implemented chat long-polling and optimistic updates, centralized notification management, optimized avatar caching

lib/routing/app_routes.dart

@@ -6,6 +6,7 @@ import 'package:persistent_bottom_nav_bar_v2/persistent_bottom_nav_bar_v2.dart';
 import '../api/marianumcloud/talk/room/get_room_response.dart';
 import '../main.dart';
 import '../model/account_data.dart';
+import '../notification/notification_tasks.dart';
 import '../share_intent/pending_share.dart';
 import '../share_intent/remote_file_ref.dart';
 import '../state/app/modules/app_modules.dart';
@@ -39,6 +40,11 @@ class AppRoutes {
   /// by `ChatList` once the matching room is loaded.
   static final ValueNotifier<String?> pendingChatToken = ValueNotifier(null);
 
+  /// Root-navigator observer used by [ChatView] to reclaim the global
+  /// [ChatBloc] on `didPopNext` after a stacked chat is popped.
+  static final RouteObserver<PageRoute<dynamic>> chatRouteObserver =
+      RouteObserver<PageRoute<dynamic>>();
+
   static void openFolder(BuildContext context, List<String> path) {
     pushScreen(context, withNavBar: false, screen: Files(path: path));
   }
@@ -177,6 +183,12 @@ class AppRoutes {
     required UserAvatar avatar,
     bool overrideToSingleSubScreen = true,
   }) {
+    // Local mark only. Server-side mark is sent later from
+    // ChatBloc._loadChat with the freshly-fetched maxId — sending one
+    // here too with the chat list's possibly-stale room.lastMessage.id
+    // would race the fresh one and could regress the server cursor.
+    context.read<ChatListBloc>().markRoomAsRead(room.token, room.lastMessage.id);
+    NotificationTasks.clearNotificationsForChat(room.token);
     TalkNavigator.pushSplitView(
       context,
       ChatView(room: room, selfId: selfId, avatar: avatar),