diff --git a/android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt b/android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt
index 327bc820..53cc7fa3 100644
--- a/android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt
+++ b/android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt
@@ -2198,14 +2198,6 @@ class MainActivity: FlutterFragmentActivity() {
                             }
                             result.success(null)
                         }
-                        "checkAvailability" -> {
-                            val spotifyId = call.argument<String>("spotify_id") ?: ""
-                            val isrc = call.argument<String>("isrc") ?: ""
-                            val response = withContext(Dispatchers.IO) {
-                                Gobackend.checkAvailability(spotifyId, isrc)
-                            }
-                            result.success(response)
-                        }
                         "downloadByStrategy" -> {
                             val requestJson = call.arguments as String
                             val response = withContext(Dispatchers.IO) {
@@ -3038,13 +3030,6 @@ class MainActivity: FlutterFragmentActivity() {
                             }
                             result.success(payload)
                         }
-                        "preWarmTrackCache" -> {
-                            val tracksJson = call.argument<String>("tracks") ?: "[]"
-                            withContext(Dispatchers.IO) {
-                                Gobackend.preWarmTrackCacheJSON(tracksJson)
-                            }
-                            result.success(null)
-                        }
                         "getTrackCacheSize" -> {
                             val size = withContext(Dispatchers.IO) {
                                 Gobackend.getTrackCacheSize()
@@ -3097,22 +3082,6 @@ class MainActivity: FlutterFragmentActivity() {
                             }
                             result.success(response)
                         }
-                        "checkAvailabilityFromDeezerID" -> {
-                            val deezerTrackId = call.argument<String>("deezer_track_id") ?: ""
-                            val response = withContext(Dispatchers.IO) {
-                                Gobackend.checkAvailabilityFromDeezerID(deezerTrackId)
-                            }
-                            result.success(response)
-                        }
-                        "checkAvailabilityByPlatformID" -> {
-                            val platform = call.argument<String>("platform") ?: ""
-                            val entityType = call.argument<String>("entity_type") ?: ""
-                            val entityId = call.argument<String>("entity_id") ?: ""
-                            val response = withContext(Dispatchers.IO) {
-                                Gobackend.checkAvailabilityByPlatformID(platform, entityType, entityId)
-                            }
-                            result.success(response)
-                        }
                         "getSpotifyIDFromDeezerTrack" -> {
                             val deezerTrackId = call.argument<String>("deezer_track_id") ?: ""
                             val response = withContext(Dispatchers.IO) {
diff --git a/go_backend/audio_metadata.go b/go_backend/audio_metadata.go
index 9cb0c1c9..0c8aba26 100644
--- a/go_backend/audio_metadata.go
+++ b/go_backend/audio_metadata.go
@@ -186,7 +186,7 @@ func parseID3v22Frames(data []byte, metadata *AudioMetadata, tagUnsync bool) {
 		case "TCR":
 			metadata.Copyright = value
 		case "ULT":
-			if v := extractLyricsFrame(frameData); v != "" && metadata.Lyrics == "" {
+			if v := extractLangTextFrame(frameData); v != "" && metadata.Lyrics == "" {
 				metadata.Lyrics = v
 			}
 		case "TXX":
@@ -307,11 +307,11 @@ func parseID3v23Frames(data []byte, metadata *AudioMetadata, version byte, tagUn
 		case "TCOP":
 			metadata.Copyright = value
 		case "COMM":
-			if v := extractCommentFrame(frameData); v != "" {
+			if v := extractLangTextFrame(frameData); v != "" {
 				metadata.Comment = v
 			}
 		case "USLT":
-			if v := extractLyricsFrame(frameData); v != "" && metadata.Lyrics == "" {
+			if v := extractLangTextFrame(frameData); v != "" && metadata.Lyrics == "" {
 				metadata.Lyrics = v
 			}
 		case "TXXX":
@@ -391,7 +391,9 @@ func extractTextFrame(data []byte) string {
 	}
 }
 
-func extractCommentFrame(data []byte) string {
+// extractLangTextFrame decodes ID3 frames with an encoding byte, 3-byte
+// language code, and null-terminated descriptor before the text (COMM, USLT).
+func extractLangTextFrame(data []byte) string {
 	if len(data) < 5 {
 		return ""
 	}
@@ -426,42 +428,6 @@ func extractCommentFrame(data []byte) string {
 	return extractTextFrame(framed)
 }
 
-func extractLyricsFrame(data []byte) string {
-	if len(data) < 5 {
-		return ""
-	}
-
-	encoding := data[0]
-	rest := data[4:]
-
-	var text []byte
-	switch encoding {
-	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:
-		idx := bytes.IndexByte(rest, 0)
-		if idx >= 0 && idx+1 < len(rest) {
-			text = rest[idx+1:]
-		} else {
-			text = rest
-		}
-	}
-
-	if len(text) == 0 {
-		return ""
-	}
-
-	framed := make([]byte, 1+len(text))
-	framed[0] = encoding
-	copy(framed[1:], text)
-	return extractTextFrame(framed)
-}
-
 func extractUserTextFrame(data []byte) (string, string) {
 	if len(data) < 2 {
 		return "", ""
@@ -582,11 +548,6 @@ func cleanGenre(genre string) string {
 	return genre
 }
 
-func parseTrackNumber(s string) int {
-	num, _ := parseIndexPair(s)
-	return num
-}
-
 func parseIndexPair(s string) (int, int) {
 	s = strings.TrimSpace(s)
 	if s == "" {
@@ -1554,10 +1515,6 @@ func parseFLACPictureBlock(data []byte) ([]byte, string) {
 	return imageData, mimeType
 }
 
-func extractAnyCoverArt(filePath string) ([]byte, string, error) {
-	return extractAnyCoverArtWithHint(filePath, "")
-}
-
 func extractAnyCoverArtWithHint(filePath, displayNameHint string) ([]byte, string, error) {
 	ext := strings.ToLower(filepath.Ext(filePath))
 	if ext == "" {
@@ -1605,14 +1562,6 @@ func extractAnyCoverArtWithHint(filePath, displayNameHint string) ([]byte, strin
 	}
 }
 
-func SaveCoverToCache(filePath, cacheDir string) (string, error) {
-	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 != "" {
diff --git a/go_backend/audio_metadata_supplement_test.go b/go_backend/audio_metadata_supplement_test.go
index eb83b07d..c752f01f 100644
--- a/go_backend/audio_metadata_supplement_test.go
+++ b/go_backend/audio_metadata_supplement_test.go
@@ -85,9 +85,6 @@ func TestAudioMetadataID3ParsingBranches(t *testing.T) {
 	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)
 	}
@@ -424,9 +421,6 @@ func TestOggMetadataQualityAndCoverHelpers(t *testing.T) {
 	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)
@@ -438,17 +432,6 @@ func TestOggMetadataQualityAndCoverHelpers(t *testing.T) {
 	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")
 	}
diff --git a/go_backend/cover.go b/go_backend/cover.go
index c274bedc..0c8c3830 100644
--- a/go_backend/cover.go
+++ b/go_backend/cover.go
@@ -247,17 +247,3 @@ func upgradeQobuzCover(coverURL string) string {
 	}
 	return upgraded
 }
-
-func GetCoverFromSpotify(imageURL string, maxQuality bool) string {
-	if imageURL == "" {
-		return ""
-	}
-
-	result := convertSmallToMedium(imageURL)
-
-	if maxQuality {
-		result = upgradeToMaxQuality(result)
-	}
-
-	return result
-}
diff --git a/go_backend/exports.go b/go_backend/exports.go
index 1a519c18..eee7b700 100644
--- a/go_backend/exports.go
+++ b/go_backend/exports.go
@@ -40,16 +40,6 @@ func ReleaseMemory() {
 	debug.FreeOSMemory()
 }
 
