fix(auth): prevent concurrent sendCodeSilently and add edge case tests

apps/lib/features/auth/presentation/cubits/register_cubit.dart

@@ -167,7 +167,7 @@ class RegisterCubit extends Cubit<RegisterState> {
   }
 
   Future<void> sendCodeSilently() async {
-    if (!state.isStep1Valid) return;
+    if (!state.isStep1Valid || state.isSending) return;
 
     emit(state.copyWith(isSending: true));
 

apps/test/features/auth/presentation/cubits/register_cubit_test.dart

@@ -7,6 +7,7 @@ import 'package:social_app/features/auth/data/auth_repository.dart';
 import 'package:social_app/features/auth/data/models/auth_response.dart';
 import 'package:social_app/features/auth/data/models/signup_request.dart';
 import 'package:social_app/features/auth/presentation/cubits/register_cubit.dart';
+import 'package:social_app/core/api/api_exception.dart';
 
 class MockAuthRepository extends Mock implements AuthRepository {}
 
@@ -86,5 +87,62 @@ void main() {
         verify(() => mockRepository.signupStart(any())).called(1);
       },
     );
+
+    blocTest<RegisterCubit, RegisterState>(
+      'restores isSending to false and sets errorMessage on error',
+      build: () => cubit,
+      seed: () => RegisterState(
+        username: const Username.dirty('testuser'),
+        email: const Email.dirty('test@example.com'),
+        password: const Password.dirty('password123'),
+      ),
+      setUp: () {
+        when(
+          () => mockRepository.signupStart(any()),
+        ).thenThrow(ServerException('Network error'));
+      },
+      act: (c) => c.sendCodeSilently(),
+      expect: () => [
+        predicate<RegisterState>((state) => state.isSending == true),
+        predicate<RegisterState>(
+          (state) =>
+              state.isSending == false && state.errorMessage == 'Network error',
+        ),
+      ],
+      verify: (_) {
+        verify(() => mockRepository.signupStart(any())).called(1);
+      },
+    );
+
+    blocTest<RegisterCubit, RegisterState>(
+      'does not call signupStart when input is invalid',
+      build: () => cubit,
+      seed: () => RegisterState(
+        username: const Username.dirty(''),
+        email: const Email.dirty('invalid'),
+        password: const Password.dirty(''),
+      ),
+      act: (c) => c.sendCodeSilently(),
+      expect: () => [],
+      verify: (_) {
+        verifyNever(() => mockRepository.signupStart(any()));
+      },
+    );
+
+    blocTest<RegisterCubit, RegisterState>(
+      'returns early when isSending is true',
+      build: () => cubit,
+      seed: () => RegisterState(
+        username: const Username.dirty('testuser'),
+        email: const Email.dirty('test@example.com'),
+        password: const Password.dirty('password123'),
+        isSending: true,
+      ),
+      act: (c) => c.sendCodeSilently(),
+      expect: () => [],
+      verify: (_) {
+        verifyNever(() => mockRepository.signupStart(any()));
+      },
+    );
   });
 }