feat: 前端 401 拦截器 — access token 过期时自动刷新并重试原请求

api.ts:
- 增加 setAuthCallbacks 回调注入机制（避免 api/auth 循环依赖）
- request() 对非公开路径自动附加 Authorization header
- 收到 401 时自动触发 refresh token 刷新，成功后重试原请求
- 并发保护：多个 401 只触发一次 refresh，其余等待同一 Promise
- refreshTokenDirect 内部方法绕过 401 拦截避免递归

auth.tsx:
- 用 ref 保存 persistAuth/scheduleRefresh 最新引用（避免闭包陈旧）
- 初始化时调用 setAuthCallbacks 注入认证回调

frontend/src/lib/api.ts

@@ -1,6 +1,7 @@
 // ============================================================
 // HTTP API 客户端
 // 职责：封装 REST API 请求（auth、conversations 等）
+//       内置 401 拦截 + 自动刷新 + 重试机制
 // ============================================================
 
 const API_BASE = "/api";
@@ -11,9 +12,69 @@ interface ApiResponse<T> {
   status: number;
 }
 
+// ---- 认证回调（由 AuthProvider 注入，避免循环依赖） ----
+
+interface AuthCallbacks {
+  getAccessToken: () => string | null;
+  getRefreshToken: () => string | null;
+  onRefreshSuccess: (user: AuthUser, accessToken: string, refreshToken: string) => void;
+  onRefreshFailed: () => void;
+}
+
+let authCallbacks: AuthCallbacks | null = null;
+let refreshPromise: Promise<boolean> | null = null;
+
+/** 由 AuthProvider 在初始化时调用，注入认证回调。 */
+export function setAuthCallbacks(callbacks: AuthCallbacks): void {
+  authCallbacks = callbacks;
+}
+
+/** 不需要认证的公开路径。 */
+const PUBLIC_PATHS = new Set([
+  "/auth/register",
+  "/auth/login",
+  "/auth/refresh",
+]);
+
+function isPublicPath(path: string): boolean {
+  return PUBLIC_PATHS.has(path);
+}
+
+/** 尝试用 refresh token 换取新的 access token。 */
+async function doRefresh(): Promise<boolean> {
+  const rt = authCallbacks?.getRefreshToken();
+  if (!rt) return false;
+
+  const res = await refreshTokenDirect(rt);
+  if (res.data) {
+    authCallbacks?.onRefreshSuccess(
+      res.data.user,
+      res.data.access_token,
+      res.data.refresh_token
+    );
+    return true;
+  }
+
+  authCallbacks?.onRefreshFailed();
+  return false;
+}
+
+/** 带并发保护的刷新：多个 401 只触发一次 refresh。 */
+async function refreshWithLock(): Promise<boolean> {
+  if (!refreshPromise) {
+    refreshPromise = doRefresh().finally(() => {
+      refreshPromise = null;
+    });
+  }
+  return refreshPromise;
+}
+
+// ---- 核心请求函数 ----
+
 async function request<T>(
   path: string,
-  options: RequestInit = {}
+  options: RequestInit = {},
+  _retry = false
 ): Promise<ApiResponse<T>> {
   const url = `${API_BASE}${path}`;
   const headers: Record<string, string> = {
@@ -21,6 +82,14 @@ async function request<T>(
     ...(options.headers as Record<string, string>),
   };
 
+  // 对非公开路径自动附加 access token
+  if (!isPublicPath(path) && !headers["Authorization"]) {
+    const token = authCallbacks?.getAccessToken();
+    if (token) {
+      headers["Authorization"] = `Bearer ${token}`;
+    }
+  }
+
   try {
     const res = await fetch(url, { ...options, headers });
     const status = res.status;
@@ -31,6 +100,14 @@ async function request<T>(
 
     const body = await res.json();
 
+    // 401 拦截：尝试刷新 token 后重试（仅重试一次）
+    if (res.status === 401 && !_retry && !isPublicPath(path) && authCallbacks) {
+      const refreshed = await refreshWithLock();
+      if (refreshed) {
+        return request<T>(path, options, true);
+      }
+    }
+
     if (!res.ok) {
       return {
         error: { code: body.error || "UNKNOWN", message: body.message || "请求失败" },
@@ -85,6 +162,33 @@ export async function login(
   });
 }
 
+/** 内部用的 refresh 请求，不经过 401 拦截（避免递归）。 */
+async function refreshTokenDirect(
+  refresh_token: string
+): Promise<ApiResponse<AuthResponse>> {
+  const url = `${API_BASE}/auth/refresh`;
+  try {
+    const res = await fetch(url, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ refresh_token }),
+    });
+    const body = await res.json();
+    if (!res.ok) {
+      return {
+        error: { code: body.error || "UNKNOWN", message: body.message || "请求失败" },
+        status: res.status,
+      };
+    }
+    return { data: body as AuthResponse, status: res.status };
+  } catch {
+    return {
+      error: { code: "NETWORK_ERROR", message: "网络连接失败" },
+      status: 0,
+    };
+  }
+}
+
 export async function refreshToken(
   refresh_token: string
 ): Promise<ApiResponse<AuthResponse>> {
@@ -96,11 +200,11 @@ export async function refreshToken(
 
 export async function logout(
   accessToken: string,
-  refreshToken: string
+  refreshTokenStr: string
 ): Promise<ApiResponse<{ message: string }>> {
   return request<{ message: string }>("/auth/logout", {
     method: "POST",
     headers: authHeaders(accessToken),
-    body: JSON.stringify({ refresh_token: refreshToken }),
+    body: JSON.stringify({ refresh_token: refreshTokenStr }),
   });
 }