		t.Fatalf("httpPost = %#v", got)
+	}
+	requestOptions := map[string]interface{}{"method": "patch", "body": []interface{}{"x"}, "headers": map[string]interface{}{"X-Req": "1"}}
+	if got := runtime.httpRequest(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("https://api.example.com/request"), vm.ToValue(requestOptions)}}).Export().(map[string]interface{}); !strings.Contains(got["body"].(string), "PATCH") {
+		t.Fatalf("httpRequest = %#v", got)
+	}
+	for _, method := range []struct {
+		name string
+		call func(goja.FunctionCall) goja.Value
+		args []goja.Value
+	}{
+		{name: "PUT", call: runtime.httpPut, args: []goja.Value{vm.ToValue("https://api.example.com/put"), vm.ToValue("body")}},
+		{name: "DELETE", call: runtime.httpDelete, args: []goja.Value{vm.ToValue("https://api.example.com/delete"), vm.ToValue(map[string]interface{}{"X-Delete": "1"})}},
+		{name: "PATCH", call: runtime.httpPatch, args: []goja.Value{vm.ToValue("https://api.example.com/patch"), vm.ToValue(map[string]interface{}{"p": "q"})}},
+	} {
+		if got := method.call(goja.FunctionCall{Arguments: method.args}).Export().(map[string]interface{}); !strings.Contains(got["body"].(string), method.name) {
+			t.Fatalf("%s = %#v", method.name, got)
+		}
+	}
+	if got := runtime.httpGet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("https://api.example.com/huge")}}).Export().(map[string]interface{}); !strings.Contains(got["error"].(string), "exceeds") {
+		t.Fatalf("huge response = %#v", got)
+	}
+	if !runtime.httpClearCookies(goja.FunctionCall{}).ToBoolean() {
+		t.Fatal("expected cookies cleared")
+	}
+
+	if runtime.matchingCompareStrings(goja.FunctionCall{}).ToFloat() != 0 {
+		t.Fatal("missing string compare args should be zero")
+	}
+	if runtime.matchingCompareStrings(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("Song"), vm.ToValue("song")}}).ToFloat() != 1 {
+		t.Fatal("expected exact string similarity")
+	}
+	if runtime.matchingCompareDuration(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(180000), vm.ToValue(182000)}}).ToBoolean() != true {
+		t.Fatal("expected duration match")
+	}
+	if runtime.matchingNormalizeString(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("Song (Remastered) feat. Guest!")}}).String() != "song" {
+		t.Fatalf("normalized = %q", runtime.matchingNormalizeString(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("Song (Remastered) feat. Guest!")}}).String())
+	}
+
+	if formatMusicBrainzGenre([]musicBrainzTag{{Count: 1, Name: "rock"}, {Count: 5, Name: "electronic"}, {Count: 10, Name: "rock"}}) != "Electronic" {
+		t.Fatal("unexpected genre selection")
+	}
+	credits := []musicBrainzArtistCredit{{Name: "A", JoinPhrase: " & "}, {Name: "B"}}
+	if formatMusicBrainzArtistCredit(credits) != "A & B" {
+		t.Fatal("artist credit format mismatch")
+	}
+	releases := []musicBrainzRelease{
+		{Title: "Other", ArtistCredit: []musicBrainzArtistCredit{{Name: "Fallback"}}},
+		{Title: "Album", ArtistCredit: credits},
+	}
+	if selectMusicBrainzAlbumArtist(releases, "Album") != "A & B" || selectMusicBrainzAlbumArtist(releases, "") != "Fallback" {
+		t.Fatal("album artist selection mismatch")
+	}
+}
+
+func TestExtensionRuntimeFileAPIs(t *testing.T) {
+	vm := goja.New()
+	dir := t.TempDir()
+	SetAllowedDownloadDirs(nil)
+	defer SetAllowedDownloadDirs(nil)
+
+	fileBody := "chunk"
+	runtime := &extensionRuntime{
+		extensionID: "file-ext",
+		manifest: &ExtensionManifest{
+			Name:        "file-ext",
+			Description: "File extension",
+			Version:     "1.0.0",
+			Permissions: ExtensionPermissions{
+				File:    true,
+				Network: []string{"files.example.com"},
+			},
+		},
+		dataDir: dir,
+		vm:      vm,
+		httpClient: &http.Client{Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			if req.Header.Get("Range") == "" {
+				body := "downloaded"
+				return &http.Response{
+					StatusCode:    200,
+					Header:        make(http.Header),
+					Body:          io.NopCloser(strings.NewReader(body)),
+					ContentLength: int64(len(body)),
+					Request:       req,
+				}, nil
+			}
+			rangeHeader := req.Header.Get("Range")
+			start, end := 0, len(fileBody)-1
+			if _, err := fmt.Sscanf(rangeHeader, "bytes=%d-%d", &start, &end); err != nil {
+				start, end = 0, 1
+			}
+			if start < 0 {
+				start = 0
+			}
+			if end >= len(fileBody) {
+				end = len(fileBody) - 1
+			}
+			if start > len(fileBody) {
+				start = len(fileBody)
+			}
+			body := fileBody[start : end+1]
+			header := http.Header{"Content-Range": []string{fmt.Sprintf("bytes %d-%d/%d", start, end, len(fileBody))}}
+			return &http.Response{StatusCode: 206, Header: header, Body: io.NopCloser(strings.NewReader(body)), Request: req}, nil
+		})},
+	}
+	runtime.downloadClient = runtime.httpClient
+
+	if _, err := (&extensionRuntime{manifest: &ExtensionManifest{}}).validatePath("x"); err == nil {
+		t.Fatal("expected file permission error")
+	}
+	if _, err := runtime.validatePath("../escape.txt"); err == nil {
+		t.Fatal("expected sandbox escape error")
+	}
+	AddAllowedDownloadDir(dir)
+	absolutePath := filepath.Join(dir, "allowed.txt")
+	if got, err := runtime.validatePath(absolutePath); err != nil || got != absolutePath {
+		t.Fatalf("absolute validatePath = %q/%v", got, err)
+	}
+
+	write := runtime.fileWrite(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("nested/a.txt"), vm.ToValue("hello")}}).Export().(map[string]interface{})
+	if write["success"] != true {
+		t.Fatalf("fileWrite = %#v", write)
+	}
+	if !runtime.fileExists(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("nested/a.txt")}}).ToBoolean() {
+		t.Fatal("expected written file to exist")
+	}
+	read := runtime.fileRead(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("nested/a.txt")}}).Export().(map[string]interface{})
+	if read["data"] != "hello" {
+		t.Fatalf("fileRead = %#v", read)
+	}
+
+	writeBytes := runtime.fileWriteBytes(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("nested/bytes.bin"),
+		vm.ToValue("4869"),
+		vm.ToValue(map[string]interface{}{"encoding": "hex", "truncate": true}),
+	}}).Export().(map[string]interface{})
+	if writeBytes["success"] != true {
+		t.Fatalf("fileWriteBytes = %#v", writeBytes)
+	}
+	appendBytes := runtime.fileWriteBytes(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("nested/bytes.bin"),
+		vm.ToValue([]interface{}{float64('!')}),
+		vm.ToValue(map[string]interface{}{"append": true}),
+	}}).Export().(map[string]interface{})
+	if appendBytes["success"] != true {
+		t.Fatalf("append fileWriteBytes = %#v", appendBytes)
+	}
+	readBytes := runtime.fileReadBytes(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("nested/bytes.bin"),
+		vm.ToValue(map[string]interface{}{"encoding": "text", "offset": float64(1), "length": float64(2)}),
+	}}).Export().(map[string]interface{})
+	if readBytes["data"] != "i!" || readBytes["bytes_read"] != 2 {
+		t.Fatalf("fileReadBytes = %#v", readBytes)
+	}
+	if bad := runtime.fileWriteBytes(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("nested/bad.bin"),
+		vm.ToValue("x"),
+		vm.ToValue(map[string]interface{}{"append": true, "offset": float64(1)}),
+	}}).Export().(map[string]interface{}); bad["success"] != false {
+		t.Fatalf("expected append+offset failure, got %#v", bad)
+	}
