fixed bug that prevents sending messages if reply was triggered in a different chat

lib/view/pages/talk/widgets/chat_textfield.dart

@@ -11,6 +11,7 @@ import '../../../../api/marianumcloud/talk/send_message/send_message_params.dart
 import '../../../../api/marianumcloud/talk/share_files_to_chat.dart';
 import '../../../../api/marianumcloud/webdav/webdav_api.dart';
 import '../../../../state/app/modules/chat/bloc/chat_bloc.dart';
+import '../../../../state/app/modules/chat/bloc/chat_state.dart';
 import '../../../../state/app/modules/settings/bloc/settings_cubit.dart';
 import '../../../../widget/async_action_button.dart';
 import '../../../../widget/demo_restricted.dart';
@@ -216,11 +217,27 @@ class _ChatTextfieldState extends State<ChatTextfield> {
     _setDraft(newText);
   }
 
+  /// Reply target for the next send, or null when there is none. Requires the
+  /// referenced message to sit in this room's loaded history — the same
+  /// criterion the reply banner renders on, so what the user sees is what gets
+  /// sent. Talk rejects the whole message when the parent id is foreign to the
+  /// room, so a leftover reference would otherwise block the chat entirely.
+  String? _replyTargetFor(ChatState? chatState) {
+    final referenceId = chatState?.referenceMessageId;
+    if (referenceId == null) return null;
+    if (chatState!.currentToken != widget.sendToToken) return null;
+    final messages = chatState.chatResponse?.data;
+    if (messages == null || !messages.any((e) => e.id == referenceId)) {
+      return null;
+    }
+    return referenceId.toString();
+  }
+
   Future<void> _sendMessage(ChatBloc chatBloc) async {
     if (_textBoxController.text.isEmpty) return;
     if (guardDemoAction(context)) return;
     final text = _textBoxController.text;
-    final replyTo = chatBloc.state.data?.referenceMessageId?.toString();
+    final replyTo = _replyTargetFor(chatBloc.state.data);
     final ownToken = widget.sendToToken;
     setState(() => _sendError = null);
     await SendMessage(