feat(app): 班级码验证前后端联调 — AuthBloc接入API + 错误计数锁定UI

app/lib/features/auth/bloc/auth_bloc.dart

@@ -4,6 +4,7 @@
 //                                     ↕
 //                                  Authenticating → Authenticated/AuthError
 
+import 'package:dio/dio.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:logger/logger.dart';
 
@@ -11,6 +12,7 @@ import '../../../data/models/auth_token.dart';
 import '../../../data/models/user.dart';
 import '../../../data/remote/api_client.dart';
 import '../../../data/repositories/auth_repository.dart';
+import '../../../data/repositories/class_repository.dart';
 
 part 'auth_event.dart';
 part 'auth_state.dart';
@@ -18,10 +20,14 @@ part 'auth_state.dart';
 /// 认证 BLoC — 处理所有认证相关的状态转换
 class AuthBloc extends Bloc<AuthEvent, AuthState> {
   final AuthRepository _authRepository;
+  final ClassRepository? _classRepository;
   final Logger _logger = Logger(printer: PrettyPrinter(methodCount: 0));
 
-  AuthBloc({required AuthRepository authRepository})
-      : _authRepository = authRepository,
+  AuthBloc({
+    required AuthRepository authRepository,
+    ClassRepository? classRepository,
+  })  : _authRepository = authRepository,
+        _classRepository = classRepository,
         super(const AuthInitial()) {
     // 注册事件处理器
     on<AppStarted>(_onAppStarted);
@@ -138,13 +144,64 @@ class AuthBloc extends Bloc<AuthEvent, AuthState> {
     final currentState = state;
     if (currentState is! Authenticated) return;
 
-    // TODO: 调用后端 API 验证班级码并加入班级
-    // 当前先标记为已完成，班级码验证在 F8 阶段完善
-    emit(currentState.copyWith(
-      needsClassCode: false,
-    ));
+    // 如果没有 ClassRepository（离线模式），直接跳过
+    final classRepo = _classRepository;
+    if (classRepo == null) {
+      _logger.w('ClassRepository 不可用，跳过班级码验证');
+      emit(currentState.copyWith(needsClassCode: false));
+      return;
+    }
 
-    _logger.i('班级码加入: ${event.classCode}');
+    emit(currentState.copyWith(isLoading: true));
+
+    try {
+      // 调用后端 API 验证班级码并加入班级
+      await classRepo.joinClass(
+        event.classCode,
+        nickname: currentState.user.displayName,
+      );
+
+      // 成功 — 清除班级码需求
+      emit(currentState.copyWith(
+        needsClassCode: false,
+        isLoading: false,
+      ));
+
+      _logger.i('班级码加入成功: ${event.classCode}');
+    } on DioException catch (e) {
+      final statusCode = e.response?.statusCode;
+      String errorMessage = '加入班级失败，请重试';
+
+      if (statusCode == 400) {
+        // 班级码无效或已过期
+        final body = e.response?.data;
+        if (body is Map && body['message'] is String) {
+          errorMessage = body['message'] as String;
+        } else {
+          errorMessage = '班级码无效，请检查后重新输入';
+        }
+      } else if (statusCode == 429) {
+        // 尝试次数过多 — 锁定
+        errorMessage = '尝试次数过多，请等待 30 分钟后再试';
+      }
+
+      _logger.w('班级码验证失败 ($statusCode): $errorMessage');
+      emit(currentState.copyWith(
+        isLoading: false,
+        classCodeError: errorMessage,
+      ));
+    } on OfflineException {
+      emit(currentState.copyWith(
+        isLoading: false,
+        classCodeError: '网络不可用，请检查网络后重试',
+      ));
+    } catch (e) {
+      _logger.e('班级码验证异常: $e');
+      emit(currentState.copyWith(
+        isLoading: false,
+        classCodeError: '加入班级失败，请稍后重试',
+      ));
+    }
   }
 
   /// 用户登出

app/lib/features/auth/bloc/auth_state.dart

@@ -40,21 +40,33 @@ final class Authenticated extends AuthState {
   /// 是否需要班级码加入（学生/家长角色）
   final bool needsClassCode;
 
+  /// 是否正在加载（班级码验证中）
+  final bool isLoading;
+
+  /// 班级码验证错误信息
+  final String? classCodeError;
+
   const Authenticated({
     required this.user,
     this.needsRoleSelection = false,
     this.needsClassCode = false,
+    this.isLoading = false,
+    this.classCodeError,
   });
 
   Authenticated copyWith({
     User? user,
     bool? needsRoleSelection,
     bool? needsClassCode,
+    bool? isLoading,
+    String? classCodeError,
   }) =>
       Authenticated(
         user: user ?? this.user,
         needsRoleSelection: needsRoleSelection ?? this.needsRoleSelection,
         needsClassCode: needsClassCode ?? this.needsClassCode,
+        isLoading: isLoading ?? this.isLoading,
+        classCodeError: classCodeError,
       );
 }