fix(workspace): 恢复先删后建并修复新会话初始化时序

- 新会话初始化改为 delete -> create

- 通过初始化就绪门控，确保 history 在创建完成后再加载

- 发送消息前等待初始化完成，避免与初始化并发

frontend/src/app/workspace/chats/[thread_id]/page.tsx

@@ -81,16 +81,23 @@ export default function ChatPage() {
     () => isNewThread && !safeThreadId,
     [isNewThread, safeThreadId],
   );
+  const [isThreadInitReady, setIsThreadInitReady] = useState(false);
 
   const streamThreadId = useMemo(() => {
-    if (isNewThread && createNewSession) {
+    if (!safeThreadId) {
+      return undefined;
+    }
+    // In /new flow, defer history loading until thread init is finished:
+    // delete -> create -> history.
+    if (isNewThread && !isThreadInitReady) {
       return undefined;
     }
     return safeThreadId;
-  }, [createNewSession, isNewThread, safeThreadId]);
+  }, [isNewThread, isThreadInitReady, safeThreadId]);
   const apiClient = useMemo(() => getAPIClient(isMock), [isMock]);
   const warnedMissingThreadIdRef = useRef(false);
   const initializedThreadRef = useRef<string | null>(null);
+  const threadInitPromiseRef = useRef<Promise<void> | null>(null);
 
   const { showNotification } = useNotification();
   const currentSlogan = motivationSlogans[
@@ -130,6 +137,7 @@ export default function ChatPage() {
   useEffect(() => {
     if (!isNewThread) {
       warnedMissingThreadIdRef.current = false;
+      setIsThreadInitReady(true);
       return;
     }
     if (!safeThreadId) {
@@ -137,29 +145,38 @@ export default function ChatPage() {
         warnedMissingThreadIdRef.current = true;
         toast.error(t.chatPage.missingThreadIdForCreate);
       }
+      setIsThreadInitReady(false);
       return;
     }
     warnedMissingThreadIdRef.current = false;
     if (initializedThreadRef.current === safeThreadId) return;
     initializedThreadRef.current = safeThreadId;
-    void apiClient.threads
-      // TODO: 先注释先删除再创建的逻辑
-      // .delete(safeThreadId)
-      // .catch(() => undefined)
-      // .then(() =>
-      //   apiClient.threads.create({
-      //     threadId: safeThreadId,
-      //     ifExists: "raise",
-      //   }),
-      // )
-      .create({
+    setIsThreadInitReady(false);
+
+    const initPromise = apiClient.threads
+      .delete(safeThreadId)
+      .catch(() => undefined)
+      .then(() =>
+        apiClient.threads.create({
           threadId: safeThreadId,
           ifExists: "do_nothing",
+        }),
+      )
+      .then(() => {
+        setIsThreadInitReady(true);
       })
       .catch(() => {
         initializedThreadRef.current = null;
+        setIsThreadInitReady(false);
         toast.error(t.chatPage.createSessionFailed);
       });
+
+    threadInitPromiseRef.current = initPromise;
+    void initPromise.finally(() => {
+      if (threadInitPromiseRef.current === initPromise) {
+        threadInitPromiseRef.current = null;
+      }
+    });
   }, [
     apiClient,
     isNewThread,
@@ -291,7 +308,7 @@ export default function ChatPage() {
   const [showExitDialog, setShowExitDialog] = useState(false);
   const isStreaming = isUploading || thread.isLoading;
   const handleSubmit = useCallback(
-    (message: Parameters<typeof sendMessage>[1]) => {
+    async (message: Parameters<typeof sendMessage>[1]) => {
       if (isSelectedSkillBootstrapping) {
         return;
       }
@@ -299,6 +316,12 @@ export default function ChatPage() {
         toast.error(t.chatPage.missingThreadIdForSend);
         return;
       }
+      if (isNewThread && safeThreadId) {
+        await threadInitPromiseRef.current;
+      }
+      if (isNewThread && safeThreadId && !isThreadInitReady) {
+        return;
+      }
       setHasSubmitted(true);
       if (safeThreadId && (isNewThread || showWelcomeStyle)) {
         router.replace(`/workspace/chats/${safeThreadId}?is_chatting=true`);
@@ -307,6 +330,7 @@ export default function ChatPage() {
     },
     [
       isNewThread,
+      isThreadInitReady,
       isSelectedSkillBootstrapping,
       router,
       safeThreadId,
@@ -633,14 +657,14 @@ export default function ChatPage() {
                     type: POST_MESSAGE_TYPES.IS_CHATTING,
                     isChatting: false,
                   });
-                  resetNewSessionState();
                   // 始终复用 query 中的 thread_id。
                   const nextQuery = new URLSearchParams();
                   if (threadId && threadId !== "new") {
                     nextQuery.set("thread_id", threadId);
                   }
+                  // /workspace/chats/${threadId}?is_chatting=false
                   router.replace(
-                    `/workspace/chats/${threadId}?is_chatting=false`,
+                    `/workspace/chats/new?thread_id=${threadId}`,
                   );
                 }}
               >