perf(download): reduce progress wakeups and harden retries

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

@@ -374,6 +374,7 @@ class DownloadService : Service() {
     @Volatile private var nativeWorkerCancelRequested = false
     internal var nativeWorkerDownloadNetworkMode = "any"
     internal var nativeWorkerNetworkCallback: ConnectivityManager.NetworkCallback? = null
+    internal var nativeWorkerNetworkFallbackJob: Job? = null
     internal val nativeWorkerWifiNetworks = mutableSetOf<Network>()
     // Bumped every time a new native queue replaces the current one. A worker
     // coroutine that observes a different generation than its own must stop

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

@@ -94,6 +94,17 @@ internal fun DownloadService.configureNativeWorkerNetworkPolicy(settingsJson: St
             "DownloadService",
             "Failed to monitor Wi-Fi for native worker: ${e.message}",
         )
+        // Callback registration can fail when the process/system callback quota is
+        // exhausted. Keep the Wi-Fi-only queue observable instead of leaving it
+        // paused forever with no event capable of resuming it.
+        nativeWorkerNetworkFallbackJob?.cancel()
+        nativeWorkerNetworkFallbackJob = serviceScope.launch {
+            while (NativeWorkerPolicy.requiresWifi(nativeWorkerDownloadNetworkMode)) {
+                delay(5_000)
+                refreshNativeWorkerNetworkPause()
+                if (nativeWorkerJob?.isActive != true) break
+            }
+        }
     }
 }
 
@@ -159,6 +170,8 @@ internal fun DownloadService.refreshNativeWorkerNetworkPause() {
 }
 
 internal fun DownloadService.unregisterNativeWorkerNetworkCallback() {
+    nativeWorkerNetworkFallbackJob?.cancel()
+    nativeWorkerNetworkFallbackJob = null
     val callback = nativeWorkerNetworkCallback
     nativeWorkerNetworkCallback = null
     synchronized(nativeWorkerWifiNetworks) {

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

@@ -329,7 +329,7 @@ internal fun DownloadService.cancelNativeWorkerProgressCoordinator() {
 private fun DownloadService.pollNativeWorkerProgress(generation: Long): Set<String> {
     val sinceSeq = synchronized(nativeWorkerProgressLock) { nativeWorkerProgressSeq }
     val raw = try {
-        Gobackend.getAllDownloadProgressDelta(sinceSeq)
+        Gobackend.waitForAllDownloadProgressDelta(sinceSeq, 5_000L)
     } catch (_: Exception) {
         return emptySet()
     }

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

@@ -66,7 +66,6 @@ class MainActivity: FlutterFragmentActivity() {
         "com.zarz.spotiflac/download_progress_stream"
     private val LIBRARY_SCAN_PROGRESS_STREAM_CHANNEL =
         "com.zarz.spotiflac/library_scan_progress_stream"
-    private val DOWNLOAD_PROGRESS_STREAM_POLLING_INTERVAL_MS = 1200L
     // 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
@@ -482,12 +481,17 @@ class MainActivity: FlutterFragmentActivity() {
             while (isActive && downloadProgressEventSink === sink) {
                 try {
                     val payload = withContext(Dispatchers.IO) {
-                        Gobackend.getAllDownloadProgressDelta(lastDownloadProgressSeq)
+                        Gobackend.waitForAllDownloadProgressDelta(
+                            lastDownloadProgressSeq,
+                            15_000L,
+                        )
                     }
+                    if (!isActive || downloadProgressEventSink !== sink) break
                     if (payload.isNotEmpty() && payload != lastDownloadProgressPayload) {
                         updateDownloadProgressSeq(payload)
                         lastDownloadProgressPayload = payload
                         sink.success(parseJsonPayload(payload))
+                        delay(250L)
                     }
                 } catch (e: Exception) {
                     android.util.Log.w(
@@ -495,7 +499,7 @@ class MainActivity: FlutterFragmentActivity() {
                         "Download progress stream poll failed: ${e.message}",
                     )
                 }
-                delay(DOWNLOAD_PROGRESS_STREAM_POLLING_INTERVAL_MS)
+                if (downloadProgressEventSink !== sink) break
             }
         }
     }
@@ -517,6 +521,7 @@ class MainActivity: FlutterFragmentActivity() {
                 val initialPayload = withContext(Dispatchers.IO) {
                     readLibraryScanProgressJsonForStream()
                 }
+                if (!isActive || libraryScanProgressEventSink !== sink) return@launch
                 lastLibraryScanProgressPayload = initialPayload
                 sink.success(parseJsonPayload(initialPayload))
             } catch (e: Exception) {
@@ -530,6 +535,7 @@ class MainActivity: FlutterFragmentActivity() {
                     val payload = withContext(Dispatchers.IO) {
                         readLibraryScanProgressJsonForStream()
                     }
+                    if (!isActive || libraryScanProgressEventSink !== sink) break
                     if (payload != lastLibraryScanProgressPayload) {
                         lastLibraryScanProgressPayload = payload
                         sink.success(parseJsonPayload(payload))