feat: implement Fork thread branching, Archive, Branch, Resend, and English menu labels

apps/mobile_chat_app/lib/features/chat/chat_history_api_service.dart

@@ -65,6 +65,18 @@ class ChatAcceptedTask {
   final String acceptedAt;
 }
 
+class ChatForkResult {
+  const ChatForkResult({
+    required this.threadId,
+    required this.channelId,
+    required this.forkedSessionId,
+  });
+
+  final String threadId;
+  final String channelId;
+  final String forkedSessionId;
+}
+
 class ChatChannelNameSetting {
   const ChatChannelNameSetting({
     required this.channelId,
@@ -134,6 +146,7 @@ class ChatHistoryApiService {
   Uri get _scopesUri => Uri.parse('$_base/api/chat/scopes');
   Uri get _scopeSettingsUri => Uri.parse('$_base/api/chat/scope-settings');
   Uri get _channelNamesUri => Uri.parse('$_base/api/chat/channel-names');
+  Uri get _forkUri => Uri.parse('$_base/api/chat/fork');
 
   ChatTaskState? _parseTaskState(Object? value) {
     if (value is! String || value.isEmpty) return null;
@@ -521,6 +534,32 @@ class ChatHistoryApiService {
         .toList(growable: false);
   }
 
+  Future<ChatForkResult> forkThread({
+    required String parentSessionId,
+    required String forkMessageId,
+    required String newThreadId,
+  }) async {
+    final response = await _apiClient.post(
+      _forkUri,
+      headers: {'Content-Type': 'application/json'},
+      body: jsonEncode({
+        'parentSessionId': parentSessionId,
+        'forkMessageId': forkMessageId,
+        'newThreadId': newThreadId,
+      }),
+    );
+    if (response.statusCode != 200) {
+      throw Exception('Failed to fork thread (${response.statusCode})');
+    }
+    final raw = jsonDecode(response.body);
+    if (raw is! Map) throw Exception('Invalid fork response');
+    return ChatForkResult(
+      threadId: raw['threadId'] as String,
+      channelId: raw['channelId'] as String,
+      forkedSessionId: raw['forkedSessionId'] as String,
+    );
+  }
+
   Future<int> upsertMessages({
     required List<ChatMessage> messages,
   }) async {

apps/mobile_chat_app/lib/features/chat/chat_screen.dart

@@ -46,6 +46,7 @@ class ChatScreen extends StatefulWidget {
 
 class _ChatScreenState extends State<ChatScreen> {
   final List<ChatMessage> _messages = [];
+  final Set<String> _archivedMessageIds = {};
   bool _isSending = false;
   bool _isStreaming = false;
   bool _loadingAgents = true;
@@ -847,6 +848,7 @@ class _ChatScreenState extends State<ChatScreen> {
           _activeChannelId = id;
           _activeSubSection = 'main';
           _messages.clear();
+          _archivedMessageIds.clear();
           _latestCheckpointCursor = null;
           _lastSyncedSeq = 0;
         });
@@ -1055,6 +1057,7 @@ class _ChatScreenState extends State<ChatScreen> {
       _activeChannelId = resolvedChannelId;
       _activeSubSection = restoredSubSection;
       _messages.clear();
+      _archivedMessageIds.clear();
       _latestCheckpointCursor = null;
       _lastSyncedSeq = 0;
     });
@@ -1133,6 +1136,7 @@ class _ChatScreenState extends State<ChatScreen> {
       if (!mounted || _isScopeStale()) return;
       setState(() {
         _messages.clear();
+        _archivedMessageIds.clear();
         _highlights = const {};
         _textHighlights = const [];
         _latestCheckpointCursor = null;
@@ -1228,6 +1232,89 @@ class _ChatScreenState extends State<ChatScreen> {
     }
   }
 
