fix: 修复考试系统 401 鉴权失败

lib/pages/exam_creation_page.dart

@@ -4,6 +4,7 @@ import 'package:mathmate/pages/exam_taking_page.dart';
 import 'package:mathmate/services/ability_score_service.dart';
 import 'package:mathmate/services/auth_service.dart';
 import 'package:mathmate/services/exam_api.dart';
+import 'package:mathmate/services/login_page.dart';
 
 /// 自由组卷配置页 —— 选择维度、难度、题量后创建考试
 class ExamCreationPage extends StatefulWidget {
@@ -75,6 +76,8 @@ class _ExamCreationPageState extends State<ExamCreationPage> {
   }
 
   Future<void> _startExam() async {
+    if (!await _ensureAuthenticated() || !mounted) return;
+
     if (!_serverAvailable) {
       ScaffoldMessenger.of(context).showSnackBar(
         const SnackBar(content: Text('考试服务不可用，请检查后端是否启动')),
@@ -136,6 +139,24 @@ class _ExamCreationPageState extends State<ExamCreationPage> {
     }
   }
 
+  Future<bool> _ensureAuthenticated() async {
+    final AuthService auth = AuthService();
+    if (auth.isLoggedIn && (auth.token?.isNotEmpty ?? false)) return true;
+
+    ScaffoldMessenger.of(context).showSnackBar(
+      const SnackBar(content: Text('考试功能需要登录，请先完成登录')),
+    );
+    final bool? loggedIn = await Navigator.of(context).push<bool>(
+      MaterialPageRoute(
+        builder: (_) => const LoginPage(returnToPreviousPage: true),
+      ),
+    );
+    if (!mounted) return false;
+    return loggedIn == true &&
+        auth.isLoggedIn &&
+        (auth.token?.isNotEmpty ?? false);
+  }
+
   List<String>? _boardsForSelectedDimension() {
     final String? dimension = _selectedDimension;
     if (dimension == null) return null;

lib/services/auth_service.dart

@@ -1,6 +1,5 @@
 import 'dart:convert';
 
-import 'package:flutter/foundation.dart' show kIsWeb, kReleaseMode;
 import 'package:flutter_dotenv/flutter_dotenv.dart';
 import 'package:http/http.dart' as http;
 import 'package:shared_preferences/shared_preferences.dart';
@@ -47,23 +46,20 @@ class AuthResponse {
   final String? error;
 
   AuthResponse({this.token, this.user, this.error});
-  bool get ok => token != null;
+  bool get ok => token != null || user != null;
 }
 
 /// 认证服务 —— 注册/登录/个人信息/Token 管理。
 ///
 /// 与服务端 auth_server.js 通信，Token 存储在 SharedPreferences。
 class AuthService {
-  // 公开构建通过 AUTH_BASE_URL 指向生产服务；本地开发仍保留原调试地址。
+  // 默认与考试接口使用同一套线上用户和签名密钥；本地联调可显式配置地址。
   static String get _baseUrl {
     final configured = (dotenv.env['AUTH_BASE_URL'] ?? '').trim();
     if (configured.isNotEmpty) {
       return configured.replaceFirst(RegExp(r'/+$'), '');
     }
-    if (kReleaseMode) return 'https://mathmate.top/api/auth';
-    return kIsWeb
-        ? 'http://localhost:3002/api/auth'
-        : 'http://10.136.66.36:3002/api/auth';
+    return 'https://mathmate.top/api/auth';
   }
 
   static const String _tokenKey = 'auth_token';

lib/services/exam_api.dart

@@ -162,6 +162,9 @@ class ExamApi {
     if (response.statusCode >= 200 && response.statusCode < 300) {
       return decoded as Map<String, dynamic>;
     }
+    if (response.statusCode == 401) {
+      throw ExamApiException(401, '登录状态已失效，请重新登录');
+    }
     final message = decoded is Map<String, dynamic>
         ? decoded['detail']
         : decoded;

lib/services/login_page.dart

@@ -4,7 +4,10 @@ import 'package:flutter/material.dart';
 import '../services/auth_service.dart'; 
 
 class LoginPage extends StatefulWidget {
-  const LoginPage({super.key});
+  /// 从业务页进入登录时，登录成功后返回原页，而不是重复创建主页面。
+  final bool returnToPreviousPage;
+
+  const LoginPage({super.key, this.returnToPreviousPage = false});
 
