Deliver localized auth app with verification and go_router

Integrate themed login/signup, EN/RU localization, shared dummy providers, verification recovery screens and named URL routes. Store frontend guidelines, workflow skills, validation and delivery documentation. Related to #2, #3, #5 and #6.

frontend/app/test/routing_test.dart

@@ -0,0 +1,157 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:go_router/go_router.dart';
+
+import 'package:provider/provider.dart';
+
+import 'package:sxchnge_auth/sxchnge_auth.dart';
+
+import 'package:sxchnge_app/main.dart';
+import 'package:sxchnge_app/providers/locale.dart';
+import 'package:sxchnge_app/routing/routes.dart';
+import 'package:sxchnge_app/verification/page.dart';
+
+class PendingConfirmation implements VerificationService {
+  final results = <String, Completer<VerificationResult>>{};
+  @override
+  Future<VerificationResult> confirm({required String token}) =>
+      (results[token] = Completer<VerificationResult>()).future;
+  @override
+  Future<VerificationResult> send({
+    required String email,
+    required String locale,
+  }) async => const VerificationResult(isSimulated: true);
+}
+
+Future<GoRouter> openRoute(
+  WidgetTester tester,
+  String route, {
+  VerificationService service = const DummyVerificationService(
+    delay: Duration.zero,
+  ),
+}) async {
+  tester.platformDispatcher.defaultRouteNameTestValue = route;
+  addTearDown(tester.platformDispatcher.clearDefaultRouteNameTestValue);
+  await tester.pumpWidget(SxchngeApp(verificationService: service));
+  await tester.pump();
+  return GoRouter.of(tester.element(find.byType(Scaffold).last));
+}
+
+void main() {
+  testWidgets('unknown deep link redirects to canonical login URL', (
+    tester,
+  ) async {
+    final router = await openRoute(tester, '/unknown?token=private');
+    await tester.pumpAndSettle();
+    expect(router.routeInformationProvider.value.uri.toString(), '/');
+    expect(find.byKey(const ValueKey('email')), findsOneWidget);
+  });
+
+  testWidgets(
+    'changing confirmation token ignores the previous pending result',
+    (tester) async {
+      final service = PendingConfirmation();
+      final router = await openRoute(
+        tester,
+        '/verify-email?token=first',
+        service: service,
+      );
+      await tester.pump();
+      expect(service.results.containsKey('first'), isTrue);
+      router.goNamed(
+        AppRoutes.verifyEmail,
+        queryParameters: {'token': 'second'},
+      );
+      await tester.pump();
+      await tester.pump();
+      service.results['second']!.completeError(
+        const VerificationException(VerificationError.expired),
+      );
+      await tester.pumpAndSettle();
+      expect(
+        find.byKey(const ValueKey('verification-expired')),
+        findsOneWidget,
+      );
+      service.results['first']!.complete(
+        const VerificationResult(isSimulated: true),
+      );
+      await tester.pumpAndSettle();
+      expect(
+        find.byKey(const ValueKey('verification-expired')),
+        findsOneWidget,
+      );
+      expect(find.byKey(const ValueKey('verification-verified')), findsNothing);
+    },
+  );
+
+  testWidgets(
+    'platform back and forward route updates recheck confirmation tokens',
+    (tester) async {
+      final router = await openRoute(tester, '/verify-email?token=demo-valid');
+      await tester.pumpAndSettle();
+      await router.routeInformationProvider.didPushRouteInformation(
+        RouteInformation(uri: Uri.parse('/verify-email?token=demo-expired')),
+      );
+      await tester.pumpAndSettle();
+      expect(
+        find.byKey(const ValueKey('verification-expired')),
+        findsOneWidget,
+      );
+      await router.routeInformationProvider.didPushRouteInformation(
+        RouteInformation(uri: Uri.parse('/verify-email?token=demo-valid')),
+      );
+      await tester.pumpAndSettle();
+      expect(
+        find.byKey(const ValueKey('verification-verified')),
+        findsOneWidget,
+      );
+      expect(
+        router.routeInformationProvider.value.uri.queryParameters['token'],
+        'demo-valid',
+      );
+    },
+  );
+
+  testWidgets('locale rebuild preserves router, URL and confirmation state', (
+    tester,
+  ) async {
+    final router = await openRoute(tester, '/verify-email?token=demo-valid');
+    await tester.pumpAndSettle();
+    final context = tester.element(find.byType(VerificationPage));
+    await context.read<LocaleProvider>().setLocale(const Locale('ru'));
+    await tester.pumpAndSettle();
+    expect(
+      GoRouter.of(tester.element(find.byType(VerificationPage))),
+      same(router),
+    );
+    expect(find.byKey(const ValueKey('verification-verified')), findsOneWidget);
+    expect(find.text('Ваша почта\nподтверждена.'), findsOneWidget);
+  });
+
+  testWidgets(
+    'signup email stays in memory and is excluded from serialized history',
+    (tester) async {
+      final router = await openRoute(tester, '/');
+      await tester.pumpAndSettle();
+      router.goNamed(AppRoutes.verificationSent, extra: 'alex@example.com');
+      await tester.pumpAndSettle();
+      expect(find.text('alex@example.com'), findsOneWidget);
+      expect(find.byKey(const ValueKey('verification-sent')), findsOneWidget);
+      final restored = router.routeInformationParser.restoreRouteInformation(
+        router.routerDelegate.currentConfiguration,
+      )!;
+      expect(restored.state.toString(), isNot(contains('alex@example.com')));
+      expect(restored.uri.toString(), '/verification-sent');
+      router.goNamed(AppRoutes.login);
+      await tester.pumpAndSettle();
+      router.goNamed(AppRoutes.verificationSent);
+      await tester.pumpAndSettle();
+      expect(find.text('alex@example.com'), findsNothing);
+      expect(find.byKey(const ValueKey('verification-idle')), findsOneWidget);
+    },
+  );
+}