-func CheckAvailability(spotifyID, isrc string) (string, error) {
-	client := NewSongLinkClient()
-	availability, err := client.CheckTrackAvailability(spotifyID, isrc)
-	if err != nil {
-		return "", err
-	}
-
-	return marshalJSONString(availability)
-}
-
 // SetSongLinkNetworkOptions is kept for backward compatibility.
 func SetSongLinkNetworkOptions(allowHTTP, insecureTLS bool) {
 	SetNetworkCompatibilityOptions(allowHTTP, insecureTLS)
diff --git a/go_backend/exports_deezer.go b/go_backend/exports_deezer.go
index fbbc60b1..2b4443c4 100644
--- a/go_backend/exports_deezer.go
+++ b/go_backend/exports_deezer.go
@@ -2,53 +2,19 @@ package gobackend
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"strings"
 	"time"
 )
 
-func PreWarmTrackCacheJSON(tracksJSON string) (string, error) {
-	var tracks []struct {
-		ISRC       string `json:"isrc"`
-		TrackName  string `json:"track_name"`
-		ArtistName string `json:"artist_name"`
-		SpotifyID  string `json:"spotify_id"`
-		Service    string `json:"service"`
-	}
-
-	if err := json.Unmarshal([]byte(tracksJSON), &tracks); err != nil {
-		return errorResponse("Invalid JSON: " + err.Error())
-	}
-
-	requests := make([]PreWarmCacheRequest, len(tracks))
-	for i, t := range tracks {
-		requests[i] = PreWarmCacheRequest{
-			ISRC:       t.ISRC,
-			TrackName:  t.TrackName,
-			ArtistName: t.ArtistName,
-			SpotifyID:  t.SpotifyID,
-			Service:    t.Service,
-		}
-	}
-
-	go PreWarmTrackCache(requests)
-
-	resp := map[string]any{
-		"success": true,
-		"message": fmt.Sprintf("Pre-warming cache for %d tracks in background", len(tracks)),
-	}
-
-	s, _ := marshalJSONString(resp)
-	return s, nil
-}
-
+// GetTrackCacheSize and ClearTrackIDCache back the Settings cache screen. The
+// track-ID cache is currently a no-op, so these report an empty cache and clear
+// nothing, but the gomobile export contract is kept for the Dart/Kotlin callers.
 func GetTrackCacheSize() int {
-	return GetCacheSize()
+	return 0
 }
 
 func ClearTrackIDCache() {
-	ClearTrackCache()
 }
 
 func GetDeezerRelatedArtists(artistID string, limit int) (string, error) {
@@ -237,26 +203,6 @@ func ConvertSpotifyToDeezer(resourceType, spotifyID string) (string, error) {
 	return "", fmt.Errorf("spotify to Deezer conversion only supported for tracks and albums: please search by name for %s", resourceType)
 }
 
-func CheckAvailabilityFromDeezerID(deezerTrackID string) (string, error) {
-	client := NewSongLinkClient()
-	availability, err := client.CheckAvailabilityFromDeezer(deezerTrackID)
-	if err != nil {
-		return "", err
-	}
-
-	return marshalJSONString(availability)
-}
-
-func CheckAvailabilityByPlatformID(platform, entityType, entityID string) (string, error) {
-	client := NewSongLinkClient()
-	availability, err := client.CheckAvailabilityByPlatform(platform, entityType, entityID)
-	if err != nil {
-		return "", err
-	}
-
-	return marshalJSONString(availability)
-}
-
 func GetSpotifyIDFromDeezerTrack(deezerTrackID string) (string, error) {
 	client := NewSongLinkClient()
 	return client.GetSpotifyIDFromDeezer(deezerTrackID)
diff --git a/go_backend/exports_download.go b/go_backend/exports_download.go
index 5acf503f..c176d87d 100644
--- a/go_backend/exports_download.go
+++ b/go_backend/exports_download.go
@@ -358,10 +358,6 @@ func applySongLinkRegionFromRequest(req *DownloadRequest) {
 	SetSongLinkRegion(req.SongLinkRegion)
 }
 
-func DownloadTrack(requestJSON string) (string, error) {
-	return errorResponse("Built-in download providers have been retired. Use downloadByStrategy with extension providers.")
-}
-
 // DownloadByStrategy routes all download requests through extension providers.
 func DownloadByStrategy(requestJSON string) (string, error) {
 	var req DownloadRequest
@@ -385,10 +381,6 @@ func DownloadByStrategy(requestJSON string) (string, error) {
 	return errorResponse("Extension providers are disabled; built-in download providers have been retired")
 }
 
-func DownloadWithFallback(requestJSON string) (string, error) {
-	return errorResponse("Built-in fallback has been retired. Use extension fallback through downloadByStrategy.")
-}
-
 func GetDownloadProgress() string {
 	progress := getProgress()
 	jsonBytes, _ := json.Marshal(progress)
diff --git a/go_backend/exports_extensions.go b/go_backend/exports_extensions.go
index 420e7855..328876ef 100644
--- a/go_backend/exports_extensions.go
+++ b/go_backend/exports_extensions.go
@@ -394,11 +394,6 @@ func SetExtensionFallbackProviderIDsJSON(providerIDsJSON string) error {
 	return nil
 }
 
-func GetExtensionFallbackProviderIDsJSON() (string, error) {
-	providerIDs := GetExtensionFallbackProviderIDs()
-	return marshalJSONString(providerIDs)
-}
-
 func SetMetadataProviderPriorityJSON(priorityJSON string) error {
 	var priority []string
 	if err := json.Unmarshal([]byte(priorityJSON), &priority); err != nil {
diff --git a/go_backend/exports_library.go b/go_backend/exports_library.go
index f14bee9f..b342989e 100644
--- a/go_backend/exports_library.go
+++ b/go_backend/exports_library.go
@@ -28,10 +28,6 @@ func ReadAudioMetadataJSON(filePath string) (string, error) {
 	return ReadAudioMetadata(filePath)
 }
 
-func ReadAudioMetadataWithHintJSON(filePath, displayName string) (string, error) {
-	return ReadAudioMetadataWithDisplayName(filePath, displayName)
-}
-
 func ReadAudioMetadataWithHintAndCoverCacheKeyJSON(filePath, displayName, coverCacheKey string) (string, error) {
 	return ReadAudioMetadataWithDisplayNameAndCoverCacheKey(filePath, displayName, coverCacheKey)
 }
diff --git a/go_backend/exports_songlink_lyrics_supplement_test.go b/go_backend/exports_songlink_lyrics_supplement_test.go
index 5d2c635f..be0abe81 100644
--- a/go_backend/exports_songlink_lyrics_supplement_test.go
+++ b/go_backend/exports_songlink_lyrics_supplement_test.go
@@ -1,7 +1,6 @@
 package gobackend
 
 import (
-	"context"
 	"io"
 	"net/http"
 	"os"
@@ -55,13 +54,9 @@ func TestLyricsExportWrappersWithoutNetwork(t *testing.T) {
 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 {
@@ -82,15 +77,6 @@ func TestSongLinkExportWrappersWithFakeClient(t *testing.T) {
 	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)
 	}
@@ -122,15 +108,6 @@ func TestSongLinkExportWrappersWithFakeClient(t *testing.T) {
 		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")
 	}
diff --git a/go_backend/exports_supplement_test.go b/go_backend/exports_supplement_test.go
index 99fbfa28..e82b96dc 100644
--- a/go_backend/exports_supplement_test.go
+++ b/go_backend/exports_supplement_test.go
@@ -91,18 +91,12 @@ func TestExportsJSONWrappersAndExtensionManagerSurface(t *testing.T) {
 		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")
@@ -183,12 +177,6 @@ func TestExportsJSONWrappersAndExtensionManagerSurface(t *testing.T) {
 		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")
 	}
@@ -219,9 +207,6 @@ func TestExportsJSONWrappersAndExtensionManagerSurface(t *testing.T) {
 	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)
 	}
@@ -484,9 +469,6 @@ func TestExportsJSONWrappersAndExtensionManagerSurface(t *testing.T) {
 	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)
 	}
diff --git a/go_backend/extension_health_misc_supplement_test.go b/go_backend/extension_health_misc_supplement_test.go
index 776a5b0b..94bcf6d8 100644
--- a/go_backend/extension_health_misc_supplement_test.go
+++ b/go_backend/extension_health_misc_supplement_test.go
@@ -71,11 +71,7 @@ func TestExtensionHealthClassificationAndValidation(t *testing.T) {
 	}
 }
 