+  void _handleArchiveRound(ChatMessage message) {
+    final messageId = message.messageId;
+    if (messageId == null) return;
+    // Find the user message that immediately precedes this assistant message.
+    String? precedingUserMessageId;
+    bool foundTarget = false;
+    for (int i = _messages.length - 1; i >= 0; i--) {
+      final msg = _messages[i];
+      if (!foundTarget) {
+        if (msg.messageId == messageId) foundTarget = true;
+      } else if (msg.role == 'user') {
+        precedingUserMessageId = msg.messageId;
+        break;
+      }
+    }
+    setState(() {
+      _archivedMessageIds.add(messageId);
+      if (precedingUserMessageId != null) {
+        _archivedMessageIds.add(precedingUserMessageId);
+      }
+    });
+  }
+
+  void _handleArchiveReply(ChatMessage message) {
+    final messageId = message.messageId;
+    if (messageId == null) return;
+    setState(() {
+      _archivedMessageIds.add(messageId);
+    });
+  }
+
+  Future<void> _handleFork(ChatMessage message) async {
+    final messageId = message.messageId;
+    if (messageId == null) return;
+    final parentSessionId = _sessionIdForScope;
+    final newThreadId = _newId('fork');
+    try {
+      await _chatHistoryApiService.forkThread(
+        parentSessionId: parentSessionId,
+        forkMessageId: messageId,
+        newThreadId: newThreadId,
+      );
+    } catch (e) {
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text('Fork failed: $e')),
+      );
+      return;
+    }
+    if (!mounted) return;
+    final section = ChatSubSection(
+      id: newThreadId,
+      parentChannelId: _activeChannelId,
+      name: _timestampName(prefix: 'fork'),
+      createdAt: DateTime.now(),
+    );
+    setState(() {
+      final items = _channelSubSections.putIfAbsent(
+        _activeChannelId,
+        () => <ChatSubSection>[],
+      );
+      items.add(section);
+      _activeSubSection = newThreadId;
+      _lastActiveSubSectionByChannel[_activeChannelId] = newThreadId;
+      _messages.clear();
+      _archivedMessageIds.clear();
+      _latestCheckpointCursor = null;
+      _lastSyncedSeq = 0;
+    });
+    _configureActiveScopeSync();
+  }
+
+  Future<void> _handleBranch(ChatMessage message) async {
+    // Branch forks from the user message itself — the new thread inherits
+    // context up to and including this user message from the parent.
+    await _handleFork(message);
+  }
+
+  void _handleResend(ChatMessage message) {
+    if (message.content.trim().isEmpty) return;
+    _sendMessage(message.content);
+  }
+
   String _subSectionKey(String channelId, String sectionId) =>
       '$channelId::$sectionId';
 
@@ -2221,6 +2308,7 @@ class _ChatScreenState extends State<ChatScreen> {
       _activeSubSection = id;
       _lastActiveSubSectionByChannel[_activeChannelId] = id;
       _messages.clear();
+      _archivedMessageIds.clear();
       _latestCheckpointCursor = null;
       _lastSyncedSeq = 0;
     });
@@ -2298,6 +2386,7 @@ class _ChatScreenState extends State<ChatScreen> {
       _lastActiveSubSectionByChannel[channelId] = 'main';
       _activeSubSection = 'main';
       _messages.clear();
+      _archivedMessageIds.clear();
       _latestCheckpointCursor = null;
       _lastSyncedSeq = 0;
     });
@@ -2324,6 +2413,7 @@ class _ChatScreenState extends State<ChatScreen> {
       _activeSubSection = subSectionId;
       _lastActiveSubSectionByChannel[_activeChannelId] = subSectionId;
       _messages.clear();
+      _archivedMessageIds.clear();
       _latestCheckpointCursor = null;
       _lastSyncedSeq = 0;
     });
@@ -2950,10 +3040,21 @@ class _ChatScreenState extends State<ChatScreen> {
       children: [
         Expanded(
           child: MessageList(
-            messages: _messages,
+            messages: _archivedMessageIds.isEmpty
+                ? _messages
+                : _messages
+                    .where((m) =>
+                        m.messageId == null ||
+                        !_archivedMessageIds.contains(m.messageId))
+                    .toList(),
             highlights: _highlights,
             onHighlight: _handleHighlight,
             onDeleteHighlight: _handleDeleteHighlight,
+            onArchiveRound: _handleArchiveRound,
+            onArchiveReply: _handleArchiveReply,
+            onFork: _handleFork,
+            onBranch: _handleBranch,
+            onResend: _handleResend,
           ),
         ),
         Builder(

apps/mobile_chat_app/lib/features/chat/widgets/message_list.dart

@@ -46,7 +46,9 @@ class MessageList extends StatefulWidget {
     this.onDeleteHighlight,
     this.onArchiveRound,
     this.onArchiveReply,
-    this.onMoveToThread,
+    this.onFork,
+    this.onBranch,
+    this.onResend,
   });
 
   final List<ChatMessage> messages;
@@ -66,14 +68,20 @@ class MessageList extends StatefulWidget {
   /// Called when the user taps Remove highlight in the floating highlight menu.
   final void Function(String highlightId)? onDeleteHighlight;
 
-  /// Called when the user selects "归档此轮" from the assistant message menu.
+  /// Called when the user selects "Archive Round" from the assistant message menu.
   final void Function(ChatMessage message)? onArchiveRound;
 
-  /// Called when the user selects "归档此回复" from the assistant message menu.
+  /// Called when the user selects "Archive Reply" from the assistant message menu.
   final void Function(ChatMessage message)? onArchiveReply;
 
-  /// Called when the user selects "移入Thread" from the assistant message menu.
-  final void Function(ChatMessage message)? onMoveToThread;
+  /// Called when the user selects "Fork" from the assistant message menu.
+  final void Function(ChatMessage message)? onFork;
+
+  /// Called when the user selects "Branch" from the user message context menu.
+  final void Function(ChatMessage message)? onBranch;
+
+  /// Called when the user selects "Resend" from the user message context menu.
+  final void Function(ChatMessage message)? onResend;
 
