diff --git a/it0_app/lib/features/chat/data/datasources/chat_remote_datasource.dart b/it0_app/lib/features/chat/data/datasources/chat_remote_datasource.dart
index 9fa198c..c879aed 100644
--- a/it0_app/lib/features/chat/data/datasources/chat_remote_datasource.dart
+++ b/it0_app/lib/features/chat/data/datasources/chat_remote_datasource.dart
@@ -118,9 +118,21 @@ class ChatRemoteDatasource {
     );
   }
 
-  /// Cancels an active agent task in a session.
-  Future<void> cancelTask(String sessionId) async {
-    await _dio.post('${ApiEndpoints.sessions}/$sessionId/cancel');
+  /// Cancels an active agent task by taskId.
+  Future<void> cancelTask(String taskId) async {
+    await _dio.delete('${ApiEndpoints.tasks}/$taskId');
+  }
+
+  /// Injects a message into an active task, cancelling current work and starting new task.
+  Future<Map<String, dynamic>> injectMessage({
+    required String taskId,
+    required String message,
+  }) async {
+    final response = await _dio.post(
+      '${ApiEndpoints.tasks}/$taskId/inject',
+      data: {'message': message},
+    );
+    return response.data as Map<String, dynamic>;
   }
 
   /// Confirms a standing order draft proposed by the agent.
diff --git a/it0_app/lib/features/chat/data/models/stream_event_model.dart b/it0_app/lib/features/chat/data/models/stream_event_model.dart
index c25e85b..247ff0a 100644
--- a/it0_app/lib/features/chat/data/models/stream_event_model.dart
+++ b/it0_app/lib/features/chat/data/models/stream_event_model.dart
@@ -80,6 +80,14 @@ class StreamEventModel {
           data['orderName'] as String? ?? data['order_name'] as String? ?? '',
         );
 
+      case 'task_info':
+        return TaskInfoEvent(
+          data['taskId'] as String? ?? data['task_id'] as String? ?? '',
+        );
+
+      case 'cancelled':
+        return CancelledEvent();
+
       default:
         // Fall back to text event for unknown types
         return TextEvent(
diff --git a/it0_app/lib/features/chat/data/repositories/chat_repository_impl.dart b/it0_app/lib/features/chat/data/repositories/chat_repository_impl.dart
index aecdf0a..673ad0f 100644
--- a/it0_app/lib/features/chat/data/repositories/chat_repository_impl.dart
+++ b/it0_app/lib/features/chat/data/repositories/chat_repository_impl.dart
@@ -41,8 +41,9 @@ class ChatRepositoryImpl implements ChatRepository {
         sessionId;
     final taskId = response['taskId'] as String? ?? response['task_id'] as String?;
 
-    // Emit the real sessionId so the notifier can capture it
+    // Emit the real sessionId and taskId so the notifier can capture them
     yield SessionInfoEvent(returnedSessionId);
+    if (taskId != null) yield TaskInfoEvent(taskId);
 
     // Connect to the agent WebSocket and subscribe to the session
     final token = await _getAccessToken();
@@ -94,8 +95,9 @@ class ChatRepositoryImpl implements ChatRepository {
         sessionId;
     final taskId = response['taskId'] as String? ?? response['task_id'] as String?;
 
-    // Emit the real sessionId so the notifier can capture it
+    // Emit the real sessionId and taskId so the notifier can capture them
     yield SessionInfoEvent(returnedSessionId);
+    if (taskId != null) yield TaskInfoEvent(taskId);
 
     final voiceToken = await _getAccessToken();
     await _webSocketClient.connect('/ws/agent', token: voiceToken);
@@ -153,8 +155,52 @@ class ChatRepositoryImpl implements ChatRepository {
   }
 