+	if bad := runtime.fileReadBytes(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("nested/bytes.bin"),
+		vm.ToValue(map[string]interface{}{"encoding": "bad"}),
+	}}).Export().(map[string]interface{}); bad["success"] != false {
+		t.Fatalf("expected bad encoding failure, got %#v", bad)
+	}
+
+	copyResult := runtime.fileCopy(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("nested/bytes.bin"), vm.ToValue("nested/copy.bin")}}).Export().(map[string]interface{})
+	if copyResult["success"] != true {
+		t.Fatalf("fileCopy = %#v", copyResult)
+	}
+	moveResult := runtime.fileMove(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("nested/copy.bin"), vm.ToValue("nested/moved.bin")}}).Export().(map[string]interface{})
+	if moveResult["success"] != true {
+		t.Fatalf("fileMove = %#v", moveResult)
+	}
+	sizeResult := runtime.fileGetSize(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("nested/moved.bin")}}).Export().(map[string]interface{})
+	if sizeResult["success"] != true || sizeResult["size"] != int64(3) {
+		t.Fatalf("fileGetSize = %#v", sizeResult)
+	}
+	deleteResult := runtime.fileDelete(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("nested/moved.bin")}}).Export().(map[string]interface{})
+	if deleteResult["success"] != true {
+		t.Fatalf("fileDelete = %#v", deleteResult)
+	}
+
+	download := runtime.fileDownload(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("https://files.example.com/file"),
+		vm.ToValue("downloads/file.bin"),
+	}}).Export().(map[string]interface{})
+	if download["success"] != true {
+		t.Fatalf("fileDownload = %#v", download)
+	}
+	if data, err := os.ReadFile(filepath.Join(dir, "downloads/file.bin")); err != nil || string(data) != "downloaded" {
+		t.Fatalf("downloaded data = %q/%v", data, err)
+	}
+
+	chunked := runtime.fileDownload(goja.FunctionCall{Arguments: []goja.Value{
+		vm.ToValue("https://files.example.com/chunk"),
+		vm.ToValue("downloads/chunk.bin"),
+		vm.ToValue(map[string]interface{}{"chunked": float64(2), "headers": map[string]interface{}{"X-Test": "yes"}}),
+	}}).Export().(map[string]interface{})
+	if chunked["success"] != true {
+		t.Fatalf("chunked fileDownload = %#v", chunked)
+	}
+	if data, err := os.ReadFile(filepath.Join(dir, "downloads/chunk.bin")); err != nil || string(data) != fileBody {
+		t.Fatalf("chunked data = %q/%v", data, err)
+	}
+
+	if missing := runtime.fileDownload(goja.FunctionCall{}).Export().(map[string]interface{}); missing["success"] != false {
+		t.Fatalf("expected missing download args error, got %#v", missing)
+	}
+}
+
+func TestExtensionRuntimeUtilityAPIs(t *testing.T) {
+	vm := goja.New()
+	runtime := &extensionRuntime{extensionID: "utils-ext", vm: vm}
+
+	if runtime.sha256Hash(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("abc")}}).String() == "" {
+		t.Fatal("expected sha256")
+	}
+	if runtime.hmacSHA256(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("msg"), vm.ToValue("key")}}).String() == "" {
+		t.Fatal("expected hmac sha256")
+	}
+	if runtime.hmacSHA256Base64(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("msg"), vm.ToValue("key")}}).String() == "" {
+		t.Fatal("expected hmac sha256 base64")
+	}
+	if value := runtime.hmacSHA1(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue([]interface{}{float64(1), float64(2)}), vm.ToValue([]interface{}{float64(3)})}}); len(value.Export().([]interface{})) == 0 {
+		t.Fatal("expected hmac sha1 bytes")
+	}
+	if !goja.IsUndefined(runtime.parseJSON(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(`{bad`)}})) {
+		t.Fatal("expected invalid JSON to return undefined")
+	}
+	parsed := runtime.parseJSON(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(`{"ok":true}`)}}).Export().(map[string]interface{})
+	if parsed["ok"] != true {
+		t.Fatalf("parseJSON = %#v", parsed)
+	}
+	if text := runtime.stringifyJSON(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(map[string]interface{}{"ok": true})}}).String(); !strings.Contains(text, "ok") {
+		t.Fatalf("stringifyJSON = %q", text)
+	}
+	encrypted := runtime.cryptoEncrypt(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("plain"), vm.ToValue("secret")}}).Export().(map[string]interface{})
+	if encrypted["success"] != true || encrypted["data"] == "" {
+		t.Fatalf("cryptoEncrypt = %#v", encrypted)
+	}
+	decrypted := runtime.cryptoDecrypt(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(encrypted["data"]), vm.ToValue("secret")}}).Export().(map[string]interface{})
+	if decrypted["success"] != true || decrypted["data"] != "plain" {
+		t.Fatalf("cryptoDecrypt = %#v", decrypted)
+	}
+	if bad := runtime.cryptoDecrypt(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("bad"), vm.ToValue("secret")}}).Export().(map[string]interface{}); bad["success"] != false {
+		t.Fatalf("expected bad decrypt failure, got %#v", bad)
+	}
+	key := runtime.cryptoGenerateKey(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(float64(8))}}).Export().(map[string]interface{})
+	if key["success"] != true || key["key"] == "" || key["hex"] == "" {
+		t.Fatalf("cryptoGenerateKey = %#v", key)
+	}
+	if runtime.randomUserAgent(goja.FunctionCall{}).String() == "" || runtime.appUserAgent(goja.FunctionCall{}).String() == "" {
+		t.Fatal("expected user agents")
+	}
+	SetAppVersion("9.9.9")
+	if runtime.appVersion(goja.FunctionCall{}).String() != "9.9.9" {
+		t.Fatal("appVersion mismatch")
+	}
+	if !runtime.sleep(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(float64(0))}}).ToBoolean() {
+		t.Fatal("zero sleep should succeed")
+	}
+
+	itemID := "utils-item"
+	runtime.setActiveDownloadItemID(itemID)
+	initDownloadCancel(itemID)
+	if runtime.isDownloadCancelled(goja.FunctionCall{}).ToBoolean() {
+		t.Fatal("item should not be cancelled yet")
+	}
+	runtime.setDownloadStatus(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue(itemProgressStatusDownloading)}})
+	cancelDownload(itemID)
+	if !runtime.isDownloadCancelled(goja.FunctionCall{}).ToBoolean() {
+		t.Fatal("item should be cancelled")
+	}
+	clearDownloadCancel(itemID)
+	runtime.clearActiveDownloadItemID()
+
+	requestID := "utils-request"
+	runtime.setActiveRequestID(requestID)
+	initExtensionRequestCancel(requestID)
+	if runtime.isRequestCancelled(goja.FunctionCall{}).ToBoolean() {
+		t.Fatal("request should not be cancelled yet")
+	}
+	cancelExtensionRequest(requestID)
+	if !runtime.isRequestCancelled(goja.FunctionCall{}).ToBoolean() {
+		t.Fatal("request should be cancelled")
+	}
+	clearExtensionRequestCancel(requestID)
+	runtime.clearActiveRequestID()
+
+	if msg := runtime.formatLogArgs([]goja.Value{vm.ToValue("a"), vm.ToValue(1)}); msg != "a 1" {
+		t.Fatalf("formatLogArgs = %q", msg)
+	}
+	runtime.logDebug(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("debug")}})
+	runtime.logInfo(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("info")}})
+	runtime.logWarn(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("warn")}})
+	runtime.logError(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("error")}})
+	if clean := runtime.sanitizeFilenameWrapper(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("A/B?")}}).String(); strings.ContainsAny(clean, "/?") {
+		t.Fatalf("sanitize wrapper = %q", clean)
+	}
+}
@@ -16,7 +16,7 @@ import (
 	"github.com/dop251/goja"
 )

