feat: 添加 :new 系统命令创建新会话

- Core: 新增 :new/:n 命令返回 new_session action
- Server: 处理 new_session action 创建新会话
- UI: useChat 添加 onSessionSwitch 回调
- Web/Desktop: ChatPage 和 App 实现会话切换逻辑

packages/ui/src/hooks/useChat.ts

@@ -33,6 +33,8 @@ interface UseChatOptions {
   onSessionUpdated?: (sessionId: string, name: string) => void;
   /** 配置错误回调（如 API Key 未配置） */
   onConfigError?: (error: ConfigErrorPayload) => void;
+  /** 切换会话回调（如 :new 命令创建新会话） */
+  onSessionSwitch?: (newSessionId: string) => void;
 }
 
 interface ChatState {
@@ -52,7 +54,7 @@ interface ChatState {
   currentSubagent: SubagentState | null;
 }
 
-export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdated, onConfigError }: UseChatOptions) {
+export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdated, onConfigError, onSessionSwitch }: UseChatOptions) {
   const [state, setState] = useState<ChatState>({
     messages: [],
     isConnected: false,
@@ -77,10 +79,12 @@ export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdate
   const onSessionNotFoundRef = useRef(onSessionNotFound);
   const onSessionUpdatedRef = useRef(onSessionUpdated);
   const onConfigErrorRef = useRef(onConfigError);
+  const onSessionSwitchRef = useRef(onSessionSwitch);
   onErrorRef.current = onError;
   onSessionNotFoundRef.current = onSessionNotFound;
   onSessionUpdatedRef.current = onSessionUpdated;
   onConfigErrorRef.current = onConfigError;
+  onSessionSwitchRef.current = onSessionSwitch;
 
   // 加载历史消息
   const loadMessages = useCallback(async () => {
@@ -572,7 +576,7 @@ export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdate
               success: boolean;
               message?: string;
               error?: string;
-              action?: { type: string };
+              action?: { type: string; sessionId?: string };
             };
 
             // 处理清空消息操作
@@ -585,6 +589,11 @@ export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdate
               }));
             }
 
+            // 处理新建会话操作
+            if (payload.success && payload.action?.type === 'new_session' && payload.action.sessionId) {
+              onSessionSwitchRef.current?.(payload.action.sessionId);
+            }
+
             // 如果有错误，通过 onError 回调通知
             if (!payload.success && payload.error) {
               onErrorRef.current?.(new Error(payload.error));