fix(web): 修复流式期间消息重渲染、WebSocket 无谓重连与新消息计数错误

- MessageBubble 用 React.memo 包裹，流式 delta 只追加到最后一条消息，
  其余消息引用不变可被 memo 跳过，避免 N-1 条历史消息无谓重渲染
- useWebSocket 用 useRef 存储回调最新引用，connect 不再依赖回调引用，
  避免调用方回调变化触发 disconnect+connect 重连
- MessageList 用 prevMessageCountRef 追踪消息条数变化，仅当真正新增
  消息条数时才累加 newMessageCount；流式 delta 不增加条数不再误计数，
  滑到底部按钮触发的清零路径与时序经审查覆盖各种边界场景

web/src/components/Chat/MessageBubble.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useState, useEffect, memo } from 'react';
 import {
   User,
   Bot,
@@ -349,7 +349,7 @@ function parseTaskResult(content: string): TaskToolResult | null {
   }
 }
 
-export function MessageBubble({
+export const MessageBubble = memo(function MessageBubble({
   message,
   onNavigateToSubAgent,
   showThinking = true,
@@ -964,4 +964,4 @@ export function MessageBubble({
       {lightboxElement}
     </div>
   );
-}
+});

web/src/components/Chat/MessageList.tsx

@@ -28,6 +28,11 @@ export function MessageList({
   const viewKeyRef = useRef(viewKey);
   viewKeyRef.current = viewKey;
 
+  // 追踪上次的消息条数，用于计算真正新增的消息数（而非 messages 引用变化次数）。
+  // 流式输出时每个 delta 都会产生新的 messages 数组引用，但消息条数不变，
+  // 不应计入 newMessageCount。
+  const prevMessageCountRef = useRef(messages.length);
+
   // Per-view scroll position memory
   const scrollPositionsRef = useRef<Map<string, number>>(new Map());
 
@@ -86,11 +91,13 @@ export function MessageList({
 
     if (messages.length === 0) {
       isAtBottomRef.current = true;
+      prevMessageCountRef.current = 0;
       return;
     }
 
     if (viewChanged) {
       // View switched (e.g. breadcrumb navigation): restore saved scroll position
+      prevMessageCountRef.current = messages.length;
       const key = viewKey ?? '';
       const savedPos = scrollPositionsRef.current.get(key);
       if (savedPos !== undefined && containerRef.current) {
@@ -108,11 +115,18 @@ export function MessageList({
 
     // Same view, messages changed: normal auto-scroll logic
     const lastMessage = messages[messages.length - 1];
+    const newCount = messages.length - prevMessageCountRef.current;
+    prevMessageCountRef.current = messages.length;
 
     if (lastMessage.role === 'user' || isAtBottomRef.current) {
       bottomRef.current?.scrollIntoView({ behavior: 'instant' });
-    } else {
-      setNewMessageCount((prev) => prev + 1);
+      // 用户自己发消息或已在底部时，不需要计数
+      if (newCount > 0) {
+        setNewMessageCount(0);
+      }
+    } else if (newCount > 0) {
+      // 只有真正新增了消息条数时才累加（流式 delta 不增加条数，不计数）
+      setNewMessageCount((prev) => prev + newCount);
     }
   }, [messages, viewKey]);
 

web/src/hooks/useWebSocket.ts

@@ -39,6 +39,17 @@ export function useWebSocket({
   const isManualDisconnectRef = useRef(false);
   const pingIntervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
 
+  // 用 ref 存储回调的最新引用，避免回调变化导致 connect 重建 → useEffect 重跑 → 无谓断连重连。
+  // 调用方即使未 useCallback 包裹回调，也不会触发重连。
+  const onMessageRef = useRef(onMessage);
+  const onConnectRef = useRef(onConnect);
+  const onDisconnectRef = useRef(onDisconnect);
+  const onErrorRef = useRef(onError);
+  onMessageRef.current = onMessage;
+  onConnectRef.current = onConnect;
+  onDisconnectRef.current = onDisconnect;
+  onErrorRef.current = onError;
+
   const clearPing = useCallback(() => {
     if (pingIntervalRef.current) {
       clearInterval(pingIntervalRef.current);
@@ -73,13 +84,13 @@ export function useWebSocket({
             }
           }
         }, PING_INTERVAL_MS);
-        onConnect?.();
+        onConnectRef.current?.();
       };
 
       ws.onmessage = (event) => {
         try {
           const message = JSON.parse(event.data) as WsOutbound;
-          onMessage?.(message);
+          onMessageRef.current?.(message);
         } catch (error) {
           console.error('Failed to parse message:', error);
         }
@@ -87,13 +98,13 @@ export function useWebSocket({
 
       ws.onerror = (error) => {
         setStatus('error');
-        onError?.(error);
+        onErrorRef.current?.(error);
       };
 
       ws.onclose = () => {
         setStatus('disconnected');
         clearPing();
-        onDisconnect?.();
+        onDisconnectRef.current?.();
 
         // 指数退避自动重连：3s → 6s → 12s → 24s → 60s 封顶
         if (!isManualDisconnectRef.current && reconnectAttemptsRef.current < maxReconnectAttempts) {
@@ -109,7 +120,7 @@ export function useWebSocket({
       setStatus('error');
       console.error('WebSocket connection error:', error);
     }
-  }, [url, onMessage, onConnect, onDisconnect, onError, reconnectInterval, maxReconnectAttempts, clearPing]);
+  }, [url, reconnectInterval, maxReconnectAttempts, clearPing]);
 
   const disconnect = useCallback(() => {
     isManualDisconnectRef.current = true;