-func (r *ExtensionRuntime) base64Encode(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) base64Encode(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -24,7 +24,7 @@ func (r *ExtensionRuntime) base64Encode(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(base64.StdEncoding.EncodeToString([]byte(input)))
 }

-func (r *ExtensionRuntime) base64Decode(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) base64Decode(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -36,7 +36,7 @@ func (r *ExtensionRuntime) base64Decode(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(string(decoded))
 }

-func (r *ExtensionRuntime) md5Hash(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) md5Hash(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -45,7 +45,7 @@ func (r *ExtensionRuntime) md5Hash(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(hex.EncodeToString(hash[:]))
 }

-func (r *ExtensionRuntime) sha256Hash(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) sha256Hash(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -54,7 +54,7 @@ func (r *ExtensionRuntime) sha256Hash(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(hex.EncodeToString(hash[:]))
 }

-func (r *ExtensionRuntime) hmacSHA256(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) hmacSHA256(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue("")
 	}
@@ -66,7 +66,7 @@ func (r *ExtensionRuntime) hmacSHA256(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(hex.EncodeToString(mac.Sum(nil)))
 }

-func (r *ExtensionRuntime) hmacSHA256Base64(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) hmacSHA256Base64(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue("")
 	}
@@ -78,7 +78,7 @@ func (r *ExtensionRuntime) hmacSHA256Base64(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(base64.StdEncoding.EncodeToString(mac.Sum(nil)))
 }

-func (r *ExtensionRuntime) hmacSHA1(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) hmacSHA1(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue([]byte{})
 	}
@@ -130,7 +130,7 @@ func (r *ExtensionRuntime) hmacSHA1(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(jsArray)
 }

-func (r *ExtensionRuntime) parseJSON(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) parseJSON(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return goja.Undefined()
 	}
@@ -145,7 +145,7 @@ func (r *ExtensionRuntime) parseJSON(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(result)
 }

-func (r *ExtensionRuntime) stringifyJSON(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) stringifyJSON(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -160,7 +160,7 @@ func (r *ExtensionRuntime) stringifyJSON(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(string(data))
 }

-func (r *ExtensionRuntime) cryptoEncrypt(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) cryptoEncrypt(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -187,7 +187,7 @@ func (r *ExtensionRuntime) cryptoEncrypt(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) cryptoDecrypt(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) cryptoDecrypt(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 2 {
 		return r.vm.ToValue(map[string]interface{}{
 			"success": false,
@@ -222,7 +222,7 @@ func (r *ExtensionRuntime) cryptoDecrypt(call goja.FunctionCall) goja.Value {
 	})
 }

-func (r *ExtensionRuntime) cryptoGenerateKey(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) cryptoGenerateKey(call goja.FunctionCall) goja.Value {
 	length := 32
 	if len(call.Arguments) > 0 && !goja.IsUndefined(call.Arguments[0]) {
 		if l, ok := call.Arguments[0].Export().(float64); ok {
@@ -245,35 +245,125 @@ func (r *ExtensionRuntime) cryptoGenerateKey(call goja.FunctionCall) goja.Value
 	})
 }

-func (r *ExtensionRuntime) randomUserAgent(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) randomUserAgent(call goja.FunctionCall) goja.Value {
 	return r.vm.ToValue(getRandomUserAgent())
 }

-func (r *ExtensionRuntime) logDebug(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) appVersion(call goja.FunctionCall) goja.Value {
+	return r.vm.ToValue(GetAppVersion())
+}
+
+func (r *extensionRuntime) appUserAgent(call goja.FunctionCall) goja.Value {
+	return r.vm.ToValue(appUserAgent())
+}
+
+func (r *extensionRuntime) sleep(call goja.FunctionCall) goja.Value {
+	if len(call.Arguments) < 1 {
+		return r.vm.ToValue(true)
+	}
+
+	sleepMs := 0
+	switch value := call.Arguments[0].Export().(type) {
+	case int64:
+		sleepMs = int(value)
+	case int32:
+		sleepMs = int(value)
+	case int:
+		sleepMs = value
+	case float64:
+		sleepMs = int(value)
+	default:
+		sleepMs = 0
+	}
+
+	if sleepMs <= 0 {
+		return r.vm.ToValue(true)
+	}
+	if sleepMs > 5*60*1000 {
+		sleepMs = 5 * 60 * 1000
+	}
+
+	itemID := r.getActiveDownloadItemID()
+	deadline := time.Now().Add(time.Duration(sleepMs) * time.Millisecond)
+
+	for {
+		if itemID != "" && isDownloadCancelled(itemID) {
+			return r.vm.ToValue(false)
+		}
+
+		remaining := time.Until(deadline)
+		if remaining <= 0 {
+			return r.vm.ToValue(true)
+		}
+
+		step := 100 * time.Millisecond
+		if remaining < step {
+			step = remaining
+		}
+		time.Sleep(step)
+	}
+}
+
+func (r *extensionRuntime) isDownloadCancelled(call goja.FunctionCall) goja.Value {
+	itemID := r.getActiveDownloadItemID()
+	if itemID == "" {
+		return r.vm.ToValue(false)
+	}
+	return r.vm.ToValue(isDownloadCancelled(itemID))
+}
+
+func (r *extensionRuntime) isRequestCancelled(call goja.FunctionCall) goja.Value {
+	requestID := r.getActiveRequestID()
+	if requestID == "" {
+		return r.vm.ToValue(false)
+	}
+	return r.vm.ToValue(isExtensionRequestCancelled(requestID))
+}
+
+func (r *extensionRuntime) setDownloadStatus(call goja.FunctionCall) goja.Value {
+	itemID := r.getActiveDownloadItemID()
+	if itemID == "" || len(call.Arguments) < 1 {
+		return goja.Undefined()
+	}
+
+	status := strings.ToLower(strings.TrimSpace(call.Arguments[0].String()))
+	switch status {
+	case itemProgressStatusPreparing:
+		SetItemPreparing(itemID)
+	case itemProgressStatusDownloading:
+		SetItemDownloading(itemID)
+	case itemProgressStatusFinalizing:
+		SetItemFinalizing(itemID)
+	}
+
+	return goja.Undefined()
+}
+
+func (r *extensionRuntime) logDebug(call goja.FunctionCall) goja.Value {
 	msg := r.formatLogArgs(call.Arguments)
 	GoLog("[Extension:%s:DEBUG] %s\n", r.extensionID, msg)
 	return goja.Undefined()
 }

-func (r *ExtensionRuntime) logInfo(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) logInfo(call goja.FunctionCall) goja.Value {
 	msg := r.formatLogArgs(call.Arguments)
 	GoLog("[Extension:%s:INFO] %s\n", r.extensionID, msg)
 	return goja.Undefined()
 }

-func (r *ExtensionRuntime) logWarn(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) logWarn(call goja.FunctionCall) goja.Value {
 	msg := r.formatLogArgs(call.Arguments)
 	GoLog("[Extension:%s:WARN] %s\n", r.extensionID, msg)
 	return goja.Undefined()
 }

-func (r *ExtensionRuntime) logError(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) logError(call goja.FunctionCall) goja.Value {
 	msg := r.formatLogArgs(call.Arguments)
 	GoLog("[Extension:%s:ERROR] %s\n", r.extensionID, msg)
 	return goja.Undefined()
 }

-func (r *ExtensionRuntime) formatLogArgs(args []goja.Value) string {
+func (r *extensionRuntime) formatLogArgs(args []goja.Value) string {
 	parts := make([]string, len(args))
 	for i, arg := range args {
 		parts[i] = fmt.Sprintf("%v", arg.Export())
@@ -281,7 +371,7 @@ func (r *ExtensionRuntime) formatLogArgs(args []goja.Value) string {
 	return strings.Join(parts, " ")
 }

-func (r *ExtensionRuntime) sanitizeFilenameWrapper(call goja.FunctionCall) goja.Value {
+func (r *extensionRuntime) sanitizeFilenameWrapper(call goja.FunctionCall) goja.Value {
 	if len(call.Arguments) < 1 {
 		return r.vm.ToValue("")
 	}
@@ -289,7 +379,7 @@ func (r *ExtensionRuntime) sanitizeFilenameWrapper(call goja.FunctionCall) goja.
 	return r.vm.ToValue(sanitizeFilename(input))
 }