-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)
-	}
+func TestCoverAndIDHSHelpers(t *testing.T) {
 	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)
 	}
@@ -89,32 +85,6 @@ func TestCoverRomajiParallelAndIDHSHelpers(t *testing.T) {
 		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)
diff --git a/go_backend/extension_runtime_file.go b/go_backend/extension_runtime_file.go
index 40b798e3..c2143129 100644
--- a/go_backend/extension_runtime_file.go
+++ b/go_backend/extension_runtime_file.go
@@ -18,13 +18,6 @@ var (
 	allowedDownloadDirsMu sync.RWMutex
 )
 
-func SetAllowedDownloadDirs(dirs []string) {
-	allowedDownloadDirsMu.Lock()
-	defer allowedDownloadDirsMu.Unlock()
-	allowedDownloadDirs = dirs
-	GoLog("[Extension] Allowed download directories set: %v\n", dirs)
-}
-
 func AddAllowedDownloadDir(dir string) {
 	allowedDownloadDirsMu.Lock()
 	defer allowedDownloadDirsMu.Unlock()
@@ -34,6 +27,15 @@ func AddAllowedDownloadDir(dir string) {
 	}
 }
 
+// SetAllowedDownloadDirs replaces the whole allow-list in one call (passing nil
+// clears it). Used by tests to reset the sandbox between cases; production code
+// appends via AddAllowedDownloadDir.
+func SetAllowedDownloadDirs(dirs []string) {
+	allowedDownloadDirsMu.Lock()
+	defer allowedDownloadDirsMu.Unlock()
+	allowedDownloadDirs = dirs
+}
+
 func isPathInAllowedDirs(absPath string) bool {
 	allowedDownloadDirsMu.RLock()
 	defer allowedDownloadDirsMu.RUnlock()
diff --git a/go_backend/extension_runtime_storage.go b/go_backend/extension_runtime_storage.go
index acdc52c4..70d00b00 100644
--- a/go_backend/extension_runtime_storage.go
+++ b/go_backend/extension_runtime_storage.go
@@ -98,16 +98,6 @@ func (r *extensionRuntime) ensureStorageLoaded() error {
 	return nil
 }
 
-func (r *extensionRuntime) loadStorage() (map[string]any, error) {
-	if err := r.ensureStorageLoaded(); err != nil {
-		return nil, err
-	}
-
-	r.storageMu.RLock()
-	defer r.storageMu.RUnlock()
-	return cloneInterfaceMap(r.storageCache), nil
-}
-
 func (r *extensionRuntime) queueStorageFlushLocked(delay time.Duration) {
 	if r.storageClosed {
 		return
diff --git a/go_backend/extension_runtime_supplement_test.go b/go_backend/extension_runtime_supplement_test.go
index 39ac5498..d35192d2 100644
--- a/go_backend/extension_runtime_supplement_test.go
+++ b/go_backend/extension_runtime_supplement_test.go
@@ -635,10 +635,6 @@ func TestExtensionStoreSettingsAndRuntimeStorage(t *testing.T) {
 	if ok := runtime.storageSet(goja.FunctionCall{Arguments: []goja.Value{vm.ToValue("key"), vm.ToValue(map[string]any{"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)
 	}
diff --git a/go_backend/extension_timeout.go b/go_backend/extension_timeout.go
index c5163320..a1b6fbe9 100644
--- a/go_backend/extension_timeout.go
+++ b/go_backend/extension_timeout.go
@@ -19,10 +19,6 @@ func (e *JSExecutionError) Error() string {
 	return e.Message
 }
 
-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")
diff --git a/go_backend/httputil_supplement_test.go b/go_backend/httputil_supplement_test.go
index d600764a..d5222f8d 100644
--- a/go_backend/httputil_supplement_test.go
+++ b/go_backend/httputil_supplement_test.go
@@ -158,9 +158,6 @@ func TestRateLimiterHelpers(t *testing.T) {
 	if limiter.Available() != 0 {
 		t.Fatalf("available after acquire = %d", limiter.Available())
 	}
-	if GetSongLinkRateLimiter() == nil {
-		t.Fatal("expected global limiter")
-	}
 }
 
 func mustNewRequest(t *testing.T, rawURL string) *http.Request {
diff --git a/go_backend/log_progress_timeout_supplement_test.go b/go_backend/log_progress_timeout_supplement_test.go
index 7b0ac755..ebb2246e 100644
--- a/go_backend/log_progress_timeout_supplement_test.go
+++ b/go_backend/log_progress_timeout_supplement_test.go
@@ -96,18 +96,8 @@ func TestProgressItemHelpersAndWriter(t *testing.T) {
 }
 
 func TestRunWithTimeoutBranches(t *testing.T) {
-	if _, err := RunWithTimeout(nil, "1 + 1", time.Millisecond); err == nil {
-		t.Fatal("expected nil VM error")
-	}
-
-	vm := goja.New()
-	value, err := RunWithTimeout(vm, "1 + 2", time.Second)
-	if err != nil || value.ToInteger() != 3 {
-		t.Fatalf("RunWithTimeout success = %v/%v", value, err)
-	}
-
 	timeoutVM := goja.New()
-	_, err = RunWithTimeoutAndRecover(timeoutVM, "for (;;) {}", 10*time.Millisecond)
+	_, err := RunWithTimeoutAndRecover(timeoutVM, "for (;;) {}", 10*time.Millisecond)
 	if err == nil {
 		t.Fatal("expected timeout error")
 	}
diff --git a/go_backend/metadata.go b/go_backend/metadata.go
index 0d463c19..69a4355f 100644
--- a/go_backend/metadata.go
+++ b/go_backend/metadata.go
@@ -218,19 +218,19 @@ func parseFlacFile(filePath string) (*flac.File, error) {
 	return f, nil
 }
 
-func EmbedMetadata(filePath string, metadata Metadata, coverPath string) error {
+// updateFlacVorbis parses a FLAC file, hands the parsed file and its Vorbis
+// comment block (created if absent) to mutate, then marshals the block back
+// into the file and saves it. Shared scaffold for all FLAC tag writers.
+func updateFlacVorbis(filePath string, mutate func(f *flac.File, cmt *flacvorbis.MetaDataBlockVorbisComment) error) error {
 	f, err := parseFlacFile(filePath)
 	if err != nil {
 		return fmt.Errorf("failed to parse FLAC file: %w", err)
 	}
 	defer f.Close()
 
-	var cmtIdx int = -1
 	var cmt *flacvorbis.MetaDataBlockVorbisComment
-
-	for idx, meta := range f.Meta {
+	for _, meta := range f.Meta {
 		if meta.Type == flac.VorbisComment {
-			cmtIdx = idx
 			cmt, err = flacvorbis.ParseFromMetaDataBlock(*meta)
 			if err != nil {
 				return fmt.Errorf("failed to parse vorbis comment: %w", err)
@@ -238,99 +238,83 @@ func EmbedMetadata(filePath string, metadata Metadata, coverPath string) error {
 			break
 		}
 	}
-
 	if cmt == nil {
 		cmt = flacvorbis.New()
 	}
 
-	writeVorbisMetadata(cmt, metadata)
-
-	cmtBlock := cmt.Marshal()
-	if cmtIdx >= 0 {
-		f.Meta[cmtIdx] = &cmtBlock
-	} else {
-		f.Meta = append(f.Meta, &cmtBlock)
+	if err := mutate(f, cmt); err != nil {
+		return err
 	}
 
