fix: 修复白屏 — SW networkFirst + initSession try/catch + Error Boundary

1. sw.js: /index.html 导航请求使用 networkFirst 策略替代 cacheFirst，
   避免旧 SW 缓存不存在的旧 hash 资源导致 404 白屏
2. App.tsx: initSession 添加 try/catch 异常保护，防止初始化
   失败导致整个 React 树崩溃
3. 新建 ErrorBoundary.tsx: React 错误边界组件，捕获渲染异常
   显示友好错误页面而非白屏

frontend/web/src/App.tsx

@@ -2,6 +2,7 @@ import { useState, useEffect, useCallback, useRef } from 'react';
 import { AppLayout } from '@/components/layout/AppLayout';
 import { ChatContainer } from '@/components/chat/ChatContainer';
 import { ChatInput } from '@/components/chat/ChatInput';
+import { ErrorBoundary } from '@/components/ErrorBoundary';
 import { useAuth } from '@/hooks/useAuth';
 import { useChat } from '@/hooks/useChat';
 import { useSessionStore, isAdminUser } from '@/store/sessionStore';
@@ -58,67 +59,73 @@ export default function App() {
     if (!userId || initializedRef.current) return;
     initializedRef.current = true;
 
-    const admin = isAdminUser(userId);
+    try {
+      const admin = isAdminUser(userId);
 
-    // 1. 从服务端加载会话列表
-    await loadSessionsFromServer(userId);
-    const currentSessions = useSessionStore.getState().sessions;
+      // 1. 从服务端加载会话列表
+      await loadSessionsFromServer(userId);
+      const currentSessions = useSessionStore.getState().sessions;
 
-    // 2. 检查 URL hash
-    const hashId = getSessionIdFromHash();
+      // 2. 检查 URL hash
+      const hashId = getSessionIdFromHash();
 
-    if (hashId) {
-      // 尝试加载 hash 指定的会话
-      const found = currentSessions.find((s) => s.id === hashId);
-      if (found) {
-        setCurrentSessionId(found.id);
-        setHashSessionId(found.id);
-        await loadMessagesFromServer(found.id);
-        return;
-      }
-      // 会话可能已被删除，尝试从 API 获取消息（404 时 catch）
-      try {
-        const resp = await fetchMessages(hashId);
-        if (resp.messages && resp.messages.length > 0) {
-          // 消息存在说明会话仍有效（虽然不在列表里，可能是刚创建的）
-          setCurrentSessionId(hashId);
-          setHashSessionId(hashId);
-          const msgs = resp.messages.map((m: any, i: number) => ({
-            id: m.id ? String(m.id) : `hist_${i}_${Date.now()}`,
-            role: m.role,
-            content: m.content,
-            timestamp: typeof m.created_at === 'number' ? m.created_at : Date.now(),
-            isStreaming: false,
-          }));
-          setMessages(msgs);
-          useChatStore.getState().setMessages(msgs);
+      if (hashId) {
+        // 尝试加载 hash 指定的会话
+        const found = currentSessions.find((s) => s.id === hashId);
+        if (found) {
+          setCurrentSessionId(found.id);
+          setHashSessionId(found.id);
+          await loadMessagesFromServer(found.id);
           return;
         }
-      } catch {
-        // 会话不存在，回退
+        // 会话可能已被删除，尝试从 API 获取消息（404 时 catch）
+        try {
+          const resp = await fetchMessages(hashId);
+          if (resp.messages && resp.messages.length > 0) {
+            // 消息存在说明会话仍有效（虽然不在列表里，可能是刚创建的）
+            setCurrentSessionId(hashId);
+            setHashSessionId(hashId);
+            const msgs = resp.messages.map((m: any, i: number) => ({
+              id: m.id ? String(m.id) : `hist_${i}_${Date.now()}`,
+              role: m.role,
+              content: m.content,
+              timestamp: typeof m.created_at === 'number' ? m.created_at : Date.now(),
+              isStreaming: false,
+            }));
+            setMessages(msgs);
+            useChatStore.getState().setMessages(msgs);
+            return;
+          }
+        } catch {
+          // 会话不存在，回退
+        }
+        // 回退：清除 hash，加载最新/主对话
+        setHashSessionId(null);
       }
-      // 回退：清除 hash，加载最新/主对话
-      setHashSessionId(null);
-    }
 
