Integrate email notifications into signup and login (#38)

frontend/app/test/auth_services_test.dart

@@ -4,6 +4,8 @@ import 'package:flutter/material.dart';
 
 import 'package:flutter_test/flutter_test.dart';
 
+import 'package:go_router/go_router.dart';
+
 import 'package:sxchnge_auth/sxchnge_auth.dart';
 
 import 'package:sxchnge_app/main.dart';
@@ -21,7 +23,63 @@ class ControlledLogin implements LoginService {
   }
 }
 
+class UnverifiedBackend extends BackendAuthServices {
+  UnverifiedBackend()
+    : super(baseUri: Uri.parse('https://api.example/api/v1'), clientId: 'web');
+  int sends = 0;
+  @override
+  Future<AuthResult> login(LoginRequest request) async =>
+      throw const AuthException(AuthError.accountNotVerified);
+  @override
+  Future<VerificationResult> send({
+    required String email,
+    required String locale,
+  }) async {
+    sends++;
+    return const VerificationResult(isSimulated: false);
+  }
+}
+
 void main() {
+  testWidgets('backend mode gates workspace and recovers unverified login', (
+    tester,
+  ) async {
+    tester.view.physicalSize = const Size(1440, 1200);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+    final backend = UnverifiedBackend();
+    await tester.pumpWidget(SxchngeApp(backend: backend));
+    await tester.pumpAndSettle();
+    final router = GoRouter.of(
+      tester.element(find.byKey(const ValueKey('email'))),
+    );
+    router.go('/accounts');
+    await tester.pumpAndSettle();
+    expect(router.routeInformationProvider.value.uri.path, '/');
+    await tester.enterText(
+      find.byKey(const ValueKey('email')),
+      'user@example.com',
+    );
+    await tester.enterText(
+      find.byKey(const ValueKey('password')),
+      'password-value',
+    );
+    await tester.ensureVisible(find.byKey(const ValueKey('submit')));
+    await tester.tap(find.byKey(const ValueKey('submit')));
+    await tester.pumpAndSettle();
+    expect(
+      router.routeInformationProvider.value.uri.path,
+      '/verification-sent',
+    );
+    expect(backend.sends, 1);
+    expect(
+      find.textContaining('a verification email is on its way'),
+      findsOneWidget,
+    );
+    expect(tester.takeException(), isNull);
+  });
+
   testWidgets(
     'app shows loading, localized failure, and retries through injected service',
     (tester) async {