-	if coverPath != "" {
-		if fileExists(coverPath) {
-			coverData, err := os.ReadFile(coverPath)
-			if err != nil {
-				fmt.Printf("[Metadata] Warning: Failed to read cover file %s: %v\n", coverPath, err)
-			} else {
-				for i := len(f.Meta) - 1; i >= 0; i-- {
-					if f.Meta[i].Type == flac.Picture {
-						f.Meta = append(f.Meta[:i], f.Meta[i+1:]...)
-					}
-				}
-
-				picBlock, err := buildPictureBlock(coverPath, coverData)
-				if err != nil {
-					fmt.Printf("[Metadata] Warning: skipping cover art: %v\n", err)
-				} else {
-					f.Meta = append(f.Meta, &picBlock)
-					fmt.Printf("[Metadata] Cover art embedded successfully (%d bytes)\n", len(coverData))
-				}
-			}
-		} else {
-			fmt.Printf("[Metadata] Warning: Cover file does not exist: %s\n", coverPath)
+	// Re-scan for the block index: mutate may have removed blocks.
+	cmtBlock := cmt.Marshal()
+	replaced := false
+	for idx, meta := range f.Meta {
+		if meta.Type == flac.VorbisComment {
+			f.Meta[idx] = &cmtBlock
+			replaced = true
+			break
 		}
 	}
+	if !replaced {
+		f.Meta = append(f.Meta, &cmtBlock)
+	}
 
 	return saveFlacFile(f, filePath)
 }
 
-func EmbedMetadataWithCoverData(filePath string, metadata Metadata, coverData []byte) error {
-	f, err := parseFlacFile(filePath)
+// replaceFlacPictures strips all Picture blocks and appends a new front cover
+// built from coverData. On error the pictures stay removed and no cover is added.
+func replaceFlacPictures(f *flac.File, coverPath string, coverData []byte) error {
+	for i := len(f.Meta) - 1; i >= 0; i-- {
+		if f.Meta[i].Type == flac.Picture {
+			f.Meta = append(f.Meta[:i], f.Meta[i+1:]...)
+		}
+	}
+
+	picBlock, err := buildPictureBlock(coverPath, coverData)
 	if err != nil {
-		return fmt.Errorf("failed to parse FLAC file: %w", err)
+		return err
 	}
-	defer f.Close()
+	f.Meta = append(f.Meta, &picBlock)
+	return nil
+}
 
-	var cmtIdx int = -1
-	var cmt *flacvorbis.MetaDataBlockVorbisComment
+func EmbedMetadata(filePath string, metadata Metadata, coverPath string) error {
+	return updateFlacVorbis(filePath, func(f *flac.File, cmt *flacvorbis.MetaDataBlockVorbisComment) error {
+		writeVorbisMetadata(cmt, metadata)
 
-	for idx, meta := range f.Meta {
-		if meta.Type == flac.VorbisComment {
-			cmtIdx = idx
-			cmt, err = flacvorbis.ParseFromMetaDataBlock(*meta)
-			if err != nil {
-				return fmt.Errorf("failed to parse vorbis comment: %w", err)
-			}
-			break
-		}
-	}
-
-	if cmt == nil {
-		cmt = flacvorbis.New()
-	}
-
-	writeVorbisMetadata(cmt, metadata)
-
-	cmtBlock := cmt.Marshal()
-	if cmtIdx >= 0 {
-		f.Meta[cmtIdx] = &cmtBlock
-	} else {
-		f.Meta = append(f.Meta, &cmtBlock)
-	}
-
-	if len(coverData) > 0 {
-		for i := len(f.Meta) - 1; i >= 0; i-- {
-			if f.Meta[i].Type == flac.Picture {
-				f.Meta = append(f.Meta[:i], f.Meta[i+1:]...)
+		if coverPath != "" {
+			if fileExists(coverPath) {
+				coverData, err := os.ReadFile(coverPath)
+				if err != nil {
+					fmt.Printf("[Metadata] Warning: Failed to read cover file %s: %v\n", coverPath, err)
+				} else if err := replaceFlacPictures(f, coverPath, coverData); err != nil {
+					fmt.Printf("[Metadata] Warning: skipping cover art: %v\n", err)
+				} else {
+					fmt.Printf("[Metadata] Cover art embedded successfully (%d bytes)\n", len(coverData))
+				}
+			} else {
+				fmt.Printf("[Metadata] Warning: Cover file does not exist: %s\n", coverPath)
 			}
 		}
+		return nil
+	})
+}
 
-		picBlock, err := buildPictureBlock("", coverData)
-		if err != nil {
-			fmt.Printf("[Metadata] Warning: skipping cover art: %v\n", err)
-		} else {
-			f.Meta = append(f.Meta, &picBlock)
-			fmt.Printf("[Metadata] Cover art embedded successfully (%d bytes)\n", len(coverData))
+func EmbedMetadataWithCoverData(filePath string, metadata Metadata, coverData []byte) error {
+	return updateFlacVorbis(filePath, func(f *flac.File, cmt *flacvorbis.MetaDataBlockVorbisComment) error {
+		writeVorbisMetadata(cmt, metadata)
+
+		if len(coverData) > 0 {
+			if err := replaceFlacPictures(f, "", coverData); err != nil {
+				fmt.Printf("[Metadata] Warning: skipping cover art: %v\n", err)
+			} else {
+				fmt.Printf("[Metadata] Cover art embedded successfully (%d bytes)\n", len(coverData))
+			}
 		}
-	}
-
-	return saveFlacFile(f, filePath)
+		return nil
+	})
 }
 
 func ReadMetadata(filePath string) (*Metadata, error) {
@@ -424,55 +408,17 @@ func ReadMetadata(filePath string) (*Metadata, error) {
 // absent from the map are left untouched.  This is the correct function for
 // partial edits (e.g. writing only ReplayGain tags) and full editor saves alike.
 func EditFlacFields(filePath string, fields map[string]string) error {
-	f, err := parseFlacFile(filePath)
-	if err != nil {
-		return fmt.Errorf("failed to parse FLAC file: %w", err)
-	}
-	defer f.Close()
+	return updateFlacVorbis(filePath, func(f *flac.File, cmt *flacvorbis.MetaDataBlockVorbisComment) error {
+		applyVorbisFieldEdits(cmt, fields)
 
-	var cmtIdx int = -1
-	var cmt *flacvorbis.MetaDataBlockVorbisComment
-
-	for idx, meta := range f.Meta {
-		if meta.Type == flac.VorbisComment {
-			cmtIdx = idx
-			cmt, err = flacvorbis.ParseFromMetaDataBlock(*meta)
-			if err != nil {
-				return fmt.Errorf("failed to parse vorbis comment: %w", err)
-			}
-			break
-		}
-	}
-	if cmt == nil {
-		cmt = flacvorbis.New()
-	}
-
-	applyVorbisFieldEdits(cmt, fields)
-
-	cmtBlock := cmt.Marshal()
-	if cmtIdx >= 0 {
-		f.Meta[cmtIdx] = &cmtBlock
-	} else {
-		f.Meta = append(f.Meta, &cmtBlock)
-	}
-
-	coverPath := strings.TrimSpace(fields["cover_path"])
-	if coverPath != "" && fileExists(coverPath) {
-		coverData, err := os.ReadFile(coverPath)
-		if err == nil && len(coverData) > 0 {
-			for i := len(f.Meta) - 1; i >= 0; i-- {
-				if f.Meta[i].Type == flac.Picture {
-					f.Meta = append(f.Meta[:i], f.Meta[i+1:]...)
-				}
-			}
-			picBlock, err := buildPictureBlock("", coverData)
-			if err == nil {
-				f.Meta = append(f.Meta, &picBlock)
+		coverPath := strings.TrimSpace(fields["cover_path"])
+		if coverPath != "" && fileExists(coverPath) {
+			if coverData, err := os.ReadFile(coverPath); err == nil && len(coverData) > 0 {
+				_ = replaceFlacPictures(f, "", coverData)
 			}
 		}
-	}
-
-	return saveFlacFile(f, filePath)
+		return nil
+	})
 }
 