   @override
   State<LoginPage> createState() => _LoginPageState();
@@ -14,7 +17,7 @@ class _LoginPageState extends State<LoginPage> {
   final _formKey = GlobalKey<FormState>();
   final _usernameController = TextEditingController();
   final _passwordController = TextEditingController();
-  
+
   bool _obscurePassword = true; 
   bool _isLoading = false;      
 
@@ -35,9 +38,8 @@ class _LoginPageState extends State<LoginPage> {
         password: _passwordController.text.trim(),
       );
 
-      setState(() => _isLoading = false);
-
       if (!mounted) return;
+      setState(() => _isLoading = false);
 
       if (response.ok) {
         ScaffoldMessenger.of(context).showSnackBar(
@@ -46,16 +48,19 @@ class _LoginPageState extends State<LoginPage> {
             backgroundColor: Colors.green,
           ),
         );
-
-        // 登录成功后，销毁登录页，跳转到 MathMate 主界面
-        Navigator.of(context).pushReplacement(
-          MaterialPageRoute(builder: (context) => const MainScreen()),
-        );
-
+
+        if (widget.returnToPreviousPage) {
+          Navigator.of(context).pop(true);
+        } else {
+          // 启动登录成功后，销毁登录页并进入主界面。
+          Navigator.of(context).pushReplacement(
+            MaterialPageRoute(builder: (context) => const MainScreen()),
+          );
+        }
       } else {
         ScaffoldMessenger.of(context).showSnackBar(
           SnackBar(
-            content: Text(response.error ?? '登录失败，请检查账号密码'), 
+            content: Text(response.error ?? '登录失败，请检查账号密码'),
             backgroundColor: Colors.red,
           ),
         );
@@ -76,10 +81,14 @@ class _LoginPageState extends State<LoginPage> {
           // 右上角的跳过按钮
           TextButton(
             onPressed: () {
-              // 点击跳过，直接以游客身份进入主界面，且无法返回登录页
-              Navigator.of(context).pushReplacement(
-                MaterialPageRoute(builder: (context) => const MainScreen()),
-              );
+              if (widget.returnToPreviousPage) {
+                Navigator.of(context).pop(false);
+              } else {
+                // 点击跳过，直接以游客身份进入主界面，且无法返回登录页
+                Navigator.of(context).pushReplacement(
+                  MaterialPageRoute(builder: (context) => const MainScreen()),
+                );
+              }
             },
             child: const Text(
               '跳过，直接使用',
@@ -189,4 +198,4 @@ const Image(
       ),
     );
   }
-}
+}

test/exam_api_test.dart

@@ -60,4 +60,28 @@ void main() {
 
     expect(count, 2);
   });
+
+  test('protected requests report an actionable message for 401', () async {
+    final client = MockClient(
+      (_) async => http.Response(
+        '{"detail":"Valid Bearer token required"}',
+        401,
+        headers: {'content-type': 'application/json'},
+      ),
+    );
+    final api = ExamApi(
+      baseUrl: 'https://example.test',
+      client: client,
+      tokenProvider: () => null,
+    );
+
+    await expectLater(
+      api.availableQuestionCount(),
+      throwsA(
+        isA<ExamApiException>()
+            .having((e) => e.statusCode, 'statusCode', 401)
+            .having((e) => e.message, 'message', '登录状态已失效，请重新登录'),
+      ),
+    );
+  });
 }