   @override
-  Future<void> cancelTask(String sessionId) async {
-    await _remoteDatasource.cancelTask(sessionId);
+  Future<void> cancelTask(String taskId) async {
+    await _remoteDatasource.cancelTask(taskId);
+  }
+
+  @override
+  Stream<StreamEvent> injectMessage({
+    required String taskId,
+    required String message,
+  }) async* {
+    // Call inject API — this cancels the current task and starts a new one
+    final response = await _remoteDatasource.injectMessage(
+      taskId: taskId,
+      message: message,
+    );
+
+    final newTaskId = response['taskId'] as String? ?? response['task_id'] as String?;
+    if (newTaskId != null) {
+      yield TaskInfoEvent(newTaskId);
+    }
+
+    // The WebSocket is already connected and subscribed to this session.
+    // New events from the injected task will flow through the existing connection.
+    yield* _webSocketClient.messages.transform(
+      StreamTransformer<Map<String, dynamic>, StreamEvent>.fromHandlers(
+        handleData: (msg, sink) {
+          final event = msg['event'] as String? ?? msg['type'] as String? ?? '';
+
+          if (event == 'stream_event' || event == 'message') {
+            final data = msg['data'] as Map<String, dynamic>? ?? msg;
+            final model = StreamEventModel.fromJson(data);
+            final entity = model.toEntity();
+            // Skip cancelled events from the old task during inject
+            if (entity is CancelledEvent) return;
+            sink.add(entity);
+          } else if (event == 'stream_end' || event == 'done' || event == 'complete') {
+            final summary = msg['summary'] as String? ?? '';
+            sink.add(CompletedEvent(summary));
+            sink.close();
+          } else if (event == 'error') {
+            final message = msg['message'] as String? ?? '流式传输错误';
+            sink.add(ErrorEvent(message));
+            sink.close();
+          }
+        },
+      ),
+    );
   }
 
   @override
diff --git a/it0_app/lib/features/chat/domain/entities/chat_message.dart b/it0_app/lib/features/chat/domain/entities/chat_message.dart
index 56e1534..9dd98d3 100644
--- a/it0_app/lib/features/chat/domain/entities/chat_message.dart
+++ b/it0_app/lib/features/chat/domain/entities/chat_message.dart
@@ -1,6 +1,6 @@
 enum MessageRole { user, assistant, system }
 
-enum MessageType { text, toolUse, toolResult, approval, thinking, standingOrderDraft }
+enum MessageType { text, toolUse, toolResult, approval, thinking, standingOrderDraft, interrupted }
 
 enum ToolStatus { executing, completed, error, blocked, awaitingApproval }
 
diff --git a/it0_app/lib/features/chat/domain/entities/stream_event.dart b/it0_app/lib/features/chat/domain/entities/stream_event.dart
index 8d837a7..a744d91 100644
--- a/it0_app/lib/features/chat/domain/entities/stream_event.dart
+++ b/it0_app/lib/features/chat/domain/entities/stream_event.dart
@@ -56,3 +56,14 @@ class SessionInfoEvent extends StreamEvent {
   final String sessionId;
   SessionInfoEvent(this.sessionId);
 }
+
+/// Carries the taskId assigned by the backend for cancel tracking.
+class TaskInfoEvent extends StreamEvent {
+  final String taskId;
+  TaskInfoEvent(this.taskId);
+}
+
+/// Emitted when a task is cancelled (by user or by injection).
+class CancelledEvent extends StreamEvent {
+  CancelledEvent();
+}
diff --git a/it0_app/lib/features/chat/domain/repositories/chat_repository.dart b/it0_app/lib/features/chat/domain/repositories/chat_repository.dart
index 040e31a..e989831 100644
--- a/it0_app/lib/features/chat/domain/repositories/chat_repository.dart
+++ b/it0_app/lib/features/chat/domain/repositories/chat_repository.dart
@@ -24,8 +24,14 @@ abstract class ChatRepository {
   /// Rejects a pending command approval request with an optional reason.
   Future<void> rejectCommand(String taskId, {String? reason});
 
-  /// Cancels an active agent task within a session.
-  Future<void> cancelTask(String sessionId);
+  /// Cancels an active agent task by taskId.
+  Future<void> cancelTask(String taskId);
+
+  /// Injects a message while agent is working, returns a stream of events for the new task.
+  Stream<StreamEvent> injectMessage({
+    required String taskId,
+    required String message,
+  });
 