 // applyVorbisFieldEdits applies the editor's set-or-clear field semantics to a
@@ -711,45 +657,11 @@ func setOrClearArtistComments(cmt *flacvorbis.MetaDataBlockVorbisComment, key, v
 // the last value survives when multiple -metadata ARTIST=X flags are used.
 // The native go-flac writer correctly handles multiple Vorbis comments.
 func RewriteSplitArtistTags(filePath, artist, albumArtist string) error {
-	if !shouldSplitVorbisArtistTags(artistTagModeSplitVorbis) {
+	return updateFlacVorbis(filePath, func(_ *flac.File, cmt *flacvorbis.MetaDataBlockVorbisComment) error {
+		setArtistComments(cmt, "ARTIST", artist, artistTagModeSplitVorbis)
+		setArtistComments(cmt, "ALBUMARTIST", albumArtist, artistTagModeSplitVorbis)
 		return nil
-	}
-
-	f, err := parseFlacFile(filePath)
-	if err != nil {
-		return fmt.Errorf("failed to parse FLAC file: %w", err)
-	}
-	defer f.Close()
-
-	var cmtIdx int = -1
-	var cmt *flacvorbis.MetaDataBlockVorbisComment
-
-	for idx, meta := range f.Meta {
-		if meta.Type == flac.VorbisComment {
-			cmtIdx = idx
-			cmt, err = flacvorbis.ParseFromMetaDataBlock(*meta)
-			if err != nil {
-				return fmt.Errorf("failed to parse vorbis comment: %w", err)
-			}
-			break
-		}
-	}
-
-	if cmt == nil {
-		cmt = flacvorbis.New()
-	}
-
-	setArtistComments(cmt, "ARTIST", artist, artistTagModeSplitVorbis)
-	setArtistComments(cmt, "ALBUMARTIST", albumArtist, artistTagModeSplitVorbis)
-
-	cmtMeta := cmt.Marshal()
-	if cmtIdx >= 0 {
-		f.Meta[cmtIdx] = &cmtMeta
-	} else {
-		f.Meta = append(f.Meta, &cmtMeta)
-	}
-
-	return saveFlacFile(f, filePath)
+	})
 }
 
 func removeCommentKey(cmt *flacvorbis.MetaDataBlockVorbisComment, key string) {
@@ -884,87 +796,11 @@ func ExtractCoverArt(filePath string) ([]byte, error) {
 }
 
 func EmbedLyrics(filePath string, lyrics string) error {
-	f, err := parseFlacFile(filePath)
-	if err != nil {
-		return fmt.Errorf("failed to parse FLAC file: %w", err)
-	}
-	defer f.Close()
-
-	var cmtIdx int = -1
-	var cmt *flacvorbis.MetaDataBlockVorbisComment
-
-	for idx, meta := range f.Meta {
-		if meta.Type == flac.VorbisComment {
-			cmtIdx = idx
-			cmt, err = flacvorbis.ParseFromMetaDataBlock(*meta)
-			if err != nil {
-				return fmt.Errorf("failed to parse vorbis comment: %w", err)
-			}
-			break
-		}
-	}
-
-	if cmt == nil {
-		cmt = flacvorbis.New()
-	}
-
-	setComment(cmt, "LYRICS", lyrics)
-	setComment(cmt, "UNSYNCEDLYRICS", lyrics)
-
-	cmtBlock := cmt.Marshal()
-	if cmtIdx >= 0 {
-		f.Meta[cmtIdx] = &cmtBlock
-	} else {
-		f.Meta = append(f.Meta, &cmtBlock)
-	}
-
-	return saveFlacFile(f, filePath)
-}
-
-func EmbedGenreLabel(filePath string, genre, label string) error {
-	if genre == "" && label == "" {
+	return updateFlacVorbis(filePath, func(_ *flac.File, cmt *flacvorbis.MetaDataBlockVorbisComment) error {
+		setComment(cmt, "LYRICS", lyrics)
+		setComment(cmt, "UNSYNCEDLYRICS", lyrics)
 		return nil
-	}
-
-	f, err := parseFlacFile(filePath)
-	if err != nil {
-		return fmt.Errorf("failed to parse FLAC file: %w", err)
-	}
-	defer f.Close()
-
-	var cmtIdx int = -1
-	var cmt *flacvorbis.MetaDataBlockVorbisComment
-
-	for idx, meta := range f.Meta {
-		if meta.Type == flac.VorbisComment {
-			cmtIdx = idx
-			cmt, err = flacvorbis.ParseFromMetaDataBlock(*meta)
-			if err != nil {
-				return fmt.Errorf("failed to parse vorbis comment: %w", err)
-			}
-			break
-		}
-	}
-
-	if cmt == nil {
-		cmt = flacvorbis.New()
-	}
-
-	if genre != "" {
-		setComment(cmt, "GENRE", genre)
-	}
-	if label != "" {
-		setComment(cmt, "ORGANIZATION", label)
-	}
-
-	cmtBlock := cmt.Marshal()
-	if cmtIdx >= 0 {
-		f.Meta[cmtIdx] = &cmtBlock
-	} else {
-		f.Meta = append(f.Meta, &cmtBlock)
-	}
-
-	return saveFlacFile(f, filePath)
+	})
 }
 
 func ExtractLyrics(filePath string) (string, error) {
diff --git a/go_backend/misc_coverage_supplement_test.go b/go_backend/misc_coverage_supplement_test.go
index 75e53cb5..b187f163 100644
--- a/go_backend/misc_coverage_supplement_test.go
+++ b/go_backend/misc_coverage_supplement_test.go
@@ -89,7 +89,6 @@ func TestMoreSmallConstructorsRuntimeAndMetadataHelpers(t *testing.T) {
 	if NewIDHSClient().client == nil {
 		t.Fatal("expected IDHS HTTP client")
 	}
-	ClearTrackCache()
 
 	vm := goja.New()
 	runtime := &extensionRuntime{extensionID: "misc-runtime", vm: vm, settings: map[string]any{}}
@@ -159,15 +158,6 @@ func TestMoreSmallConstructorsRuntimeAndMetadataHelpers(t *testing.T) {
 	if string(mustReadFile(t, coverPath)) != "cover" {
 		t.Fatal("downloaded cover mismatch")
 	}
-
-	parallel := FetchCoverAndLyricsParallel(server.URL+"/cover.jpg", false, "spotify-1", "Song Instrumental", "Artist", true, 180000)
-	if string(parallel.CoverData) != "cover" || parallel.CoverErr != nil || parallel.LyricsErr == nil {
-		t.Fatalf("FetchCoverAndLyricsParallel = %#v", parallel)
-	}
-	emptyParallel := FetchCoverAndLyricsParallel("", false, "", "", "", false, 0)
-	if emptyParallel.CoverData != nil || emptyParallel.LyricsData != nil {
-		t.Fatalf("empty FetchCoverAndLyricsParallel = %#v", emptyParallel)
-	}
 }
 