-func (r *ExtensionRuntime) RegisterGoBackendAPIs(vm *goja.Runtime) {
+func (r *extensionRuntime) RegisterGoBackendAPIs(vm *goja.Runtime) {
 	gobackendObj := vm.Get("gobackend")
 	if gobackendObj == nil || goja.IsUndefined(gobackendObj) {
 		gobackendObj = vm.NewObject()
@@ -324,6 +414,83 @@ func (r *ExtensionRuntime) RegisterGoBackendAPIs(vm *goja.Runtime) {
 			"bitDepth":     quality.BitDepth,
 			"sampleRate":   quality.SampleRate,
 			"totalSamples": quality.TotalSamples,
+			"duration":     quality.Duration,
+			"codec":        quality.Codec,
+		})
+	})
+
+	obj.Set("getLyricsLRC", func(call goja.FunctionCall) goja.Value {
+		if len(call.Arguments) < 3 {
+			return vm.ToValue(map[string]interface{}{
+				"error": "spotifyID, trackName, and artistName are required",
+			})
+		}
+
+		spotifyID := strings.TrimSpace(call.Arguments[0].String())
+		trackName := strings.TrimSpace(call.Arguments[1].String())
+		artistName := strings.TrimSpace(call.Arguments[2].String())
+		filePath := ""
+		if len(call.Arguments) > 3 && !goja.IsUndefined(call.Arguments[3]) && !goja.IsNull(call.Arguments[3]) {
+			filePath = strings.TrimSpace(call.Arguments[3].String())
+		}
+		var durationMs int64
+		if len(call.Arguments) > 4 && !goja.IsUndefined(call.Arguments[4]) && !goja.IsNull(call.Arguments[4]) {
+			durationMs = call.Arguments[4].ToInteger()
+		}
+
+		lyrics, err := GetLyricsLRC(spotifyID, trackName, artistName, filePath, durationMs)
+		if err != nil {
+			return vm.ToValue(map[string]interface{}{
+				"error": err.Error(),
+			})
+		}
+
+		return vm.ToValue(map[string]interface{}{
+			"lyrics": lyrics,
+		})
+	})
+
+	obj.Set("checkISRCExists", func(call goja.FunctionCall) goja.Value {
+		if len(call.Arguments) < 2 {
+			return vm.ToValue(map[string]interface{}{
+				"error": "outputDir and isrc are required",
+			})
+		}
+
+		outputDir := strings.TrimSpace(call.Arguments[0].String())
+		isrc := strings.TrimSpace(call.Arguments[1].String())
+		if outputDir == "" || isrc == "" {
+			return vm.ToValue(map[string]interface{}{
+				"error": "outputDir and isrc are required",
+			})
+		}
+
+		filePath, exists := checkISRCExistsInternal(outputDir, isrc)
+		return vm.ToValue(map[string]interface{}{
+			"exists":   exists,
+			"filePath": filePath,
+		})
+	})
+
+	obj.Set("addToISRCIndex", func(call goja.FunctionCall) goja.Value {
+		if len(call.Arguments) < 3 {
+			return vm.ToValue(map[string]interface{}{
+				"error": "outputDir, isrc, and filePath are required",
+			})
+		}
+
+		outputDir := strings.TrimSpace(call.Arguments[0].String())
+		isrc := strings.TrimSpace(call.Arguments[1].String())
+		filePath := strings.TrimSpace(call.Arguments[2].String())
+		if outputDir == "" || isrc == "" || filePath == "" {
+			return vm.ToValue(map[string]interface{}{
+				"error": "outputDir, isrc, and filePath are required",
+			})
+		}
+
+		AddToISRCIndex(outputDir, isrc, filePath)
+		return vm.ToValue(map[string]interface{}{
+			"success": true,
 		})
 	})

@@ -21,12 +21,11 @@ const (
 	CategoryIntegration = "integration"
 )

-type StoreExtension struct {
+type storeExtension struct {
 	ID               string   `json:"id"`
 	Name             string   `json:"name"`
 	DisplayName      string   `json:"display_name,omitempty"`
 	Version          string   `json:"version"`
-	Author           string   `json:"author"`
 	Description      string   `json:"description"`
 	DownloadURL      string   `json:"download_url,omitempty"`
 	IconURL          string   `json:"icon_url,omitempty"`
@@ -41,7 +40,7 @@ type StoreExtension struct {
 	MinAppVersionAlt string   `json:"minAppVersion,omitempty"`
 }

-func (e *StoreExtension) getDisplayName() string {
+func (e *storeExtension) getDisplayName() string {
 	if e.DisplayName != "" {
 		return e.DisplayName
 	}
@@ -51,39 +50,38 @@ func (e *StoreExtension) getDisplayName() string {
 	return e.Name
 }

-func (e *StoreExtension) getDownloadURL() string {
+func (e *storeExtension) getDownloadURL() string {
 	if e.DownloadURL != "" {
 		return e.DownloadURL
 	}
 	return e.DownloadURLAlt
 }

-func (e *StoreExtension) getIconURL() string {
+func (e *storeExtension) getIconURL() string {
 	if e.IconURL != "" {
 		return e.IconURL
 	}
 	return e.IconURLAlt
 }

-func (e *StoreExtension) getMinAppVersion() string {
+func (e *storeExtension) getMinAppVersion() string {
 	if e.MinAppVersion != "" {
 		return e.MinAppVersion
 	}
 	return e.MinAppVersionAlt
 }

-type StoreRegistry struct {
+type storeRegistry struct {
 	Version    int              `json:"version"`
 	UpdatedAt  string           `json:"updated_at"`
-	Extensions []StoreExtension `json:"extensions"`
+	Extensions []storeExtension `json:"extensions"`
 }

-type StoreExtensionResponse struct {
+type storeExtensionResponse struct {
 	ID               string   `json:"id"`
 	Name             string   `json:"name"`
 	DisplayName      string   `json:"display_name"`
 	Version          string   `json:"version"`
-	Author           string   `json:"author"`
 	Description      string   `json:"description"`
 	DownloadURL      string   `json:"download_url"`
 	IconURL          string   `json:"icon_url,omitempty"`
@@ -97,36 +95,40 @@ type StoreExtensionResponse struct {
 	HasUpdate        bool     `json:"has_update"`
 }

-func (e *StoreExtension) ToResponse() StoreExtensionResponse {
-	return StoreExtensionResponse{
+func (e *storeExtension) toResponse() storeExtensionResponse {
+	resp := storeExtensionResponse{
 		ID:            e.ID,
 		Name:          e.Name,
 		DisplayName:   e.getDisplayName(),
 		Version:       e.Version,
-		Author:        e.Author,
 		Description:   e.Description,
 		DownloadURL:   e.getDownloadURL(),
 		IconURL:       e.getIconURL(),
 		Category:      e.Category,
-		Tags:          e.Tags,
 		Downloads:     e.Downloads,
 		UpdatedAt:     e.UpdatedAt,
 		MinAppVersion: e.getMinAppVersion(),
 	}
+
+	if len(e.Tags) > 0 {
+		resp.Tags = append([]string(nil), e.Tags...)
+	}
+
+	return resp
 }

-type ExtensionStore struct {
+type extensionStore struct {
 	registryURL string
 	cacheDir    string
-	cache       *StoreRegistry
+	cache       *storeRegistry
 	cacheMu     sync.RWMutex
 	cacheTime   time.Time
 	cacheTTL    time.Duration
 }

 var (
-	extensionStore   *ExtensionStore
-	extensionStoreMu sync.Mutex
+	globalExtensionStore *extensionStore
+	extensionStoreMu     sync.Mutex
 )

 const (
@@ -134,24 +136,22 @@ const (
 	cacheFileName = "store_cache.json"
 )