   /// Confirms a standing order draft proposed by the agent.
   Future<void> confirmStandingOrder(
diff --git a/it0_app/lib/features/chat/domain/usecases/cancel_task.dart b/it0_app/lib/features/chat/domain/usecases/cancel_task.dart
index 287666f..a46abd9 100644
--- a/it0_app/lib/features/chat/domain/usecases/cancel_task.dart
+++ b/it0_app/lib/features/chat/domain/usecases/cancel_task.dart
@@ -5,7 +5,7 @@ class CancelTask {
 
   CancelTask(this._repository);
 
-  Future<void> execute(String sessionId) {
-    return _repository.cancelTask(sessionId);
+  Future<void> execute(String taskId) {
+    return _repository.cancelTask(taskId);
   }
 }
diff --git a/it0_app/lib/features/chat/presentation/pages/chat_page.dart b/it0_app/lib/features/chat/presentation/pages/chat_page.dart
index 384ea5e..ee12e17 100644
--- a/it0_app/lib/features/chat/presentation/pages/chat_page.dart
+++ b/it0_app/lib/features/chat/presentation/pages/chat_page.dart
@@ -34,6 +34,14 @@ class _ChatPageState extends ConsumerState<ChatPage> {
     _scrollToBottom();
   }
 
+  void _inject() {
+    final text = _messageController.text.trim();
+    if (text.isEmpty) return;
+    _messageController.clear();
+    ref.read(chatProvider.notifier).injectMessage(text);
+    _scrollToBottom();
+  }
+
   void _scrollToBottom() {
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (_scrollController.hasClients) {
@@ -160,6 +168,15 @@ class _ChatPageState extends ConsumerState<ChatPage> {
           ),
         );
 
+      case MessageType.interrupted:
+        return TimelineEventNode(
+          status: NodeStatus.warning,
+          label: message.content,
+          isFirst: isFirst,
+          isLast: isLast,
+          icon: Icons.cancel_outlined,
+        );
+
       case MessageType.text:
       default:
         return TimelineEventNode(
@@ -321,8 +338,8 @@ class _ChatPageState extends ConsumerState<ChatPage> {
   }
 
   Widget _buildInputArea(ChatState chatState) {
-    final isDisabled = chatState.isStreaming ||
-        chatState.agentStatus == AgentStatus.awaitingApproval;
+    final isAwaitingApproval = chatState.agentStatus == AgentStatus.awaitingApproval;
+    final isStreaming = chatState.isStreaming && !isAwaitingApproval;
 
     return Container(
       padding: const EdgeInsets.all(8),
@@ -335,29 +352,40 @@ class _ChatPageState extends ConsumerState<ChatPage> {
           Expanded(
             child: TextField(
               controller: _messageController,
-              decoration: const InputDecoration(
-                hintText: '输入指令...',
-                border: OutlineInputBorder(
+              decoration: InputDecoration(
+                hintText: isStreaming ? '追加指令...' : '输入指令...',
+                border: const OutlineInputBorder(
                   borderRadius: BorderRadius.all(Radius.circular(24)),
                 ),
-                contentPadding: EdgeInsets.symmetric(horizontal: 16, vertical: 10),
+                contentPadding: const EdgeInsets.symmetric(horizontal: 16, vertical: 10),
               ),
               textInputAction: TextInputAction.send,
-              onSubmitted: (_) => _send(),
-              enabled: !isDisabled,
+              onSubmitted: (_) => isStreaming ? _inject() : _send(),
+              enabled: !isAwaitingApproval,
             ),
           ),
           const SizedBox(width: 8),
-          if (chatState.isStreaming)
-            IconButton(
-              icon: const Icon(Icons.stop_circle_outlined, color: AppColors.error),
-              tooltip: '停止',
-              onPressed: () => ref.read(chatProvider.notifier).cancelCurrentTask(),
+          if (isStreaming)
+            // During streaming: show both inject-send and stop buttons
+            Row(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                IconButton(
+                  icon: const Icon(Icons.send, color: AppColors.info),
+                  tooltip: '追加指令',
+                  onPressed: _inject,
+                ),
+                IconButton(
+                  icon: const Icon(Icons.stop_circle_outlined, color: AppColors.error),
+                  tooltip: '停止',
+                  onPressed: () => ref.read(chatProvider.notifier).cancelCurrentTask(),
+                ),
+              ],
             )
           else
             IconButton(
               icon: const Icon(Icons.send),
-              onPressed: isDisabled ? null : _send,
+              onPressed: isAwaitingApproval ? null : _send,
             ),
         ],
       ),
diff --git a/it0_app/lib/features/chat/presentation/providers/chat_providers.dart b/it0_app/lib/features/chat/presentation/providers/chat_providers.dart
index ca8a8c0..de5d3d3 100644
--- a/it0_app/lib/features/chat/presentation/providers/chat_providers.dart
+++ b/it0_app/lib/features/chat/presentation/providers/chat_providers.dart
@@ -86,12 +86,14 @@ class ChatState {
   final List<ChatMessage> messages;
   final AgentStatus agentStatus;
   final String? sessionId;
+  final String? taskId;
   final String? error;
 
