simplified code across the app and consolidated duplicated helpers

lib/state/app/modules/chat/bloc/chat_bloc.dart

@@ -1,6 +1,5 @@
 import 'dart:async';
 import 'dart:developer';
-import 'dart:math' as math;
 
 import 'package:flutter/widgets.dart';
 
@@ -10,6 +9,7 @@ import '../../../../../api/marianumcloud/talk/chat/long_poll_chat.dart';
 import '../../../../../api/marianumcloud/talk/room/get_room_response.dart';
 import '../../../../../api/marianumcloud/talk/set_read_marker/set_read_marker.dart';
 import '../../../../../api/marianumcloud/talk/set_read_marker/set_read_marker_params.dart';
+import '../../../../../utils/exponential_backoff.dart';
 import '../../../infrastructure/utility_widgets/loadable_hydrated_bloc/loadable_hydrated_bloc.dart';
 import '../../../infrastructure/utility_widgets/loadable_hydrated_bloc/loadable_hydrated_bloc_event.dart';
 import '../../chat_list/bloc/chat_list_bloc.dart';
@@ -26,7 +26,6 @@ class ChatBloc
   // A loop parked in its request survives stop+start for the same token
   // (pause/resume); the generation retires it so only one loop polls.
   int _pollGeneration = 0;
-  int _backoffMs = 0;
   int _lastKnownMessageId = 0;
   bool _appResumed = true;
 
@@ -68,8 +67,7 @@ class ChatBloc
   @override
   Map<String, dynamic>? toStorage(ChatState state) {
     final response = state.chatResponse;
-    if (response == null ||
-        response.data.length <= _kMaxPersistedMessages) {
+    if (response == null || response.data.length <= _kMaxPersistedMessages) {
       return state.toJson();
     }
     // Keep only the newest N; trimming drops older messages, so there is
@@ -129,9 +127,6 @@ class ChatBloc
     add(Emit((s) => s.copyWith(referenceMessageId: messageId)));
   }
 
-  /// No-op when the bloc has already moved on to a different token: when
-  /// popping a stacked chat (B over A), A's didPopNext runs setToken(A)
-  /// before B's dispose fires.
   /// The chat view may still be popping when the sign-out resets this bloc,
   /// so leaveChat would find no token and the long-poll would keep running.
   @override
@@ -141,6 +136,9 @@ class ChatBloc
     return super.reset();
   }
 
+  /// No-op when the bloc has already moved on to a different token: when
+  /// popping a stacked chat (B over A), A's didPopNext runs setToken(A)
+  /// before B's dispose fires.
   void leaveChat(String fromToken) {
     if ((innerState?.currentToken ?? '') != fromToken) return;
     _chatViewActive = false;
@@ -272,7 +270,6 @@ class ChatBloc
     if (_pollingToken == token) return;
     _stopLongPoll();
     _pollingToken = token;
-    _backoffMs = 0;
     _lastKnownMessageId = _maxMessageId(innerState?.chatResponse);
     unawaited(_pollLoop(token, ++_pollGeneration));
   }
@@ -280,11 +277,11 @@ class ChatBloc
   void _stopLongPoll() {
     _pollingToken = null;
     _pollGeneration++;
-    _backoffMs = 0;
   }
 
   Future<void> _pollLoop(String token, int generation) async {
     bool active() => generation == _pollGeneration && !isClosed;
+    var failures = 0;
     while (active()) {
       try {
         final response = await LongPollChat(
@@ -293,7 +290,7 @@ class ChatBloc
         ).run();
 
         if (!active()) return;
-        _backoffMs = 0;
+        failures = 0;
 
         if (response == null) continue;
 
@@ -318,8 +315,13 @@ class ChatBloc
       } on Object catch (e) {
         if (!active()) return;
         log('LongPoll error for $token: $e');
-        _backoffMs = _backoffMs == 0 ? 2000 : math.min(_backoffMs * 2, 30000);
-        await Future.delayed(Duration(milliseconds: _backoffMs));
+        await Future<void>.delayed(
+          exponentialBackoff(
+            ++failures,
+            base: const Duration(seconds: 2),
+            max: const Duration(seconds: 30),
+          ),
+        );
       }
     }
   }
@@ -339,14 +341,7 @@ class ChatBloc
       );
       return;
     }
-    final byId = <int, GetChatResponseObject>{};
-    for (final m in current.data) {
-      byId[m.id] = m;
-    }
-    for (final m in incoming.data) {
-      byId[m.id] = m;
-    }
-    final merged = GetChatResponse(byId.values.toSet())
+    final merged = _mergeById(current, incoming, incomingWins: true)
       ..headers = incoming.headers;
     add(DataGathered((s) => s.copyWith(chatResponse: merged)));
   }
@@ -357,14 +352,7 @@ class ChatBloc
   void _applyOlderResponse(GetChatResponse older) {
     final current = innerState?.chatResponse;
     if (current == null) return;
-    final byId = <int, GetChatResponseObject>{};
-    for (final m in current.data) {
-      byId[m.id] = m;
-    }
-    for (final m in older.data) {
-      byId.putIfAbsent(m.id, () => m);
-    }
-    final merged = GetChatResponse(byId.values.toSet())
+    final merged = _mergeById(current, older, incomingWins: false)
       ..headers = current.headers;
     add(
       DataGathered(
@@ -377,6 +365,22 @@ class ChatBloc
     );
   }
 
+  GetChatResponse _mergeById(
+    GetChatResponse current,
+    GetChatResponse incoming, {
+    required bool incomingWins,
+  }) {
+    final byId = {for (final m in current.data) m.id: m};
+    for (final m in incoming.data) {
+      if (incomingWins) {
+        byId[m.id] = m;
+      } else {
+        byId.putIfAbsent(m.id, () => m);
+      }
+    }
+    return GetChatResponse(byId.values.toSet());
+  }
+
   int _maxMessageId(GetChatResponse? response) {
     if (response == null) return 0;
     var max = 0;
@@ -386,8 +390,7 @@ class ChatBloc
     return max;
   }
 
-  int _minMessageId(GetChatResponse? response) {
-    if (response == null) return 0;
+  int _minMessageId(GetChatResponse response) {
     var min = 0;
     for (final m in response.data) {
       if (m.id <= 0) continue; // skip dummies