-func InitExtensionStore(cacheDir string) *ExtensionStore {
+func initExtensionStore(cacheDir string) *extensionStore {
 	extensionStoreMu.Lock()
 	defer extensionStoreMu.Unlock()

-	if extensionStore == nil {
-		extensionStore = &ExtensionStore{
-			registryURL: "", // No default - user must provide a registry URL
+	if globalExtensionStore == nil {
+		globalExtensionStore = &extensionStore{
+			registryURL: "",
 			cacheDir:    cacheDir,
 			cacheTTL:    cacheTTL,
 		}
-		extensionStore.loadDiskCache()
+		globalExtensionStore.loadDiskCache()
 	}
-	return extensionStore
+	return globalExtensionStore
 }

-// SetRegistryURL updates the registry URL and clears the in-memory cache
-// so the next fetch will use the new URL. Disk cache is also cleared.
-func (s *ExtensionStore) SetRegistryURL(registryURL string) {
+func (s *extensionStore) setRegistryURL(registryURL string) {
 	s.cacheMu.Lock()
 	defer s.cacheMu.Unlock()

@@ -163,7 +163,6 @@ func (s *ExtensionStore) SetRegistryURL(registryURL string) {
 	s.cache = nil
 	s.cacheTime = time.Time{}

-	// Clear disk cache since it's from a different registry
 	if s.cacheDir != "" {
 		cachePath := filepath.Join(s.cacheDir, cacheFileName)
 		os.Remove(cachePath)
@@ -172,20 +171,19 @@ func (s *ExtensionStore) SetRegistryURL(registryURL string) {
 	LogInfo("ExtensionStore", "Registry URL updated to: %s", registryURL)
 }

-// GetRegistryURL returns the currently configured registry URL.
-func (s *ExtensionStore) GetRegistryURL() string {
+func (s *extensionStore) getRegistryURL() string {
 	s.cacheMu.RLock()
 	defer s.cacheMu.RUnlock()
 	return s.registryURL
 }

-func GetExtensionStore() *ExtensionStore {
+func getExtensionStore() *extensionStore {
 	extensionStoreMu.Lock()
 	defer extensionStoreMu.Unlock()
-	return extensionStore
+	return globalExtensionStore
 }

-func (s *ExtensionStore) loadDiskCache() {
+func (s *extensionStore) loadDiskCache() {
 	if s.cacheDir == "" {
 		return
 	}
@@ -197,7 +195,7 @@ func (s *ExtensionStore) loadDiskCache() {
 	}

 	var cacheData struct {
-		Registry  StoreRegistry `json:"registry"`
+		Registry  storeRegistry `json:"registry"`
 		CacheTime int64         `json:"cache_time"`
 	}

@@ -210,13 +208,13 @@ func (s *ExtensionStore) loadDiskCache() {
 	LogDebug("ExtensionStore", "Loaded %d extensions from disk cache", len(s.cache.Extensions))
 }

-func (s *ExtensionStore) saveDiskCache() {
+func (s *extensionStore) saveDiskCache() {
 	if s.cacheDir == "" || s.cache == nil {
 		return
 	}

 	cacheData := struct {
-		Registry  StoreRegistry `json:"registry"`
+		Registry  storeRegistry `json:"registry"`
 		CacheTime int64         `json:"cache_time"`
 	}{
 		Registry:  *s.cache,
@@ -232,11 +230,10 @@ func (s *ExtensionStore) saveDiskCache() {
 	os.WriteFile(cachePath, data, 0644)
 }

-func (s *ExtensionStore) FetchRegistry(forceRefresh bool) (*StoreRegistry, error) {
+func (s *extensionStore) fetchRegistry(forceRefresh bool) (*storeRegistry, error) {
 	s.cacheMu.Lock()
 	defer s.cacheMu.Unlock()

-	// Check if a registry URL has been configured
 	if s.registryURL == "" {
 		return nil, fmt.Errorf("no registry URL configured. Please add a repository URL first")
 	}
@@ -253,7 +250,17 @@ func (s *ExtensionStore) FetchRegistry(forceRefresh bool) (*StoreRegistry, error
 	LogInfo("ExtensionStore", "Fetching registry from %s", s.registryURL)

 	client := NewHTTPClientWithTimeout(30 * time.Second)
-	resp, err := client.Get(s.registryURL)
+	req, err := http.NewRequest(http.MethodGet, s.registryURL, nil)
+	if err != nil {
+		if s.cache != nil {
+			LogWarn("ExtensionStore", "Failed to build registry request, using cached registry: %v", err)
+			return s.cache, nil
+		}
+		return nil, fmt.Errorf("failed to build registry request: %w", err)
+	}
+	req.Header.Set("Cache-Control", "no-cache")
+	req.Header.Set("Pragma", "no-cache")
+	resp, err := client.Do(req)
 	if err != nil {
 		if s.cache != nil {
 			LogWarn("ExtensionStore", "Network error, using cached registry: %v", err)
@@ -276,7 +283,7 @@ func (s *ExtensionStore) FetchRegistry(forceRefresh bool) (*StoreRegistry, error
 		return nil, fmt.Errorf("failed to read registry: %w", err)
 	}

-	var registry StoreRegistry
+	var registry storeRegistry
 	if err := json.Unmarshal(body, &registry); err != nil {
 		return nil, fmt.Errorf("failed to parse registry: %w", err)
 	}
@@ -289,13 +296,13 @@ func (s *ExtensionStore) FetchRegistry(forceRefresh bool) (*StoreRegistry, error
 	return &registry, nil
 }

-func (s *ExtensionStore) GetExtensionsWithStatus() ([]StoreExtensionResponse, error) {
-	registry, err := s.FetchRegistry(false)
+func (s *extensionStore) getExtensionsWithStatus(forceRefresh bool) ([]storeExtensionResponse, error) {
+	registry, err := s.fetchRegistry(forceRefresh)
 	if err != nil {
 		return nil, err
 	}

-	manager := GetExtensionManager()
+	manager := getExtensionManager()
 	installed := make(map[string]string) // id -> version

 	if manager != nil {
@@ -304,29 +311,32 @@ func (s *ExtensionStore) GetExtensionsWithStatus() ([]StoreExtensionResponse, er
 		}
 	}

-	result := make([]StoreExtensionResponse, len(registry.Extensions))
-	for i, ext := range registry.Extensions {
-		resp := ext.ToResponse()
+	LogDebug("ExtensionStore", "Building store response for %d registry extensions (%d installed)", len(registry.Extensions), len(installed))

+	result := make([]storeExtensionResponse, 0, len(registry.Extensions))
+	for i := range registry.Extensions {
+		ext := &registry.Extensions[i]
+		resp := ext.toResponse()
 		if installedVersion, ok := installed[ext.ID]; ok {
 			resp.IsInstalled = true
 			resp.InstalledVersion = installedVersion
 			resp.HasUpdate = compareVersions(ext.Version, installedVersion) > 0
 		}

-		result[i] = resp
+		result = append(result, resp)
 	}

+	LogDebug("ExtensionStore", "Built store response payload for %d extensions", len(result))
 	return result, nil
 }

-func (s *ExtensionStore) DownloadExtension(extensionID string, destPath string) error {
-	registry, err := s.FetchRegistry(false)
+func (s *extensionStore) downloadExtension(extensionID string, destPath string) error {
+	registry, err := s.fetchRegistry(false)
 	if err != nil {
 		return err
 	}

-	var ext *StoreExtension
+	var ext *storeExtension
 	for _, e := range registry.Extensions {
 		if e.ID == extensionID {
 			ext = &e
@@ -345,7 +355,13 @@ func (s *ExtensionStore) DownloadExtension(extensionID string, destPath string)
 	LogInfo("ExtensionStore", "Downloading %s from %s", ext.getDisplayName(), ext.getDownloadURL())

 	client := NewHTTPClientWithTimeout(5 * time.Minute)
-	resp, err := client.Get(ext.getDownloadURL())
+	req, err := http.NewRequest(http.MethodGet, ext.getDownloadURL(), nil)
+	if err != nil {
+		return fmt.Errorf("failed to build download request: %w", err)
+	}
+	req.Header.Set("Cache-Control", "no-cache")
+	req.Header.Set("Pragma", "no-cache")
+	resp, err := client.Do(req)
 	if err != nil {
 		return fmt.Errorf("failed to download: %w", err)
 	}
@@ -371,33 +387,22 @@ func (s *ExtensionStore) DownloadExtension(extensionID string, destPath string)
 	return nil
 }