   const ChatState({
     this.messages = const [],
     this.agentStatus = AgentStatus.idle,
     this.sessionId,
+    this.taskId,
     this.error,
   });
 
@@ -101,12 +103,15 @@ class ChatState {
     List<ChatMessage>? messages,
     AgentStatus? agentStatus,
     String? sessionId,
+    String? taskId,
     String? error,
+    bool clearTaskId = false,
   }) {
     return ChatState(
       messages: messages ?? this.messages,
       agentStatus: agentStatus ?? this.agentStatus,
       sessionId: sessionId ?? this.sessionId,
+      taskId: clearTaskId ? null : (taskId ?? this.taskId),
       error: error,
     );
   }
@@ -275,12 +280,14 @@ class ChatNotifier extends StateNotifier<ChatState> {
         state = state.copyWith(
           messages: finalMessages,
           agentStatus: AgentStatus.idle,
+          clearTaskId: true,
         );
 
       case ErrorEvent(:final message):
         state = state.copyWith(
           agentStatus: AgentStatus.error,
           error: message,
+          clearTaskId: true,
         );
 
       case StandingOrderDraftEvent(:final draft):
@@ -313,6 +320,16 @@ class ChatNotifier extends StateNotifier<ChatState> {
       case SessionInfoEvent(:final sessionId):
         // Capture the real sessionId from the backend for multi-turn reuse
         state = state.copyWith(sessionId: sessionId);
+
+      case TaskInfoEvent(:final taskId):
+        // Capture the taskId for cancel/inject tracking
+        state = state.copyWith(taskId: taskId);
+
+      case CancelledEvent():
+        // Backend confirmed cancellation — if UI hasn't already gone idle, do it now
+        if (state.agentStatus != AgentStatus.idle) {
+          state = state.copyWith(agentStatus: AgentStatus.idle, clearTaskId: true);
+        }
     }
   }
 
@@ -411,14 +428,123 @@ class ChatNotifier extends StateNotifier<ChatState> {
   }
 
