fixed guardian login edge cases and misleading placeholders on failed loads

lib/view/login/guardian_login_controller.dart

@@ -54,9 +54,14 @@ class GuardianLoginController extends ChangeNotifier {
   String? get errorMessage => _errorMessage;
   String? get errorDetails => _errorDetails;
 
-  bool canResend() {
+  bool canResend() => resendCooldown() == Duration.zero;
+
+  /// Restzeit, bis [resend] wieder erlaubt ist.
+  Duration resendCooldown() {
     final pending = _pending;
-    return pending != null && !_now().isBefore(pending.resendAvailableAt);
+    if (pending == null) return Duration.zero;
+    final remaining = pending.resendAvailableAt.difference(_now());
+    return remaining.isNegative ? Duration.zero : remaining;
   }
 
   /// Picks up a request started before the app was closed.
@@ -77,8 +82,12 @@ class GuardianLoginController extends ChangeNotifier {
   Future<bool> requestCode(String email) async {
     final normalized = email.trim().toLowerCase();
     if (DemoMode.matchesGuardian(normalized)) {
-      await _signIn(GuardianSession(email: normalized, isDemo: true));
-      return true;
+      var signedIn = false;
+      await _run(() async {
+        await _signIn(GuardianSession(email: normalized, isDemo: true));
+        signedIn = true;
+      });
+      return signedIn;
     }
     await _run(() async {
       final secret = DeviceBinding.generateSecret();
@@ -128,6 +137,17 @@ class GuardianLoginController extends ChangeNotifier {
     return _complete(linkToken: link.linkToken);
   }
 
+  /// A mail link that does not belong to the server the app talks to (a live
+  /// link while the app points at beta). Without this the tap would do nothing
+  /// at all.
+  void rejectForeignLink() {
+    _errorMessage =
+        'Dieser Anmeldelink gehört zu einem anderen Server als dem, mit dem '
+        'die App gerade verbunden ist. Bitte gib den Code aus der E-Mail ein.';
+    _errorDetails = null;
+    notifyListeners();
+  }
+
   /// Abandons the running request, e.g. to correct a mistyped address.
   Future<void> changeEmail() async {
     await _store.clear();
@@ -140,7 +160,15 @@ class GuardianLoginController extends ChangeNotifier {
 
   Future<bool> _complete({String? code, String? linkToken}) async {
     final pending = _pending;
-    if (pending == null) return false;
+    if (pending == null) {
+      _errorMessage = GuardianLoginException.messageFor(
+        GuardianLoginError.requestExpired,
+      );
+      _errorDetails = null;
+      _step = GuardianLoginStep.enterEmail;
+      notifyListeners();
+      return false;
+    }
     var signedIn = false;
     await _run(() async {
       await _verify.run(
@@ -188,9 +216,16 @@ class GuardianLoginController extends ChangeNotifier {
   }
 
   static Future<void> _defaultSignIn(Session session) async {
-    // Drop any widget snapshot of a previous account before the new one loads.
-    await WidgetSync.clear();
-    await WidgetSync.triggerUpdate();
+    // Sign in first: the one-time code is already spent at this point, so a
+    // failing widget reset must not cost the session (the user would have to
+    // request a fresh mail for a login that actually succeeded).
     await SessionManager().signIn(session);
+    // Drop any widget snapshot of a previous account.
+    try {
+      await WidgetSync.clear();
+      await WidgetSync.triggerUpdate();
+    } on Object catch (e) {
+      log('Guardian login: widget reset failed: $e');
+    }
   }
 }

lib/view/login/login.dart

@@ -7,6 +7,7 @@ import '../../api/marianumconnect/marianumconnect_endpoint.dart' as mc;
 import '../../auth_link/guardian_link_listener.dart';
 import '../../auth_link/guardian_login_link.dart';
 import '../../background/widget_background_task.dart';
+import '../../session/session_lifecycle.dart';
 import '../../state/app/modules/account/bloc/account_bloc.dart';
 import '../../state/app/modules/account/bloc/account_state.dart';
 import '../../state/app/modules/settings/bloc/settings_cubit.dart';
@@ -14,6 +15,7 @@ import '../../storage/dev_tools_settings.dart';
 import '../../storage/settings.dart' as model;
 import '../../theming/light_app_theme.dart';
 import '../../utils/haptics.dart';
+import '../../widget/info_dialog.dart';
 import '../pages/settings/widgets/endpoint_picker.dart';
 import 'guardian_login_controller.dart';
 import 'login_controller.dart';
@@ -54,6 +56,16 @@ class _LoginState extends State<Login> with SingleTickerProviderStateMixin {
     });
     GuardianLinkListener.pending.addListener(_consumeGuardianLink);
     _consumeGuardianLink();
+    WidgetsBinding.instance.addPostFrameCallback((_) => _showSignOutNotice());
+  }
+
+  /// An involuntary sign-out (expired token, rotated password) otherwise just
+  /// drops the user here without a word.
+  void _showSignOutNotice() {
+    final notice = SessionLifecycle.signOutNotice.value;
+    if (notice == null || !mounted) return;
+    SessionLifecycle.signOutNotice.value = null;
+    InfoDialog.show(context, notice, title: 'Erneut anmelden');
   }
 
   /// A tapped mail link finishes the guardian login without typing the code.
@@ -65,10 +77,13 @@ class _LoginState extends State<Login> with SingleTickerProviderStateMixin {
       uri,
       apiBase: Uri.parse(mc.MarianumConnectEndpoint.current()),
     );
-    if (link == null) return;
     await _guardianRestored;
     if (!mounted) return;
     setState(() => _audience = LoginAudience.guardian);
+    if (link == null) {
+      _guardianController.rejectForeignLink();
+      return;
+    }
     final signedIn = await _guardianController.submitLink(link);
     if (signedIn && mounted) _onLoginSuccess();
   }

lib/view/login/widgets/guardian_login_card.dart

@@ -158,7 +158,7 @@ class _GuardianLoginCardState extends State<GuardianLoginCard> {
   Widget _buildCodeStep(BuildContext context) {
     final theme = Theme.of(context);
     final pending = _controller.pending!;
-    final remaining = pending.resendAvailableAt.difference(DateTime.now());
+    final remaining = _controller.resendCooldown();
     return Form(
       key: _codeFormKey,
       child: LoginCardFrame(

lib/view/login/widgets/login_audience_card.dart

@@ -14,7 +14,7 @@ class LoginAudienceCard extends StatelessWidget {
   @override
   Widget build(BuildContext context) => LoginCardFrame(
     title: 'Anmelden',
-    hint: 'Bite wähle deine Anmeldemethode',
+    hint: 'Bitte wähle deine Anmeldemethode',
     children: [
       _AudienceButton(
         key: const Key('login-audience-school'),