-// ResolveRegistryURL normalises a user-supplied URL into a direct registry.json URL.
-//
-// Accepted formats:
-//   - https://raw.githubusercontent.com/owner/repo/<branch>/registry.json  → returned as-is
-//   - https://github.com/owner/repo  (with optional trailing path / .git)  → resolved via
-//     the GitHub API to discover the default branch, then converted to the raw URL
-//   - Any other HTTPS URL  → returned as-is (assumed to be a direct link)
-func ResolveRegistryURL(input string) (string, error) {
+func resolveRegistryURL(input string) (string, error) {
 	input = strings.TrimSpace(input)
 	if input == "" {
 		return "", fmt.Errorf("registry URL is empty")
 	}

-	// Already a fully-qualified raw URL – keep it.
 	if strings.Contains(input, "raw.githubusercontent.com") {
 		return input, nil
 	}

-	// Try to match https://github.com/<owner>/<repo>[/...]
 	const ghPrefix = "https://github.com/"
 	if !strings.HasPrefix(input, ghPrefix) {
-		// Also accept http:// and upgrade silently.
 		const ghPrefixHTTP = "http://github.com/"
 		if strings.HasPrefix(input, ghPrefixHTTP) {
 			input = "https://github.com/" + input[len(ghPrefixHTTP):]
 		} else {
-			// Not a GitHub URL – return as-is.
 			return input, nil
 		}
 	}
@@ -417,8 +422,6 @@ func ResolveRegistryURL(input string) (string, error) {
 	return resolved, nil
 }

-// resolveGitHubDefaultBranch calls the GitHub API to discover the repository's
-// default branch.  Falls back to "main" on any error.
 func resolveGitHubDefaultBranch(owner, repo string) string {
 	apiURL := fmt.Sprintf("https://api.github.com/repos/%s/%s", owner, repo)
 	client := NewHTTPClientWithTimeout(10 * time.Second)
@@ -460,7 +463,7 @@ func requireHTTPSURL(rawURL string, context string) error {
 	return nil
 }

-func (s *ExtensionStore) GetCategories() []string {
+func (s *extensionStore) getCategories() []string {
 	return []string{
 		CategoryMetadata,
 		CategoryDownload,
@@ -470,8 +473,8 @@ func (s *ExtensionStore) GetCategories() []string {
 	}
 }

-func (s *ExtensionStore) SearchExtensions(query string, category string) ([]StoreExtensionResponse, error) {
-	extensions, err := s.GetExtensionsWithStatus()
+func (s *extensionStore) searchExtensions(query string, category string) ([]storeExtensionResponse, error) {
+	extensions, err := s.getExtensionsWithStatus(false)
 	if err != nil {
 		return nil, err
 	}
@@ -480,7 +483,7 @@ func (s *ExtensionStore) SearchExtensions(query string, category string) ([]Stor
 		return extensions, nil
 	}

-	var result []StoreExtensionResponse
+	result := make([]storeExtensionResponse, 0, len(extensions))
 	queryLower := toLower(query)

 	for _, ext := range extensions {
@@ -491,9 +494,7 @@ func (s *ExtensionStore) SearchExtensions(query string, category string) ([]Stor
 		if query != "" {
 			if !containsIgnoreCase(ext.Name, queryLower) &&
 				!containsIgnoreCase(ext.DisplayName, queryLower) &&
-				!containsIgnoreCase(ext.Description, queryLower) &&
-				!containsIgnoreCase(ext.Author, queryLower) {
-				// Check tags
+				!containsIgnoreCase(ext.Description, queryLower) {
 				found := false
 				for _, tag := range ext.Tags {
 					if containsIgnoreCase(tag, queryLower) {
@@ -513,7 +514,7 @@ func (s *ExtensionStore) SearchExtensions(query string, category string) ([]Stor
 	return result, nil
 }

-func (s *ExtensionStore) ClearCache() {
+func (s *extensionStore) clearCache() {
 	s.cacheMu.Lock()
 	defer s.cacheMu.Unlock()

@@ -1,8 +1,12 @@
 package gobackend

 import (
+	"context"
+	"errors"
+	"net/http"
 	"path/filepath"
 	"testing"
+	"time"

 	"github.com/dop251/goja"
 )
@@ -12,7 +16,6 @@ func TestParseManifest_Valid(t *testing.T) {
 		"name": "test-provider",
 		"displayName": "Test Provider",
 		"version": "1.0.0",
-		"author": "Test Author",
 		"description": "A test extension",
 		"type": ["metadata_provider"],
 		"permissions": {
@@ -43,10 +46,26 @@ func TestParseManifest_Valid(t *testing.T) {
 	}
 }

+func TestExtensionManifestStopsProviderFallback(t *testing.T) {
+	modernManifest := &ExtensionManifest{StopProviderFallback: true}
+	if !modernManifest.StopsProviderFallback() {
+		t.Fatal("expected stopProviderFallback to stop provider fallback")
+	}
+
+	legacyManifest := &ExtensionManifest{SkipBuiltInFallback: true}
+	if !legacyManifest.StopsProviderFallback() {
+		t.Fatal("expected legacy skipBuiltInFallback to stop provider fallback")
+	}
+
+	defaultManifest := &ExtensionManifest{}
+	if defaultManifest.StopsProviderFallback() {
+		t.Fatal("expected default manifest to allow provider fallback")
+	}
+}
+
 func TestParseManifest_MissingName(t *testing.T) {
 	invalidManifest := `{
 		"version": "1.0.0",
-		"author": "Test Author",
 		"description": "A test extension",
 		"type": ["metadata_provider"]
 	}`
@@ -61,7 +80,6 @@ func TestParseManifest_MissingType(t *testing.T) {
 	invalidManifest := `{
 		"name": "test-provider",
 		"version": "1.0.0",
-		"author": "Test Author",
 		"description": "A test extension"
 	}`

@@ -98,8 +116,7 @@ func TestIsDomainAllowed(t *testing.T) {
 }

 func TestExtensionRuntime_NetworkSandbox(t *testing.T) {
-	// Create a mock extension with limited network permissions
-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID: "test-ext",
 		Manifest: &ExtensionManifest{
 			Name: "test-ext",
@@ -110,7 +127,7 @@ func TestExtensionRuntime_NetworkSandbox(t *testing.T) {
 		DataDir: t.TempDir(),
 	}

-	runtime := NewExtensionRuntime(ext)
+	runtime := newExtensionRuntime(ext)

 	if err := runtime.validateDomain("https://api.allowed.com/path"); err != nil {
 		t.Errorf("Expected api.allowed.com to be allowed, got error: %v", err)
@@ -127,12 +144,21 @@ func TestExtensionRuntime_NetworkSandbox(t *testing.T) {
 	if err := runtime.validateDomain("https://notallowed.com/path"); err == nil {
 		t.Error("Expected notallowed.com to be denied")
 	}
+
+	if err := runtime.validateDomain("http://api.allowed.com/path"); err == nil {
+		t.Error("Expected http URL to be denied without allowHttp")
+	}
+
+	ext.Manifest.Permissions.AllowHTTP = true
+	if err := runtime.validateDomain("http://api.allowed.com/path"); err != nil {
+		t.Errorf("Expected http URL to be allowed with allowHttp, got error: %v", err)
+	}
 }

 func TestExtensionRuntime_FileSandbox(t *testing.T) {
 	tempDir := t.TempDir()

-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID: "test-ext",
 		Manifest: &ExtensionManifest{
 			Name: "test-ext",
@@ -143,7 +169,7 @@ func TestExtensionRuntime_FileSandbox(t *testing.T) {
 		DataDir: tempDir,
 	}

