fix(downloads/extensions): iOS background task, serialize extension mutations, safer batch convert sheet

- iOS: begin/end UIBackgroundTask while a download queue is active so in-flight downloads survive backgrounding for the limited window iOS allows

- extensions: serialize install/upgrade/remove in the Go manager (mutationMu) and in the Dart store provider to stop concurrent goja VM teardown/reload from hard-crashing the app

- main: add runZonedGuarded + FlutterError/PlatformDispatcher onError so uncaught Dart errors are logged, not fatal

- batch convert sheet: precompute localized title/label before showModalBottomSheet to avoid Localizations lookup via a deactivated context

lib/main.dart

@@ -15,20 +15,45 @@ import 'package:spotiflac_android/services/notification_service.dart';
 import 'package:spotiflac_android/services/share_intent_service.dart';
 import 'package:spotiflac_android/services/cover_cache_manager.dart';
 import 'package:spotiflac_android/utils/local_library_scan_prefs.dart';
+import 'package:spotiflac_android/utils/logger.dart';
 
-void main() async {
-  WidgetsFlutterBinding.ensureInitialized();
-  final runtimeProfile = await _resolveRuntimeProfile();
-  _configureImageCache(runtimeProfile);
+final _log = AppLogger('Main');
 
-  runApp(
-    ProviderScope(
-      child: _EagerInitialization(
-        child: SpotiFLACApp(
-          disableOverscrollEffects: runtimeProfile.disableOverscrollEffects,
+void main() {
+  // Catch uncaught errors so a failure in a provider/async path (e.g. a
+  // misbehaving extension request) is logged instead of taking the whole app
+  // down. Native (Go) fatal crashes can't be caught here, but Dart-side ones
+  // can.
+  runZonedGuarded(
+    () async {
+      WidgetsFlutterBinding.ensureInitialized();
+
+      final previousOnError = FlutterError.onError;
+      FlutterError.onError = (details) {
+        previousOnError?.call(details);
+        _log.e('Uncaught Flutter error: ${details.exceptionAsString()}');
+      };
+      WidgetsBinding.instance.platformDispatcher.onError = (error, stack) {
+        _log.e('Uncaught platform error: $error');
+        return true;
+      };
+
+      final runtimeProfile = await _resolveRuntimeProfile();
+      _configureImageCache(runtimeProfile);
+
+      runApp(
+        ProviderScope(
+          child: _EagerInitialization(
+            child: SpotiFLACApp(
+              disableOverscrollEffects: runtimeProfile.disableOverscrollEffects,
+            ),
+          ),
         ),
-      ),
-    ),
+      );
+    },
+    (error, stack) {
+      _log.e('Uncaught zone error: $error');
+    },
   );
 }
 

lib/providers/download_queue_provider.dart

@@ -6676,6 +6676,13 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
       }
     }
 
+    // iOS has no foreground service; request a background execution window so
+    // an in-flight download can keep running for a short time after the app is
+    // backgrounded instead of being suspended immediately.
+    if (Platform.isIOS && _totalQueuedAtStart > 0) {
+      await PlatformBridge.beginBackgroundDownloadTask();
+    }
+
     if (!isSafMode && state.outputDir.isEmpty) {
       _log.d('Output dir empty, initializing...');
       await _initOutputDir();
@@ -6794,6 +6801,10 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
       }
     }
 
+    if (Platform.isIOS) {
+      await PlatformBridge.endBackgroundDownloadTask();
+    }
+
     if (_downloadCount > 0) {
       _log.d('Final connection cleanup...');
       try {

lib/providers/store_provider.dart

@@ -1,4 +1,5 @@
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'dart:async';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:spotiflac_android/constants/app_info.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
@@ -205,6 +206,24 @@ class StoreState {
 }
 
 class StoreNotifier extends Notifier<StoreState> {
+  /// Serializes extension install/upgrade operations. Running two of these at
+  /// once (e.g. updating two extensions simultaneously) races the native
+  /// extension manager's goja VM teardown/reload and can hard-crash the app, so
+  /// they must run strictly one at a time.
+  Future<void> _mutationChain = Future<void>.value();
+
+  Future<T> _runSerialized<T>(Future<T> Function() action) {
+    final completer = Completer<T>();
+    _mutationChain = _mutationChain.then((_) async {
+      try {
+        completer.complete(await action());
+      } catch (e, st) {
+        completer.completeError(e, st);
+      }
+    });
+    return completer.future;
+  }
+
   @override
   StoreState build() {
     return const StoreState();
@@ -330,6 +349,16 @@ class StoreNotifier extends Notifier<StoreState> {
     String extensionId,
     String tempDir,
     String extensionsDir,
+  ) {
+    return _runSerialized(
+      () => _installExtensionInternal(extensionId, tempDir, extensionsDir),
+    );
+  }
+
+  Future<bool> _installExtensionInternal(
+    String extensionId,
+    String tempDir,
+    String extensionsDir,
   ) async {
     state = state.copyWith(
       isDownloading: true,
@@ -366,7 +395,16 @@ class StoreNotifier extends Notifier<StoreState> {
     }
   }
 
