fix: 修复历史消息消失和用户消息重复问题

1. 移除 wrappedSendMessage，避免用户消息 ID 冲突导致重复
2. 添加 initialMessagesRef 保存初始消息，防止历史消息丢失
3. 改进 mergedMessages 逻辑：合并 初始消息 + useChat消息 + appendedMessages
4. 使用 Map 进行去重，按创建时间排序

Co-authored-by: Cursor <cursoragent@cursor.com>

components/chat.tsx

@@ -398,26 +398,15 @@ export function Chat({
     },
   });
 
-  // 🆕 包装 sendMessage，在发送时保存用户消息到 appendedMessages
-  // 这样即使 useChat 重置消息状态，用户消息也会保留在 mergedMessages 中
-  const wrappedSendMessage = useCallback((message: Parameters<typeof sendMessage>[0]) => {
-    // 保存用户消息到 appendedMessages
-    const textPart = message?.parts?.find((p: any) => p.type === "text") as any;
-    const userMessage: ChatMessage = {
-      id: generateUUID(),
-      role: "user",
-      content: textPart?.text || "",
-      createdAt: new Date(),
-      parts: message?.parts || [],
-      attachments: (message as any)?.attachments || [],
-    } as ChatMessage;
-    
-    console.log("[Chat] Saving user message to appendedMessages:", userMessage.id);
-    setAppendedMessages((prev) => [...prev, userMessage]);
-    
-    // 调用原始的 sendMessage
-    return sendMessage(message);
-  }, [sendMessage]);
+  // 🆕 保存 initialMessages 的引用，防止历史消息丢失
+  // 当 useChat 内部状态重置时，我们仍然有初始消息
+  const initialMessagesRef = useRef<ChatMessage[]>(initialMessages);
+  useEffect(() => {
+    // 只在初始化时设置，不在后续更新
+    if (initialMessagesRef.current.length === 0 && initialMessages.length > 0) {
+      initialMessagesRef.current = initialMessages;
+    }
+  }, [initialMessages]);
 
   // 调试：监控聊天状态变化 & 持久化生成状态
   // 使用 ref 来访问最新的 modelsData，避免依赖数组问题
@@ -456,7 +445,7 @@ export function Chat({
 
   useEffect(() => {
     if (query && !hasAppendedQuery) {
-      wrappedSendMessage({
+      sendMessage({
         role: "user" as const,
         parts: [{ type: "text", text: query }],
       });
@@ -1107,21 +1096,38 @@ export function Chat({
     setMessages,
   });
 
-  // 🆕 合并 useChat 的 messages 和 appendedMessages
-  // appendedMessages 包含通过 data-appendMessage 添加的消息
+  // 🆕 合并消息：初始消息 + useChat 消息 + appendedMessages
+  // 确保历史消息不会因为 useChat 内部状态重置而丢失
   const mergedMessages = useMemo(() => {
-    if (appendedMessages.length === 0) {
-      return messages;
-    }
-    // 过滤掉已存在的消息，然后合并
-    const newMessages = appendedMessages.filter(
-      (appended) => !messages.some((m) => m.id === appended.id)
-    );
-    if (newMessages.length > 0) {
-      console.log("[Chat] Rendering with merged messages:", messages.length, "+", newMessages.length);
-      return [...messages, ...newMessages];
-    }
-    return messages;
+    // 使用 Map 进行去重，以 ID 为键
+    const messageMap = new Map<string, ChatMessage>();
+    
+    // 1. 首先添加初始消息（历史记录）
+    initialMessagesRef.current.forEach(m => {
+      messageMap.set(m.id, m);
+    });
+    
+    // 2. 然后添加 useChat 的当前消息（会覆盖相同 ID 的旧消息）
+    messages.forEach(m => {
+      messageMap.set(m.id, m);
+    });
+    
+    // 3. 最后添加 appendedMessages（data-appendMessage 的消息）
+    appendedMessages.forEach(m => {
+      if (!messageMap.has(m.id)) {
+        messageMap.set(m.id, m);
+      }
+    });
+    
+    // 按创建时间排序
+    const result = Array.from(messageMap.values()).sort((a, b) => {
+      const timeA = (a as any).createdAt ? new Date((a as any).createdAt).getTime() : 0;
+      const timeB = (b as any).createdAt ? new Date((b as any).createdAt).getTime() : 0;
+      return timeA - timeB;
+    });
+    
+    console.log("[Chat] Merged messages:", result.length, "(initial:", initialMessagesRef.current.length, ", current:", messages.length, ", appended:", appendedMessages.length, ")");
+    return result;
   }, [messages, appendedMessages]);
 
   return (
@@ -1139,7 +1145,7 @@ export function Chat({
           isReadonly={isReadonly}
           messages={mergedMessages}
           regenerate={regenerate}
-          sendMessage={wrappedSendMessage}
+          sendMessage={sendMessage}
           selectedModelId={currentModelId}
           setMessages={setMessages}
           status={status}
@@ -1169,7 +1175,7 @@ export function Chat({
               onModelChange={setCurrentModelId}
               selectedModelId={currentModelId}
               selectedVisibilityType={visibilityType}
-              sendMessage={wrappedSendMessage}
+              sendMessage={sendMessage}
               setAttachments={setAttachments}
               setInput={setInput}
               setMessages={setMessages}
@@ -1202,7 +1208,7 @@ export function Chat({
         regenerate={regenerate}
         selectedModelId={currentModelId}
         selectedVisibilityType={visibilityType}
-        sendMessage={wrappedSendMessage}
+        sendMessage={sendMessage}
         setAttachments={setAttachments}
         setInput={setInput}
         setMessages={setMessages}