-	runtime := NewExtensionRuntime(ext)
+	runtime := newExtensionRuntime(ext)

 	validPath, err := runtime.validatePath("test.txt")
 	if err != nil {
@@ -177,7 +203,7 @@ func TestExtensionRuntime_FileSandbox(t *testing.T) {
 		t.Error("Expected absolute path to be blocked")
 	}

-	extNoFile := &LoadedExtension{
+	extNoFile := &loadedExtension{
 		ID: "test-ext-no-file",
 		Manifest: &ExtensionManifest{
 			Name: "test-ext-no-file",
@@ -187,7 +213,7 @@ func TestExtensionRuntime_FileSandbox(t *testing.T) {
 		},
 		DataDir: tempDir,
 	}
-	runtimeNoFile := NewExtensionRuntime(extNoFile)
+	runtimeNoFile := newExtensionRuntime(extNoFile)
 	_, err = runtimeNoFile.validatePath("test.txt")
 	if err == nil {
 		t.Error("Expected file access to be denied without file permission")
@@ -195,7 +221,7 @@ func TestExtensionRuntime_FileSandbox(t *testing.T) {
 }

 func TestExtensionRuntime_UtilityFunctions(t *testing.T) {
-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID: "test-ext",
 		Manifest: &ExtensionManifest{
 			Name: "test-ext",
@@ -203,7 +229,7 @@ func TestExtensionRuntime_UtilityFunctions(t *testing.T) {
 		DataDir: t.TempDir(),
 	}

-	runtime := NewExtensionRuntime(ext)
+	runtime := newExtensionRuntime(ext)
 	vm := goja.New()
 	runtime.RegisterAPIs(vm)

@@ -235,15 +261,177 @@ func TestExtensionRuntime_UtilityFunctions(t *testing.T) {
 	if err != nil {
 		t.Fatalf("stringifyJSON failed: %v", err)
 	}
-	// JSON output may vary in order, just check it's valid
 	if result.String() == "" {
 		t.Error("Expected non-empty JSON string")
 	}
+
+	result, err = vm.RunString(`utils.sleep(1)`)
+	if err != nil {
+		t.Fatalf("sleep failed: %v", err)
+	}
+	if !result.ToBoolean() {
+		t.Error("Expected sleep to complete successfully")
+	}
+
+	runtime.setActiveDownloadItemID("test-item")
+	cancelDownload("test-item")
+	t.Cleanup(func() {
+		clearDownloadCancel("test-item")
+		runtime.clearActiveDownloadItemID()
+	})
+
+	result, err = vm.RunString(`utils.isDownloadCancelled()`)
+	if err != nil {
+		t.Fatalf("isDownloadCancelled failed: %v", err)
+	}
+	if !result.ToBoolean() {
+		t.Error("Expected active download cancellation to be visible to JS")
+	}
+
+	SetAppVersion("4.2.2")
+	t.Cleanup(func() {
+		SetAppVersion("")
+	})
+
+	result, err = vm.RunString(`utils.appVersion()`)
+	if err != nil {
+		t.Fatalf("appVersion failed: %v", err)
+	}
+	if got := result.String(); got != "4.2.2" {
+		t.Fatalf("Expected appVersion 4.2.2, got %q", got)
+	}
+
+	result, err = vm.RunString(`utils.appUserAgent()`)
+	if err != nil {
+		t.Fatalf("appUserAgent failed: %v", err)
+	}
+	if got := result.String(); got != "SpotiFLAC-Mobile/4.2.2" {
+		t.Fatalf("Expected appUserAgent SpotiFLAC-Mobile/4.2.2, got %q", got)
+	}
+
+	result, err = vm.RunString(`utils.sleep(50)`)
+	if err != nil {
+		t.Fatalf("cancel-aware sleep failed: %v", err)
+	}
+	if result.ToBoolean() {
+		t.Error("Expected sleep to abort when download is cancelled")
+	}
+}
+
+func TestExtensionRuntime_BindDownloadCancelContext(t *testing.T) {
+	ext := &loadedExtension{
+		ID: "test-ext",
+		Manifest: &ExtensionManifest{
+			Name: "test-ext",
+		},
+		DataDir: t.TempDir(),
+	}
+
+	runtime := newExtensionRuntime(ext)
+	runtime.setActiveDownloadItemID("test-item")
+	t.Cleanup(func() {
+		clearDownloadCancel("test-item")
+		runtime.clearActiveDownloadItemID()
+	})
+
+	req, err := http.NewRequest("GET", "https://api.example.com/test", nil)
+	if err != nil {
+		t.Fatalf("NewRequest failed: %v", err)
+	}
+
+	req = runtime.bindDownloadCancelContext(req)
+	cancelDownload("test-item")
+
+	select {
+	case <-req.Context().Done():
+	case <-time.After(500 * time.Millisecond):
+		t.Fatal("Expected bound request context to be cancelled")
+	}
+
+	if req.Context().Err() == nil {
+		t.Fatal("Expected request context error after cancellation")
+	}
+}
+
+func TestExtensionRuntime_BindDownloadCancelContextPreservesPreCancelledState(t *testing.T) {
+	ext := &loadedExtension{
+		ID: "test-ext",
+		Manifest: &ExtensionManifest{
+			Name: "test-ext",
+		},
+		DataDir: t.TempDir(),
+	}
+
+	runtime := newExtensionRuntime(ext)
+	runtime.setActiveDownloadItemID("test-item")
+	cancelDownload("test-item")
+	t.Cleanup(func() {
+		clearDownloadCancel("test-item")
+		runtime.clearActiveDownloadItemID()
+	})
+
+	req, err := http.NewRequest("GET", "https://api.example.com/test", nil)
+	if err != nil {
+		t.Fatalf("NewRequest failed: %v", err)
+	}
+
+	req = runtime.bindDownloadCancelContext(req)
+
+	select {
+	case <-req.Context().Done():
+	case <-time.After(500 * time.Millisecond):
+		t.Fatal("Expected pre-cancelled request context to stay cancelled")
+	}
+
+	if req.Context().Err() == nil {
+		t.Fatal("Expected request context error for pre-cancelled item")
+	}
+}
+
+func TestRunWithTimeoutContextCancelsExecution(t *testing.T) {
+	vm := goja.New()
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	_, err := RunWithTimeoutContextAndRecover(ctx, vm, `while (true) {}`, 5*time.Second)
+	if !errors.Is(err, ErrExtensionRequestCancelled) {
+		t.Fatalf("expected extension request cancellation, got %v", err)
+	}
+}
+
+func TestExtensionRuntime_BindExtensionRequestCancelContext(t *testing.T) {
+	ext := &loadedExtension{
+		ID: "test-ext",
+		Manifest: &ExtensionManifest{
+			Name: "test-ext",
+		},
+		DataDir: t.TempDir(),
+	}
+	runtime := newExtensionRuntime(ext)
+
+	const requestID = "test-extension-request"
+	clearExtensionRequestCancel(requestID)
+	defer clearExtensionRequestCancel(requestID)
+
+	runtime.setActiveRequestID(requestID)
+	defer runtime.clearActiveRequestID()
+
+	req, err := http.NewRequest(http.MethodGet, "https://example.com", nil)
+	if err != nil {
+		t.Fatalf("new request: %v", err)
+	}
+	req = runtime.bindDownloadCancelContext(req)
+
+	cancelExtensionRequest(requestID)
+	select {
+	case <-req.Context().Done():
+	case <-time.After(time.Second):
+		t.Fatal("expected request context to be cancelled")
+	}
 }

 func TestExtensionRuntime_SSRFProtection(t *testing.T) {
-	// Create extension with limited network permissions
-	ext := &LoadedExtension{
+	ext := &loadedExtension{
 		ID: "test-ext",
 		Manifest: &ExtensionManifest{
 			Name: "test-ext",
@@ -254,7 +442,7 @@ func TestExtensionRuntime_SSRFProtection(t *testing.T) {
 		DataDir: t.TempDir(),
 	}