-  Future<bool> updateExtension(String extensionId, String tempDir) async {
+  Future<bool> updateExtension(String extensionId, String tempDir) {
+    return _runSerialized(
+      () => _updateExtensionInternal(extensionId, tempDir),
+    );
+  }
+
+  Future<bool> _updateExtensionInternal(
+    String extensionId,
+    String tempDir,
+  ) async {
     state = state.copyWith(
       isDownloading: true,
       downloadingId: extensionId,

lib/screens/downloaded_album_screen.dart

@@ -968,6 +968,11 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
 
     if (formats.isEmpty) return;
 
+    final sheetTitle = context.l10n.selectionBatchConvertConfirmTitle;
+    final sheetConfirmLabel = context.l10n.selectionConvertCount(
+      _selectedIds.length,
+    );
+
     showModalBottomSheet<void>(
       context: context,
       useRootNavigator: true,
@@ -976,8 +981,8 @@ class _DownloadedAlbumScreenState extends ConsumerState<DownloadedAlbumScreen> {
       ),
       builder: (sheetContext) => BatchConvertSheet(
         formats: formats,
-        title: context.l10n.selectionBatchConvertConfirmTitle,
-        confirmLabel: context.l10n.selectionConvertCount(_selectedIds.length),
+        title: sheetTitle,
+        confirmLabel: sheetConfirmLabel,
         onConvert: (format, bitrate) {
           Navigator.pop(sheetContext);
           _performBatchConversion(

lib/screens/local_album_screen.dart

@@ -1216,6 +1216,11 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
 
     if (formats.isEmpty) return;
 
+    final sheetTitle = context.l10n.selectionBatchConvertConfirmTitle;
+    final sheetConfirmLabel = context.l10n.selectionConvertCount(
+      _selectedIds.length,
+    );
+
     showModalBottomSheet<void>(
       context: context,
       useRootNavigator: true,
@@ -1224,8 +1229,8 @@ class _LocalAlbumScreenState extends ConsumerState<LocalAlbumScreen> {
       ),
       builder: (sheetContext) => BatchConvertSheet(
         formats: formats,
-        title: context.l10n.selectionBatchConvertConfirmTitle,
-        confirmLabel: context.l10n.selectionConvertCount(_selectedIds.length),
+        title: sheetTitle,
+        confirmLabel: sheetConfirmLabel,
         onConvert: (format, bitrate) {
           Navigator.pop(sheetContext);
           _performBatchConversion(

lib/screens/queue_tab.dart

@@ -4849,6 +4849,14 @@ class _QueueTabState extends ConsumerState<QueueTab> {
 
     var didStartConversion = false;
 
+    // Resolve localized strings up front: the builder closure must not look up
+    // Localizations via the outer (State) context, which may be deactivated by
+    // the time the root-navigator sheet rebuilds.
+    final sheetTitle = context.l10n.selectionBatchConvertConfirmTitle;
+    final sheetConfirmLabel = context.l10n.selectionConvertCount(
+      _selectedIds.length,
+    );
+
     _suppressSelectionOverlay = true;
     _hideSelectionOverlay();
     _hidePlaylistSelectionOverlay();
@@ -4861,8 +4869,8 @@ class _QueueTabState extends ConsumerState<QueueTab> {
       ),
       builder: (sheetContext) => BatchConvertSheet(
         formats: formats,
-        title: context.l10n.selectionBatchConvertConfirmTitle,
-        confirmLabel: context.l10n.selectionConvertCount(_selectedIds.length),
+        title: sheetTitle,
+        confirmLabel: sheetConfirmLabel,
         onConvert: (format, bitrate) {
           didStartConversion = true;
           Navigator.pop(sheetContext);

lib/services/platform_bridge.dart

@@ -865,6 +865,26 @@ class PlatformBridge {
     return result as bool;
   }
 
+  /// iOS only: mark that a download queue is active so the app keeps in-flight
+  /// downloads running for a short window whenever it is backgrounded. iOS
+  /// grants a limited budget (roughly 30s on modern versions) per background
+  /// entry; there is no foreground-service equivalent, so this is best-effort.
+  static Future<void> beginBackgroundDownloadTask() async {
+    if (!Platform.isIOS) return;
+    try {
+      await _channel.invokeMethod('beginBackgroundDownloadTask');
+    } catch (_) {}
+  }
+
+  /// iOS only: mark that the download queue is no longer active (queue finished
+  /// or paused), stopping background-time extension.
+  static Future<void> endBackgroundDownloadTask() async {
+    if (!Platform.isIOS) return;
+    try {
+      await _channel.invokeMethod('endBackgroundDownloadTask');
+    } catch (_) {}
+  }
+
   static Future<void> startNativeDownloadWorker({
     required List<Map<String, dynamic>> requests,
     Map<String, dynamic> settings = const {},