 func TestExtensionHealthInitializeVMAndCustomSearchWrappers(t *testing.T) {
diff --git a/go_backend/parallel.go b/go_backend/parallel.go
deleted file mode 100644
index 611b971d..00000000
--- a/go_backend/parallel.go
+++ /dev/null
@@ -1,114 +0,0 @@
-package gobackend
-
-import (
-	"encoding/json"
-	"fmt"
-	"sync"
-)
-
-type ParallelDownloadResult struct {
-	CoverData  []byte
-	LyricsData *LyricsResponse
-	LyricsLRC  string
-	CoverErr   error
-	LyricsErr  error
-}
-
-func FetchCoverAndLyricsParallel(
-	coverURL string,
-	maxQualityCover bool,
-	spotifyID string,
-	trackName string,
-	artistName string,
-	embedLyrics bool,
-	durationMs int64,
-) *ParallelDownloadResult {
-	result := &ParallelDownloadResult{}
-	var wg sync.WaitGroup
-	var resultMu sync.Mutex
-
-	if coverURL != "" {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			data, err := downloadCoverToMemory(coverURL, maxQualityCover)
-			resultMu.Lock()
-			if err != nil {
-				result.CoverErr = err
-			} else {
-				result.CoverData = data
-			}
-			resultMu.Unlock()
-		}()
-	}
-
-	if embedLyrics {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			client := NewLyricsClient()
-			durationSec := float64(durationMs) / 1000.0
-			lyrics, err := client.FetchLyricsAllSources(spotifyID, trackName, artistName, durationSec)
-			resultMu.Lock()
-			if err != nil {
-				result.LyricsErr = err
-			} else if lyrics != nil && len(lyrics.Lines) > 0 {
-				result.LyricsData = lyrics
-				result.LyricsLRC = convertToLRCWithMetadata(lyrics, trackName, artistName)
-			} else {
-				result.LyricsErr = fmt.Errorf("no lyrics found")
-			}
-			resultMu.Unlock()
-		}()
-	}
-
-	wg.Wait()
-	return result
-}
-
-type PreWarmCacheRequest struct {
-	ISRC       string
-	TrackName  string
-	ArtistName string
-	SpotifyID  string
-	Service    string
-}
-
-func PreWarmTrackCache(requests []PreWarmCacheRequest) {
-	_ = requests
-}
-
-func PreWarmCache(tracksJSON string) error {
-	var tracks []struct {
-		ISRC       string `json:"isrc"`
-		TrackName  string `json:"track_name"`
-		ArtistName string `json:"artist_name"`
-		SpotifyID  string `json:"spotify_id"`
-		Service    string `json:"service"`
-	}
-
-	if err := json.Unmarshal([]byte(tracksJSON), &tracks); err != nil {
-		return fmt.Errorf("failed to parse tracks JSON: %w", err)
-	}
-
-	requests := make([]PreWarmCacheRequest, len(tracks))
-	for i, t := range tracks {
-		requests[i] = PreWarmCacheRequest{
-			ISRC:       t.ISRC,
-			TrackName:  t.TrackName,
-			ArtistName: t.ArtistName,
-			SpotifyID:  t.SpotifyID,
-			Service:    t.Service,
-		}
-	}
-
-	go PreWarmTrackCache(requests)
-	return nil
-}
-
-func ClearTrackCache() {
-}
-
-func GetCacheSize() int {
-	return 0
-}
diff --git a/go_backend/progress.go b/go_backend/progress.go
index 4abcd5b4..b697828c 100644
--- a/go_backend/progress.go
+++ b/go_backend/progress.go
@@ -193,17 +193,6 @@ func GetMultiProgressDelta(sinceSeq int64) string {
 	return string(jsonBytes)
 }
 
-func GetItemProgress(itemID string) string {
-	multiMu.RLock()
-	defer multiMu.RUnlock()
-
-	if item, ok := multiProgress.Items[itemID]; ok {
-		jsonBytes, _ := json.Marshal(item)
-		return string(jsonBytes)
-	}
-	return "{}"
-}
-
 func StartItemProgress(itemID string) {
 	multiMu.Lock()
 	defer multiMu.Unlock()
@@ -359,6 +348,17 @@ func RemoveItemProgress(itemID string) {
 	markMultiProgressDirtyLocked()
 }
 
+func GetItemProgress(itemID string) string {
+	multiMu.RLock()
+	defer multiMu.RUnlock()
+
+	if item, ok := multiProgress.Items[itemID]; ok {
+		jsonBytes, _ := json.Marshal(item)
+		return string(jsonBytes)
+	}
+	return "{}"
+}
+
 func ClearAllItemProgress() {
 	multiMu.Lock()
 	defer multiMu.Unlock()
diff --git a/go_backend/ratelimit.go b/go_backend/ratelimit.go
index 662d86e4..91078c86 100644
--- a/go_backend/ratelimit.go
+++ b/go_backend/ratelimit.go
@@ -90,7 +90,3 @@ func (r *RateLimiter) Available() int {
 