   Future<void> cancelCurrentTask() async {
-    if (state.sessionId == null) return;
+    final taskId = state.taskId;
+    if (taskId == null && state.sessionId == null) return;
+
+    // 1. IMMEDIATELY update UI — optimistic cancel
+    _eventSubscription?.cancel();
+    _eventSubscription = null;
+
+    // Mark any executing tools as completed
+    final updatedMessages = state.messages.map((m) {
+      if (m.type == MessageType.toolUse &&
+          m.toolExecution?.status == ToolStatus.executing) {
+        return m.copyWith(
+          toolExecution: m.toolExecution!.copyWith(status: ToolStatus.completed),
+        );
+      }
+      return m;
+    }).toList();
+
+    // Add interrupted marker to timeline
+    final interruptedMsg = ChatMessage(
+      id: '${DateTime.now().microsecondsSinceEpoch}_interrupted',
+      role: MessageRole.assistant,
+      content: '已中断',
+      timestamp: DateTime.now(),
+      type: MessageType.interrupted,
+    );
+
+    state = state.copyWith(
+      agentStatus: AgentStatus.idle,
+      messages: [...updatedMessages, interruptedMsg],
+      clearTaskId: true,
+      error: null,
+    );
+
+    // 2. Fire-and-forget backend cancel
+    if (taskId != null) {
+      try {
+        final useCase = _ref.read(cancelTaskUseCaseProvider);
+        await useCase.execute(taskId);
+      } catch (_) {
+        // Ignore — UI is already updated
+      }
+    }
+  }
+
+  /// Injects a message while the agent is actively working.
+  /// Cancels the current task and starts a new one with the injected message.
+  Future<void> injectMessage(String message) async {
+    if (message.trim().isEmpty) return;
+    final taskId = state.taskId;
+    if (taskId == null) {
+      // Fallback: if no active task, treat as normal send
+      return sendMessage(message);
+    }
+
+    // 1. Cancel current event subscription
+    _eventSubscription?.cancel();
+    _eventSubscription = null;
+
+    // 2. Mark executing tools as completed
+    final updatedMessages = state.messages.map((m) {
+      if (m.type == MessageType.toolUse &&
+          m.toolExecution?.status == ToolStatus.executing) {
+        return m.copyWith(
+          toolExecution: m.toolExecution!.copyWith(status: ToolStatus.completed),
+        );
+      }
+      return m;
+    }).toList();
+
+    // 3. Add interrupted marker + user message to timeline
+    final interruptedMsg = ChatMessage(
+      id: '${DateTime.now().microsecondsSinceEpoch}_interrupted',
+      role: MessageRole.assistant,
+      content: '已中断 (用户追加指令)',
+      timestamp: DateTime.now(),
+      type: MessageType.interrupted,
+    );
+    final userMsg = ChatMessage(
+      id: DateTime.now().microsecondsSinceEpoch.toString(),
+      role: MessageRole.user,
+      content: message,
+      timestamp: DateTime.now(),
+      type: MessageType.text,
+    );
+
+    state = state.copyWith(
+      messages: [...updatedMessages, interruptedMsg, userMsg],
+      agentStatus: AgentStatus.thinking,
+      clearTaskId: true,
+      error: null,
+    );
+
+    // 4. Call the inject API and listen to new event stream
     try {
-      final useCase = _ref.read(cancelTaskUseCaseProvider);
-      await useCase.execute(state.sessionId!);
-      _eventSubscription?.cancel();
-      state = state.copyWith(agentStatus: AgentStatus.idle);
+      final repo = _ref.read(chatRepositoryProvider);
+      final stream = repo.injectMessage(taskId: taskId, message: message);
+
+      _eventSubscription = stream.listen(
+        (event) => _handleStreamEvent(event),
+        onError: (error) {
+          state = state.copyWith(
+            agentStatus: AgentStatus.error,
+            error: ErrorHandler.friendlyMessage(error),
+          );
+        },
+        onDone: () {
+          if (state.agentStatus != AgentStatus.error) {
+            state = state.copyWith(agentStatus: AgentStatus.idle);
+          }
+        },
+      );
     } catch (e) {
-      state = state.copyWith(error: '取消失败: $e');
+      state = state.copyWith(
+        agentStatus: AgentStatus.error,
+        error: ErrorHandler.friendlyMessage(e),
+      );
     }
   }
 
diff --git a/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts b/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts
index 5df48c6..0bbc294 100644
--- a/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts
+++ b/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts
@@ -37,4 +37,6 @@ export type EngineStreamEvent =
   | { type: 'tool_result'; toolName: string; output: string; isError: boolean }
   | { type: 'approval_required'; command: string; riskLevel: number; taskId: string }
   | { type: 'completed'; summary: string; tokensUsed?: number }
-  | { type: 'error'; message: string; code: string };
+  | { type: 'error'; message: string; code: string }
+  | { type: 'cancelled'; message: string; code: string }
+  | { type: 'task_info'; taskId: string };