fixed guardian login edge cases and misleading placeholders on failed loads

lib/session/session_lifecycle.dart

@@ -1,16 +1,24 @@
 import 'dart:developer';
 
+import 'package:flutter/foundation.dart';
+
 import '../api/marianumconnect/queries/auth_logout/auth_logout.dart';
 import '../auth_link/guardian_link_listener.dart';
 import '../push/push_registration.dart';
 import 'session_manager.dart';
 
 abstract final class SessionLifecycle {
+  /// Why the last sign-out happened, when the user did not ask for it. The
+  /// login screen shows it once and clears it — without it an expired session
+  /// just drops the user on the login screen with no explanation.
+  static final ValueNotifier<String?> signOutNotice = ValueNotifier(null);
+
   /// Ordered teardown: unregister push and revoke the Nextcloud app passwords
   /// (while those credentials still exist), then revoke the MC bearer token,
   /// finally wipe the local session. Each step is best-effort so an offline
   /// sign-out still reaches a clean local state.
-  static Future<void> signOut() async {
+  static Future<void> signOut({String? notice}) async {
+    signOutNotice.value = notice;
     try {
       await PushRegistration().logoutCleanup();
     } on Object catch (e) {