 // Global SongLink rate limiter - 9 requests per minute (to be safe, limit is 10)
 var songLinkRateLimiter = NewRateLimiter(9, time.Minute)
-
-func GetSongLinkRateLimiter() *RateLimiter {
-	return songLinkRateLimiter
-}
diff --git a/go_backend/romaji.go b/go_backend/romaji.go
deleted file mode 100644
index fce9524a..00000000
--- a/go_backend/romaji.go
+++ /dev/null
@@ -1,193 +0,0 @@
-package gobackend
-
-import (
-	"strings"
-	"unicode"
-)
-
-var hiraganaToRomaji = map[rune]string{
-	'あ': "a", 'い': "i", 'う': "u", 'え': "e", 'お': "o",
-	'か': "ka", 'き': "ki", 'く': "ku", 'け': "ke", 'こ': "ko",
-	'さ': "sa", 'し': "shi", 'す': "su", 'せ': "se", 'そ': "so",
-	'た': "ta", 'ち': "chi", 'つ': "tsu", 'て': "te", 'と': "to",
-	'な': "na", 'に': "ni", 'ぬ': "nu", 'ね': "ne", 'の': "no",
-	'は': "ha", 'ひ': "hi", 'ふ': "fu", 'へ': "he", 'ほ': "ho",
-	'ま': "ma", 'み': "mi", 'む': "mu", 'め': "me", 'も': "mo",
-	'や': "ya", 'ゆ': "yu", 'よ': "yo",
-	'ら': "ra", 'り': "ri", 'る': "ru", 'れ': "re", 'ろ': "ro",
-	'わ': "wa", 'を': "wo", 'ん': "n",
-	'が': "ga", 'ぎ': "gi", 'ぐ': "gu", 'げ': "ge", 'ご': "go",
-	'ざ': "za", 'じ': "ji", 'ず': "zu", 'ぜ': "ze", 'ぞ': "zo",
-	'だ': "da", 'ぢ': "ji", 'づ': "zu", 'で': "de", 'ど': "do",
-	'ば': "ba", 'び': "bi", 'ぶ': "bu", 'べ': "be", 'ぼ': "bo",
-	'ぱ': "pa", 'ぴ': "pi", 'ぷ': "pu", 'ぺ': "pe", 'ぽ': "po",
-	'ゃ': "ya", 'ゅ': "yu", 'ょ': "yo",
-	'っ': "",
-	'ぁ': "a", 'ぃ': "i", 'ぅ': "u", 'ぇ': "e", 'ぉ': "o",
-}
-
-var katakanaToRomaji = map[rune]string{
-	'ア': "a", 'イ': "i", 'ウ': "u", 'エ': "e", 'オ': "o",
-	'カ': "ka", 'キ': "ki", 'ク': "ku", 'ケ': "ke", 'コ': "ko",
-	'サ': "sa", 'シ': "shi", 'ス': "su", 'セ': "se", 'ソ': "so",
-	'タ': "ta", 'チ': "chi", 'ツ': "tsu", 'テ': "te", 'ト': "to",
-	'ナ': "na", 'ニ': "ni", 'ヌ': "nu", 'ネ': "ne", 'ノ': "no",
-	'ハ': "ha", 'ヒ': "hi", 'フ': "fu", 'ヘ': "he", 'ホ': "ho",
-	'マ': "ma", 'ミ': "mi", 'ム': "mu", 'メ': "me", 'モ': "mo",
-	'ヤ': "ya", 'ユ': "yu", 'ヨ': "yo",
-	'ラ': "ra", 'リ': "ri", 'ル': "ru", 'レ': "re", 'ロ': "ro",
-	'ワ': "wa", 'ヲ': "wo", 'ン': "n",
-	'ガ': "ga", 'ギ': "gi", 'グ': "gu", 'ゲ': "ge", 'ゴ': "go",
-	'ザ': "za", 'ジ': "ji", 'ズ': "zu", 'ゼ': "ze", 'ゾ': "zo",
-	'ダ': "da", 'ヂ': "ji", 'ヅ': "zu", 'デ': "de", 'ド': "do",
-	'バ': "ba", 'ビ': "bi", 'ブ': "bu", 'ベ': "be", 'ボ': "bo",
-	'パ': "pa", 'ピ': "pi", 'プ': "pu", 'ペ': "pe", 'ポ': "po",
-	'ャ': "ya", 'ュ': "yu", 'ョ': "yo",
-	'ッ': "",
-	'ァ': "a", 'ィ': "i", 'ゥ': "u", 'ェ': "e", 'ォ': "o",
-	'ー': "",
-	'ヴ': "vu",
-}
-
-var combinationHiragana = map[string]string{
-	"きゃ": "kya", "きゅ": "kyu", "きょ": "kyo",
-	"しゃ": "sha", "しゅ": "shu", "しょ": "sho",
-	"ちゃ": "cha", "ちゅ": "chu", "ちょ": "cho",
-	"にゃ": "nya", "にゅ": "nyu", "にょ": "nyo",
-	"ひゃ": "hya", "ひゅ": "hyu", "ひょ": "hyo",
-	"みゃ": "mya", "みゅ": "myu", "みょ": "myo",
-	"りゃ": "rya", "りゅ": "ryu", "りょ": "ryo",
-	"ぎゃ": "gya", "ぎゅ": "gyu", "ぎょ": "gyo",
-	"じゃ": "ja", "じゅ": "ju", "じょ": "jo",
-	"びゃ": "bya", "びゅ": "byu", "びょ": "byo",
-	"ぴゃ": "pya", "ぴゅ": "pyu", "ぴょ": "pyo",
-}
-
-var combinationKatakana = map[string]string{
-	"キャ": "kya", "キュ": "kyu", "キョ": "kyo",
-	"シャ": "sha", "シュ": "shu", "ショ": "sho",
-	"チャ": "cha", "チュ": "chu", "チョ": "cho",
-	"ニャ": "nya", "ニュ": "nyu", "ニョ": "nyo",
-	"ヒャ": "hya", "ヒュ": "hyu", "ヒョ": "hyo",
-	"ミャ": "mya", "ミュ": "myu", "ミョ": "myo",
-	"リャ": "rya", "リュ": "ryu", "リョ": "ryo",
-	"ギャ": "gya", "ギュ": "gyu", "ギョ": "gyo",
-	"ジャ": "ja", "ジュ": "ju", "ジョ": "jo",
-	"ビャ": "bya", "ビュ": "byu", "ビョ": "byo",
-	"ピャ": "pya", "ピュ": "pyu", "ピョ": "pyo",
-	"ティ": "ti", "ディ": "di", "トゥ": "tu", "ドゥ": "du",
-	"ファ": "fa", "フィ": "fi", "フェ": "fe", "フォ": "fo",
-	"ウィ": "wi", "ウェ": "we", "ウォ": "wo",
-}
-
-func ContainsJapanese(s string) bool {
-	for _, r := range s {
-		if isHiragana(r) || isKatakana(r) || isKanji(r) {
-			return true
-		}
-	}
-	return false
-}
-
-func isHiragana(r rune) bool {
-	return r >= 0x3040 && r <= 0x309F
-}
-
-func isKatakana(r rune) bool {
-	return r >= 0x30A0 && r <= 0x30FF
-}
-
-func isKanji(r rune) bool {
-	return (r >= 0x4E00 && r <= 0x9FFF) || // CJK Unified Ideographs
-		(r >= 0x3400 && r <= 0x4DBF) // CJK Unified Ideographs Extension A
-}
-
-func JapaneseToRomaji(text string) string {
-	if !ContainsJapanese(text) {
-		return text
-	}
-
-	var result strings.Builder
-	runes := []rune(text)
-	i := 0
-
-	for i < len(runes) {
-		if i < len(runes)-1 && (runes[i] == 'っ' || runes[i] == 'ッ') {
-			nextRomaji := ""
-			if romaji, ok := hiraganaToRomaji[runes[i+1]]; ok {
-				nextRomaji = romaji
-			} else if romaji, ok := katakanaToRomaji[runes[i+1]]; ok {
-				nextRomaji = romaji
-			}
-			if len(nextRomaji) > 0 {
-				result.WriteByte(nextRomaji[0])
-			}
-			i++
-			continue
-		}
-
-		if i < len(runes)-1 {
-			combo := string(runes[i : i+2])
-			if romaji, ok := combinationHiragana[combo]; ok {
-				result.WriteString(romaji)
-				i += 2
-				continue
-			}
-			if romaji, ok := combinationKatakana[combo]; ok {
-				result.WriteString(romaji)
-				i += 2
-				continue
-			}
-		}
-
-		r := runes[i]
-		if romaji, ok := hiraganaToRomaji[r]; ok {
-			result.WriteString(romaji)
-		} else if romaji, ok := katakanaToRomaji[r]; ok {
-			result.WriteString(romaji)
-		} else if isKanji(r) {
-			result.WriteRune(r)
-		} else {
-			result.WriteRune(r)
-		}
-		i++
-	}
-
-	return result.String()
-}
-
-func BuildSearchQuery(trackName, artistName string) string {
-	trackRomaji := JapaneseToRomaji(trackName)
-	artistRomaji := JapaneseToRomaji(artistName)
-
-	trackClean := cleanSearchQuery(trackRomaji)
-	artistClean := cleanSearchQuery(artistRomaji)
-
-	return strings.TrimSpace(artistClean + " " + trackClean)
-}
-
-func cleanSearchQuery(s string) string {
-	var result strings.Builder
-	for _, r := range s {
-		if unicode.IsLetter(r) || unicode.IsNumber(r) || unicode.IsSpace(r) {
-			result.WriteRune(r)
-		} else if r == '-' || r == '\'' {
-			result.WriteRune(r)
-		}
-	}
-	return strings.TrimSpace(result.String())
-}
-
-func CleanToASCII(s string) string {
-	var result strings.Builder
-	for _, r := range s {
-		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') ||
-			(r >= '0' && r <= '9') || r == ' ' || r == '-' || r == '\'' {
-			result.WriteRune(r)
-		} else if r == ',' || r == '.' {
-			result.WriteRune(' ')
-		}
-	}
-	cleaned := strings.Join(strings.Fields(result.String()), " ")
-	return strings.TrimSpace(cleaned)
-}
diff --git a/ios/Runner/AppDelegate.swift b/ios/Runner/AppDelegate.swift
index 7526ee34..d56d22b9 100644
--- a/ios/Runner/AppDelegate.swift
+++ b/ios/Runner/AppDelegate.swift
@@ -447,14 +447,6 @@ import Gobackend
         var error: NSError?
         
         switch call.method {
-        case "checkAvailability":
-            let args = call.arguments as! [String: Any]
-            let spotifyId = args["spotify_id"] as! String
-            let isrc = args["isrc"] as! String
-            let response = GobackendCheckAvailability(spotifyId, isrc, &error)
-            if let error = error { throw error }
-            return response
-            
         case "downloadByStrategy":
             let requestJson = call.arguments as! String
             let response = GobackendDownloadByStrategy(requestJson, &error)
@@ -706,22 +698,6 @@ import Gobackend
             if let error = error { throw error }
             return response
 
-        case "checkAvailabilityFromDeezerID":
-            let args = call.arguments as! [String: Any]
-            let deezerTrackId = args["deezer_track_id"] as! String
-            let response = GobackendCheckAvailabilityFromDeezerID(deezerTrackId, &error)
-            if let error = error { throw error }
-            return response
-            
-        case "checkAvailabilityByPlatformID":
-            let args = call.arguments as! [String: Any]
-            let platform = args["platform"] as! String
-            let entityType = args["entity_type"] as! String
-            let entityId = args["entity_id"] as! String
-            let response = GobackendCheckAvailabilityByPlatformID(platform, entityType, entityId, &error)
-            if let error = error { throw error }
-            return response
-            
         case "getSpotifyIDFromDeezerTrack":
             let args = call.arguments as! [String: Any]
             let deezerTrackId = args["deezer_track_id"] as! String
@@ -736,19 +712,12 @@ import Gobackend
             if let error = error { throw error }
             return response
             