-	runtime := NewExtensionRuntime(ext)
+	runtime := newExtensionRuntime(ext)

 	privateIPs := []string{
 		"http://localhost/admin",
@@ -20,11 +20,22 @@ func (e *JSExecutionError) Error() string {
 }

 func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goja.Value, error) {
+	return RunWithTimeoutContext(context.Background(), vm, script, timeout)
+}
+
+func RunWithTimeoutContext(ctx context.Context, vm *goja.Runtime, script string, timeout time.Duration) (goja.Value, error) {
+	if vm == nil {
+		return nil, fmt.Errorf("extension runtime unavailable")
+	}
+
 	if timeout <= 0 {
 		timeout = DefaultJSTimeout
 	}

-	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	ctx, cancel := context.WithTimeout(ctx, timeout)
 	defer cancel()

 	type result struct {
@@ -49,7 +60,7 @@ func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goj
 						IsTimeout: true,
 					}}
 				} else {
-					GoLog("[ExtensionRuntime] panic during JS execution: %v\n%s\n", r, string(debug.Stack()))
+					GoLog("[extensionRuntime] panic during JS execution: %v\n%s\n", r, string(debug.Stack()))
 					resultCh <- result{nil, fmt.Errorf("panic during execution: %v", r)}
 				}
 			}
@@ -63,14 +74,27 @@ func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goj
 	case res := <-resultCh:
 		return res.value, res.err
 	case <-ctx.Done():
+		cancelled := ctx.Err() == context.Canceled
 		interruptMu.Lock()
 		interrupted = true
 		interruptMu.Unlock()

-		vm.Interrupt("execution timeout")
+		if cancelled {
+			vm.Interrupt("extension request cancelled")
+		} else {
+			vm.Interrupt("execution timeout")
+		}

+		// MUST wait for the goroutine to finish before returning.
+		// The Goja VM is NOT thread-safe — if we return while the goroutine
+		// is still executing JS (e.g. blocked on an HTTP call), the next
+		// caller will access the VM concurrently and crash with a nil
+		// pointer dereference.
 		select {
 		case res := <-resultCh:
+			if cancelled {
+				return nil, ErrExtensionRequestCancelled
+			}
 			if res.err != nil {
 				return nil, res.err
 			}
@@ -78,7 +102,13 @@ func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goj
 				Message:   "execution timeout exceeded",
 				IsTimeout: true,
 			}
-		case <-time.After(1 * time.Second):
+		case <-time.After(60 * time.Second):
+			// Goroutine is truly stuck (e.g. HTTP read with no timeout).
+			// Log a warning — the VM should NOT be reused after this.
+			GoLog("[extensionRuntime] WARNING: JS goroutine did not exit within 60s after interrupt, VM may be unsafe\n")
+			if cancelled {
+				return nil, ErrExtensionRequestCancelled
+			}
 			return nil, &JSExecutionError{
 				Message:   "execution timeout exceeded (force)",
 				IsTimeout: true,
@@ -90,10 +120,15 @@ func RunWithTimeout(vm *goja.Runtime, script string, timeout time.Duration) (goj
 // RunWithTimeoutAndRecover runs JS with timeout and clears interrupt state after
 // This should be used when you want to continue using the VM after a timeout
 func RunWithTimeoutAndRecover(vm *goja.Runtime, script string, timeout time.Duration) (goja.Value, error) {
-	result, err := RunWithTimeout(vm, script, timeout)
+	return RunWithTimeoutContextAndRecover(context.Background(), vm, script, timeout)
+}

-	// Clear any interrupt state so VM can be reused
-	vm.ClearInterrupt()
+func RunWithTimeoutContextAndRecover(ctx context.Context, vm *goja.Runtime, script string, timeout time.Duration) (goja.Value, error) {
+	result, err := RunWithTimeoutContext(ctx, vm, script, timeout)
+
+	if vm != nil {
+		vm.ClearInterrupt()
+	}

 	return result, err
 }
@@ -6,6 +6,8 @@ import (
 	"strconv"
 	"strings"
 	"time"
+	"unicode"
+	"unicode/utf8"
 )

 var (
@@ -17,24 +19,66 @@ var (
 )

 func sanitizeFilename(filename string) string {
-	sanitized := invalidChars.ReplaceAllString(filename, "_")
+	sanitized := strings.ReplaceAll(filename, "/", " ")
+	sanitized = invalidChars.ReplaceAllString(sanitized, " ")

+	var builder strings.Builder
+	for _, r := range sanitized {
+		if r < 0x20 && r != 0x09 && r != 0x0A && r != 0x0D {
+			continue
+		}
+		if r == 0x7F {
+			continue
+		}
+		if unicode.IsControl(r) && r != 0x09 && r != 0x0A && r != 0x0D {
+			continue
+		}
+		builder.WriteRune(r)
+	}
+
+	sanitized = builder.String()
 	sanitized = strings.TrimSpace(sanitized)
-	sanitized = strings.Trim(sanitized, ".")
-
+	sanitized = strings.Trim(sanitized, ". ")
+	sanitized = strings.Join(strings.Fields(sanitized), " ")
 	sanitized = multiUnderscore.ReplaceAllString(sanitized, "_")
+	sanitized = strings.Trim(sanitized, "_ ")
+
+	if !utf8.ValidString(sanitized) {
+		sanitized = strings.ToValidUTF8(sanitized, "_")
+	}

 	if len(sanitized) > 200 {
-		sanitized = sanitized[:200]
+		sanitized = truncateUTF8Bytes(sanitized, 200)
+		sanitized = strings.TrimSpace(strings.Trim(sanitized, ". "))
+		sanitized = strings.Trim(sanitized, "_ ")
 	}

 	if sanitized == "" {
-		sanitized = "untitled"
+		return "Unknown"
 	}

 	return sanitized
 }

+func truncateUTF8Bytes(value string, maxBytes int) string {
+	if maxBytes <= 0 || len(value) <= maxBytes {
+		return value
+	}
+
+	used := 0
+	for i, r := range value {
+		runeLen := utf8.RuneLen(r)
+		if runeLen < 0 {
+			runeLen = len(string(r))
+		}
+		if used+runeLen > maxBytes {
+			return value[:i]
+		}
+		used += runeLen
+	}
+	return value
+}
+
 func buildFilenameFromTemplate(template string, metadata map[string]interface{}) string {
 	if template == "" {
 		template = "{artist} - {title}"
@@ -1,6 +1,10 @@
 package gobackend

-import "testing"
+import (
+	"strings"
+	"testing"
+	"unicode/utf8"
+)

 func TestBuildFilenameFromTemplate_WithRawTrackAndDisc(t *testing.T) {
 	metadata := map[string]interface{}{
@@ -83,3 +87,28 @@ func TestBuildFilenameFromTemplate_DateStrftimeFormattingWithYearOnly(t *testing
 		t.Fatalf("expected %q, got %q", expected, formatted)
 	}
 }
+
+func TestSanitizeFilenameMatchesDesktopSpacingBehavior(t *testing.T) {
+	got := sanitizeFilename(`  "Text In Quotes"?%* / Demo  `)
+	want := "Text In Quotes % Demo"
+	if got != want {
+		t.Fatalf("expected %q, got %q", want, got)
+	}
+}
+
+func TestSanitizeFilenameFallsBackToUnknownWhenEmpty(t *testing.T) {
+	got := sanitizeFilename(`<>:"/\|?*`)
+	if got != "Unknown" {
+		t.Fatalf("expected %q, got %q", "Unknown", got)
+	}
+}
+
+func TestSanitizeFilenameTruncatesWithoutSplittingUTF8(t *testing.T) {
+	got := sanitizeFilename(strings.Repeat("あ", 80))
+	if !utf8.ValidString(got) {
+		t.Fatalf("sanitizeFilename returned invalid UTF-8: %q", got)
+	}
+	if len(got) > 200 {
+		t.Fatalf("sanitizeFilename length = %d, want <= 200", len(got))
+	}
+}
--- a/Show More
+++ b/Show More