Show accepted signup delivery without a second send step (#62)

frontend/app/test/routing_test.dart

@@ -42,6 +42,44 @@ Future<GoRouter> openRoute(
 }
 
 void main() {
+  testWidgets('queued signup receipt is transient and updates its recipient', (
+    tester,
+  ) async {
+    final router = await openRoute(tester, '/');
+    await tester.pumpAndSettle();
+    router.goNamed(
+      AppRoutes.verificationSent,
+      extra: const VerificationDelivery(
+        email: 'first@example.com',
+        isSimulated: false,
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(find.byKey(const ValueKey('verification-sent')), findsOneWidget);
+    expect(find.text('first@example.com'), findsOneWidget);
+    router.goNamed(
+      AppRoutes.verificationSent,
+      extra: const VerificationDelivery(
+        email: 'second@example.com',
+        isSimulated: false,
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(find.text('first@example.com'), findsNothing);
+    expect(find.text('second@example.com'), findsOneWidget);
+    final restored = router.routeInformationParser.restoreRouteInformation(
+      router.routerDelegate.currentConfiguration,
+    )!;
+    expect(restored.state.toString(), isNot(contains('second@example.com')));
+    expect(restored.uri.toString(), '/verification-sent');
+    router.goNamed(AppRoutes.login);
+    await tester.pumpAndSettle();
+    router.goNamed(AppRoutes.verificationSent);
+    await tester.pumpAndSettle();
+    expect(find.byKey(const ValueKey('verification-idle')), findsOneWidget);
+    expect(find.text('second@example.com'), findsNothing);
+  });
+
   for (final language in ['en', 'ru']) {
     testWidgets(
       'verified link keeps success visible and prefills login ($language)',