-        case "preWarmTrackCache":
-            let args = call.arguments as! [String: Any]
-            let tracksJson = args["tracks"] as! String
-            let _ = GobackendPreWarmTrackCacheJSON(tracksJson, &error)
-            if let error = error { throw error }
-            return nil
-            
         case "getTrackCacheSize":
             let response = GobackendGetTrackCacheSize()
             return response
             
         case "clearTrackCache":
-            GobackendClearTrackCache()
+            GobackendClearTrackIDCache()
             return nil
             
         case "getLogs":
diff --git a/lib/providers/track_provider.dart b/lib/providers/track_provider.dart
index d93f9a13..16a670d8 100644
--- a/lib/providers/track_provider.dart
+++ b/lib/providers/track_provider.dart
@@ -674,34 +674,6 @@ class TrackNotifier extends Notifier<TrackState> {
     }
   }
 
-  Future<void> checkAvailability(int index) async {
-    if (index < 0 || index >= state.tracks.length) return;
-
-    final track = state.tracks[index];
-    if (track.isrc == null || track.isrc!.isEmpty) return;
-
-    try {
-      final availability = await PlatformBridge.checkAvailability(
-        track.id,
-        track.isrc!,
-      );
-      final updatedTrack = track.copyWith(
-        availability: ServiceAvailability(
-          tidal: availability['tidal'] as bool? ?? false,
-          qobuz: availability['qobuz'] as bool? ?? false,
-          amazon: availability['amazon'] as bool? ?? false,
-          tidalUrl: availability['tidal_url'] as String?,
-          qobuzUrl: availability['qobuz_url'] as String?,
-          amazonUrl: availability['amazon_url'] as String?,
-        ),
-      );
-
-      final tracks = List<Track>.from(state.tracks);
-      tracks[index] = updatedTrack;
-      state = state.copyWith(tracks: tracks);
-    } catch (_) {}
-  }
-
   void clear() {
     state = const TrackState();
   }
diff --git a/lib/services/platform_bridge.dart b/lib/services/platform_bridge.dart
index 110d72ac..c512311c 100644
--- a/lib/services/platform_bridge.dart
+++ b/lib/services/platform_bridge.dart
@@ -66,13 +66,10 @@ class PlatformBridge {
   static const _jsonResultFileKey = '__json_file';
   static const _backgroundJsonDecodeThresholdBytes = 128 * 1024;
   static const _metadataCacheTtl = Duration(minutes: 20);
-  static const _availabilityCacheTtl = Duration(minutes: 15);
   static const _urlHandleCacheTtl = Duration(minutes: 5);
   static const _customSearchCacheTtl = Duration(minutes: 2);
   static const _bridgeCacheMaxEntries = 256;
   static const _metadataPersistentCacheKey = 'bridge_metadata_lookup_cache_v1';
-  static const _availabilityPersistentCacheKey =
-      'bridge_availability_lookup_cache_v1';
   static const _downloadProgressEvents = EventChannel(
     'com.zarz.spotiflac/download_progress_stream',
   );
@@ -80,12 +77,9 @@ class PlatformBridge {
     'com.zarz.spotiflac/library_scan_progress_stream',
   );
   static final Map<String, _BridgeCacheEntry> _metadataCache = {};
-  static final Map<String, _BridgeCacheEntry> _availabilityCache = {};
   static final Map<String, _BridgeCacheEntry> _urlHandleCache = {};
   static final Map<String, _BridgeListCacheEntry> _customSearchCache = {};
   static final Map<String, Future<Map<String, dynamic>>> _metadataInFlight = {};
-  static final Map<String, Future<Map<String, dynamic>>> _availabilityInFlight =
-      {};
   static final Map<String, Future<Map<String, dynamic>?>> _urlHandleInFlight =
       {};
   static final Map<String, _BridgeInFlight<List<Map<String, dynamic>>>>
@@ -135,30 +129,6 @@ class PlatformBridge {
     });
   }
 
-  static Future<Map<String, dynamic>> checkAvailability(
-    String spotifyId,
-    String isrc,
-  ) {
-    Future<Map<String, dynamic>> load() {
-      _log.d('checkAvailability: $spotifyId (ISRC: $isrc)');
-      return _invokeMap('checkAvailability', {
-        'spotify_id': spotifyId,
-        'isrc': isrc,
-      });
-    }
-
-    final cacheKey = _availabilityCacheKey(spotifyId, isrc);
-    if (cacheKey.isEmpty) return load();
-    return _cachedInvoke(
-      cacheKey,
-      _availabilityCache,
-      _availabilityInFlight,
-      _availabilityCacheTtl,
-      _availabilityPersistentCacheKey,
-      load,
-    );
-  }
-
   static Future<Map<String, dynamic>> _invokeMap(
     String method, [
     dynamic args,
@@ -198,16 +168,6 @@ class PlatformBridge {
     }
   }
 
-  static String _availabilityCacheKey(String spotifyId, String isrc) {
-    final normalizedIsrc = isrc.trim().toUpperCase();
-    if (normalizedIsrc.isNotEmpty) {
-      return 'isrc:$normalizedIsrc';
-    }
-    final normalizedSpotifyId = spotifyId.trim();
-    if (normalizedSpotifyId.isEmpty) return '';
-    return 'spotify:$normalizedSpotifyId';
-  }
-
   static String _providerMetadataCacheKey(
     String providerId,
     String resourceType,
@@ -322,11 +282,6 @@ class PlatformBridge {
         _metadataPersistentCacheKey,
         _metadataCache,
       );
-      _restorePersistentCache(
-        prefs,
-        _availabilityPersistentCacheKey,
-        _availabilityCache,
-      );
     } catch (e) {
       _log.w('Failed to load bridge lookup cache: $e');
     }
@@ -390,7 +345,8 @@ class PlatformBridge {
     try {
       final prefs = await SharedPreferences.getInstance();
       await prefs.remove(_metadataPersistentCacheKey);
-      await prefs.remove(_availabilityPersistentCacheKey);
+      // Legacy key from the removed availability-check feature.
+      await prefs.remove('bridge_availability_lookup_cache_v1');
     } catch (e) {
       _log.w('Failed to clear bridge lookup cache: $e');
     }
@@ -400,11 +356,9 @@ class PlatformBridge {
     _lookupCacheGeneration++;
     _persistentLookupCacheLoadFuture = null;
     _metadataCache.clear();
-    _availabilityCache.clear();
     _urlHandleCache.clear();
     _customSearchCache.clear();
     _metadataInFlight.clear();
-    _availabilityInFlight.clear();
     _urlHandleInFlight.clear();
     for (final inFlight in _customSearchInFlight.values) {
       _cancelExtensionRequestUnawaited(inFlight.requestId);
@@ -462,8 +416,7 @@ class PlatformBridge {
 
   static int _lookupCacheSize() {
     _pruneExpiredBridgeCache(_metadataCache);
-    _pruneExpiredBridgeCache(_availabilityCache);
-    return _metadataCache.length + _availabilityCache.length;
+    return _metadataCache.length;
   }
 
   static Future<Map<String, dynamic>> _invokeDownloadMethod(
@@ -1081,13 +1034,6 @@ class PlatformBridge {
     return _decodeMapResult(result);
   }
 
-  static Future<void> preWarmTrackCache(
-    List<Map<String, String>> tracks,
-  ) async {
-    final tracksJson = jsonEncode(tracks);
-    await _channel.invokeMethod('preWarmTrackCache', {'tracks': tracksJson});
-  }
-
   static Future<int> getTrackCacheSize() async {
     await _ensurePersistentLookupCachesLoaded();
     final result = await _channel.invokeMethod('getTrackCacheSize');