improved performance and battery usage on older devices

lib/main.dart

@@ -167,6 +167,12 @@ Future<void> main() async {
   await Future.wait(initialisationTasks);
   log('app initialisation done!');
 
+  // Independent of the notification setup below, so it runs alongside it.
+  final widgetSyncInit = _startupStep(
+    'widget sync',
+    WidgetSync.ensureInitialized,
+  );
+
   // Local notifications: init the plugin (with tap/action callbacks) and the
   // Android channels, then register the FCM background isolate handler that
   // decrypts and renders Nextcloud pushes while the app is not in foreground.
@@ -186,9 +192,9 @@ Future<void> main() async {
     ),
   );
 
-  // Wire up the home-screen widget bridge before runApp so any widget render
-  // triggered during startup hits initialised native storage.
-  await _startupStep('widget sync', WidgetSync.ensureInitialized);
+  // The home-screen widget bridge must be ready before runApp so any widget
+  // render triggered during startup hits initialised native storage.
+  await widgetSyncInit;
   unawaited(
     WidgetBackgroundTask.initialize().onError(
       (e, _) => log('Workmanager init failed: $e'),
@@ -271,6 +277,10 @@ class Main extends StatefulWidget {
 }
 
 class _MainState extends State<Main> {
+  final List<NavigatorObserver> _navigatorObservers = [
+    AppRoutes.chatRouteObserver,
+    DownloadRouteObserver(),
+  ];
   bool _showPostLoginSplash = false;
   bool _appMounted = true;
   late AccountStatus _lastStatus;
@@ -364,39 +374,45 @@ class _MainState extends State<Main> {
   @override
   Widget build(BuildContext context) => Directionality(
     textDirection: TextDirection.ltr,
-    child: BlocBuilder<SettingsCubit, Settings>(
-      builder: (context, settings) {
-        final devToolsSettings = settings.devToolsSettings;
+    // Selects only what the root uses: Settings is mutated in place and
+    // re-emitted as a fresh instance on every write, so a plain BlocBuilder
+    // would rebuild MaterialApp (and every route) for unrelated settings.
+    child: BlocSelector<SettingsCubit, Settings, _RootSettings>(
+      selector: (settings) => (
+        appTheme: settings.appTheme,
+        mcBaseUrl: settings.devToolsSettings.resolveMarianumConnectBaseUrl(),
+        notificationsEnabled: settings.notificationSettings.enabled,
+        showPerformanceOverlay:
+            settings.devToolsSettings.showPerformanceOverlay,
+        checkerboardOffscreenLayers:
+            settings.devToolsSettings.checkerboardOffscreenLayers,
+        checkerboardRasterCacheImages:
+            settings.devToolsSettings.checkerboardRasterCacheImages,
+      ),
+      builder: (context, root) {
         // Keep the MC dio singleton aligned with the currently selected
         // endpoint (live / beta / custom). Idempotent when the URL is
-        // unchanged so it's safe to call on every rebuild. Mirrored into
-        // WidgetSync so the background isolate refreshes against the same
-        // endpoint.
-        final mcBaseUrl = devToolsSettings.resolveMarianumConnectBaseUrl();
-        MarianumConnectEndpoint.update(mcBaseUrl);
-        unawaited(WidgetSync.setMarianumConnectBaseUrl(mcBaseUrl));
+        // unchanged. Mirrored into WidgetSync so the background isolate
+        // refreshes against the same endpoint.
+        MarianumConnectEndpoint.update(root.mcBaseUrl);
+        unawaited(WidgetSync.setMarianumConnectBaseUrl(root.mcBaseUrl));
         // Mirror the notification toggle into group-scoped storage so the FCM
         // background isolate and the iOS NSE can suppress rendering when off.
         unawaited(
           const PushRegistrationStore().setNotificationsEnabled(
-            settings.notificationSettings.enabled,
+            root.notificationsEnabled,
           ),
         );
         return MaterialApp(
-          showPerformanceOverlay: devToolsSettings.showPerformanceOverlay,
-          checkerboardOffscreenLayers:
-              devToolsSettings.checkerboardOffscreenLayers,
-          checkerboardRasterCacheImages:
-              devToolsSettings.checkerboardRasterCacheImages,
+          showPerformanceOverlay: root.showPerformanceOverlay,
+          checkerboardOffscreenLayers: root.checkerboardOffscreenLayers,
+          checkerboardRasterCacheImages: root.checkerboardRasterCacheImages,
           debugShowCheckedModeBanner: false,
           navigatorKey: AppRoutes.rootNavigatorKey,
           // Used by ChatView.didPopNext to reclaim the global ChatBloc.
           // DownloadRouteObserver tracks full-page navigations so the downloads
           // chip only surfaces once the user leaves the screen they started on.
-          navigatorObservers: [
-            AppRoutes.chatRouteObserver,
-            DownloadRouteObserver(),
-          ],
+          navigatorObservers: _navigatorObservers,
           localizationsDelegates: const [
             ...GlobalMaterialLocalizations.delegates,
             GlobalWidgetsLocalizations.delegate,
@@ -404,7 +420,7 @@ class _MainState extends State<Main> {
           supportedLocales: const [Locale('de'), Locale('en')],
           locale: const Locale('de'),
           title: 'Marianum Fulda',
-          themeMode: settings.appTheme,
+          themeMode: root.appTheme,
           theme: LightAppTheme.theme,
           darkTheme: DarkAppTheme.theme,
           // Brand-colored backdrop behind every route. During the logout
@@ -527,3 +543,12 @@ class _MainState extends State<Main> {
     ),
   );
 }
+
+typedef _RootSettings = ({
+  ThemeMode appTheme,
+  String mcBaseUrl,
+  bool notificationsEnabled,
+  bool showPerformanceOverlay,
+  bool checkerboardOffscreenLayers,
+  bool checkerboardRasterCacheImages,
+});