perf(android): sweep stale cache files, relax scan poll, debounce worker snapshots

android/app/src/main/kotlin/com/zarz/spotiflac/DownloadService.kt

@@ -718,15 +718,29 @@ class DownloadService : Service() {
                 try {
                     Gobackend.initItemProgress(request.itemId)
                     progressJob = serviceScope.launch {
+                        // The snapshot write is an AtomicFile open+fsync+
+                        // rename; skip ticks where progress hasn't moved.
+                        var lastSignature: String? = null
                         while (true) {
                             updateNativeWorkerItemProgress(request.itemId)
-                            writeNativeWorkerSnapshot(
-                                isRunning = true,
-                                isPaused = false,
-                                currentItemId = request.itemId,
-                                message = "Downloading",
-                                settingsJson = settingsJson
-                            )
+                            val signature = synchronized(nativeWorkerItems) {
+                                nativeWorkerItems
+                                    .firstOrNull { it.itemId == request.itemId }
+                                    ?.let {
+                                        "${it.status}:${it.bytesReceived}:" +
+                                            "${it.bytesTotal}:${it.progress}"
+                                    }
+                            }
+                            if (signature != lastSignature) {
+                                lastSignature = signature
+                                writeNativeWorkerSnapshot(
+                                    isRunning = true,
+                                    isPaused = false,
+                                    currentItemId = request.itemId,
+                                    message = "Downloading",
+                                    settingsJson = settingsJson
+                                )
+                            }
                             delay(1000)
                         }
                     }

android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt

@@ -62,7 +62,9 @@ class MainActivity: FlutterFragmentActivity() {
     private val LIBRARY_SCAN_PROGRESS_STREAM_CHANNEL =
         "com.zarz.spotiflac/library_scan_progress_stream"
     private val DOWNLOAD_PROGRESS_STREAM_POLLING_INTERVAL_MS = 1200L
-    private val LIBRARY_SCAN_PROGRESS_STREAM_POLLING_INTERVAL_MS = 200L
+    // A progress bar can't show sub-second granularity; 400ms halves the
+    // disk-read wakeups during a scan vs the previous 200ms.
+    private val LIBRARY_SCAN_PROGRESS_STREAM_POLLING_INTERVAL_MS = 400L
     private val LARGE_JSON_RESULT_FILE_KEY = "__json_file"
     private val LARGE_JSON_RESULT_FILE_THRESHOLD_BYTES = 256 * 1024
     private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Main)
@@ -1957,6 +1959,27 @@ class MainActivity: FlutterFragmentActivity() {
     // We handle these URLs ourselves via receive_sharing_intent + ShareIntentService.
     override fun shouldHandleDeeplinking(): Boolean = false
 
+    // Bridge spill files and SAF temp copies are deleted after use on the
+    // normal path, but a process kill mid-operation orphans them in cacheDir
+    // forever (names embed nanoTime, so nothing overwrites them). Sweep
+    // leftovers from previous sessions; the 1h age guard protects in-flight
+    // files from concurrent work in this session.
+    private fun sweepStaleCacheFiles() {
+        scope.launch(Dispatchers.IO) {
+            try {
+                val cutoff = System.currentTimeMillis() - 60 * 60 * 1000L
+                cacheDir.listFiles()?.forEach { file ->
+                    val stale = file.isFile &&
+                        file.lastModified() < cutoff &&
+                        (file.name.startsWith("bridge_json_") ||
+                            file.name.startsWith("saf_") ||
+                            file.name.startsWith("ms_"))
+                    if (stale) file.delete()
+                }
+            } catch (_: Exception) {}
+        }
+    }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         // Ensure the shared audio_service engine exists before the activity
         // delegate looks it up by cached id (see getCachedEngineId above).
@@ -2102,6 +2125,7 @@ class MainActivity: FlutterFragmentActivity() {
     override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
         super.configureFlutterEngine(flutterEngine)
         Gobackend.setAppVersion(BuildConfig.VERSION_NAME)
+        sweepStaleCacheFiles()
 
         // Always-enabled back callback to ensure back presses reach Flutter.
         // Nested tab navigators can incorrectly set frameworkHandlesBack(false),