-    // 3. 无 hash 或 hash 无效：加载最新会话
-    if (admin) {
-      // 管理员：确保主对话存在
-      const mainSession = await ensureMainSession(userId);
-      if (mainSession) {
-        setCurrentSessionId(mainSession.id);
-        setHashSessionId(mainSession.id);
-        await loadMessagesFromServer(mainSession.id);
-        return;
+      // 3. 无 hash 或 hash 无效：加载最新会话
+      if (admin) {
+        // 管理员：确保主对话存在
+        const mainSession = await ensureMainSession(userId);
+        if (mainSession) {
+          setCurrentSessionId(mainSession.id);
+          setHashSessionId(mainSession.id);
+          await loadMessagesFromServer(mainSession.id);
+          return;
+        }
       }
-    }
 
-    // 普通用户：选择最新会话
-    if (currentSessions.length > 0) {
-      const latest = currentSessions[0]; // 已按 updated_at DESC 排序
-      setCurrentSessionId(latest.id);
-      setHashSessionId(latest.id);
-      await loadMessagesFromServer(latest.id);
+      // 普通用户：选择最新会话
+      if (currentSessions.length > 0) {
+        const latest = currentSessions[0]; // 已按 updated_at DESC 排序
+        setCurrentSessionId(latest.id);
+        setHashSessionId(latest.id);
+        await loadMessagesFromServer(latest.id);
+      }
+    } catch (error) {
+      console.error('[App] initSession failed:', error);
+      // 重置状态避免死锁，允许后续重试
+      initializedRef.current = false;
     }
   }, [userId, loadSessionsFromServer, ensureMainSession, setCurrentSessionId, setMessages, loadMessagesFromServer]);
 
@@ -317,13 +324,15 @@ export default function App() {
 
   // 聊天界面
   return (
-    <AppLayout>
-      <div className="flex flex-col h-full overflow-hidden">
-        <div className="flex-1 min-h-0 overflow-hidden">
-          <ChatContainer />
+    <ErrorBoundary>
+      <AppLayout>
+        <div className="flex flex-col h-full overflow-hidden">
+          <div className="flex-1 min-h-0 overflow-hidden">
+            <ChatContainer />
+          </div>
+          <ChatInput onSend={send} />
         </div>
-        <ChatInput onSend={send} />
-      </div>
-    </AppLayout>
+      </AppLayout>
+    </ErrorBoundary>
   );
 }

frontend/web/src/components/ErrorBoundary.tsx

@@ -0,0 +1,61 @@
+import React, { Component, ErrorInfo, ReactNode } from 'react'
+
+interface Props {
+  children: ReactNode
+  fallback?: ReactNode
+}
+
+interface State {
+  hasError: boolean
+  error: Error | null
+}
+
+export class ErrorBoundary extends Component<Props, State> {
+  constructor(props: Props) {
+    super(props)
+    this.state = { hasError: false, error: null }
+  }
+
+  static getDerivedStateFromError(error: Error): State {
+    return { hasError: true, error }
+  }
+
+  componentDidCatch(error: Error, errorInfo: ErrorInfo) {
+    console.error('[ErrorBoundary] Caught error:', error, errorInfo)
+  }
+
+  handleReset = () => {
+    this.setState({ hasError: false, error: null })
+  }
+
+  render() {
+    if (this.state.hasError) {
+      if (this.props.fallback) return this.props.fallback
+      return (
+        <div style={{
+          display: 'flex', flexDirection: 'column', alignItems: 'center',
+          justifyContent: 'center', height: '100vh', padding: '2rem',
+          background: '#0f172a', color: '#e2e8f0', fontFamily: 'system-ui'
+        }}>
+          <h1 style={{ fontSize: '1.5rem', marginBottom: '0.5rem' }}>⚠️ 应用遇到错误</h1>
+          <p style={{ color: '#94a3b8', marginBottom: '1rem', maxWidth: '400px', textAlign: 'center' }}>
+            {this.state.error?.message || '未知错误'}
+          </p>
+          <button
+            onClick={this.handleReset}
+            style={{
+              padding: '0.5rem 1.5rem', borderRadius: '0.5rem',
+              background: '#3b82f6', color: 'white', border: 'none',
+              cursor: 'pointer', fontSize: '0.875rem'
+            }}
+          >
+            重试
+          </button>
+        </div>
+      )
+    }
+    return this.props.children
+  }
+}
+
+export default ErrorBoundary