   @override
   State<MessageList> createState() => _MessageListState();
@@ -439,10 +447,10 @@ class _MessageListState extends State<MessageList> {
         ).showSnackBar(const SnackBar(content: Text('Copied')));
         break;
       case 'branch':
+        widget.onBranch?.call(message);
+        break;
       case 'resend':
-        ScaffoldMessenger.of(
-          context,
-        ).showSnackBar(const SnackBar(content: Text('Coming soon')));
+        widget.onResend?.call(message);
         break;
     }
   }
@@ -454,8 +462,8 @@ class _MessageListState extends State<MessageList> {
   }) async {
     final hasArchiveRound = widget.onArchiveRound != null;
     final hasArchiveReply = widget.onArchiveReply != null;
-    final hasMoveToThread = widget.onMoveToThread != null;
-    if (!hasArchiveRound && !hasArchiveReply && !hasMoveToThread) return;
+    final hasFork = widget.onFork != null;
+    if (!hasArchiveRound && !hasArchiveReply && !hasFork) return;
     final overlay = Overlay.of(context).context.findRenderObject() as RenderBox;
     final result = await showGeneralDialog<String>(
       context: context,
@@ -468,7 +476,7 @@ class _MessageListState extends State<MessageList> {
         screenSize: overlay.size,
         showArchiveRound: hasArchiveRound,
         showArchiveReply: hasArchiveReply,
-        showMoveToThread: hasMoveToThread,
+        showFork: hasFork,
       ),
     );
     if (!context.mounted || result == null) return;
@@ -479,8 +487,8 @@ class _MessageListState extends State<MessageList> {
       case 'archive_reply':
         widget.onArchiveReply?.call(message);
         break;
-      case 'move_to_thread':
-        widget.onMoveToThread?.call(message);
+      case 'fork':
+        widget.onFork?.call(message);
         break;
     }
   }
@@ -2670,8 +2678,8 @@ class _UserMessageContextMenu extends StatelessWidget {
               crossAxisAlignment: CrossAxisAlignment.stretch,
               children: [
                 _MenuItem(label: 'Copy', value: 'copy'),
-                _MenuItem(label: 'Branch (coming soon)', value: 'branch'),
-                _MenuItem(label: 'Resend (coming soon)', value: 'resend'),
+                _MenuItem(label: 'Branch', value: 'branch'),
+                _MenuItem(label: 'Resend', value: 'resend'),
                 Container(
                   padding: const EdgeInsets.symmetric(
                     horizontal: 16,
@@ -2739,14 +2747,14 @@ class _AssistantMessageActionMenu extends StatelessWidget {
     required this.screenSize,
     required this.showArchiveRound,
     required this.showArchiveReply,
-    required this.showMoveToThread,
+    required this.showFork,
   });
 
   final Offset position;
   final Size screenSize;
   final bool showArchiveRound;
   final bool showArchiveReply;
-  final bool showMoveToThread;
+  final bool showFork;
 
   static const double _menuWidth = 200.0;
   static const double _itemHeight = 48.0;
@@ -2755,9 +2763,9 @@ class _AssistantMessageActionMenu extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final items = [
-      if (showArchiveRound) const _MenuItem(label: '归档此轮', value: 'archive_round'),
-      if (showArchiveReply) const _MenuItem(label: '归档此回复', value: 'archive_reply'),
-      if (showMoveToThread) const _MenuItem(label: '移入Thread', value: 'move_to_thread'),
+      if (showArchiveRound) const _MenuItem(label: 'Archive Round', value: 'archive_round'),
+      if (showArchiveReply) const _MenuItem(label: 'Archive Reply', value: 'archive_reply'),
+      if (showFork) const _MenuItem(label: 'Fork', value: 'fork'),
     ];
     final menuHeight = _itemHeight * items.length;
 

apps/mobile_chat_app/test/message_list_test.dart

@@ -40,7 +40,7 @@ Widget _build(
   void Function(String)? onDeleteHighlight,
   void Function(ChatMessage)? onArchiveRound,
   void Function(ChatMessage)? onArchiveReply,
-  void Function(ChatMessage)? onMoveToThread,
+  void Function(ChatMessage)? onFork,
 }) =>
     MaterialApp(
       theme: theme,
@@ -54,7 +54,7 @@ Widget _build(
             onDeleteHighlight: onDeleteHighlight,
             onArchiveRound: onArchiveRound,
             onArchiveReply: onArchiveReply,
-            onMoveToThread: onMoveToThread,
+            onFork: onFork,
           ),
         ),
       ),
@@ -1637,22 +1637,22 @@ void main() {
       expect(received?.messageId, 'a-action');
     });
 
-    testWidgets('tapping move_to_thread calls onMoveToThread with message',
+    testWidgets('tapping fork calls onFork with message',
         (tester) async {
       ChatMessage? received;
       await tester.pumpWidget(
         _build(
           [_assistantMsg()],
-          onMoveToThread: (m) => received = m,
+          onFork: (m) => received = m,
         ),
       );
       await tester.pumpAndSettle();
 
       await tester.tap(find.byIcon(Icons.more_horiz));
       await tester.pumpAndSettle();
 
-      expect(find.text('移入Thread'), findsOneWidget);
-      await tester.tap(find.text('移入Thread'));
+      expect(find.text('Fork'), findsOneWidget);
+      await tester.tap(find.text('Fork'));
       await tester.pumpAndSettle();
 
       expect(received?.messageId, 'a-action');