added support for multiple accounts with an account switcher in settings

lib/api/marianumconnect/auth/auth_interceptor.dart

@@ -19,6 +19,15 @@ class MarianumConnectAuthInterceptor extends Interceptor {
   // each spawning a fresh row in api_tokens.
   Future<bool>? _pendingReLogin;
 
+  static Future<bool>? _anyPendingReLogin;
+
+  /// Resolves once no silent re-login is running. An account switch waits for
+  /// it — the renewed token would otherwise land in the next account's slot.
+  static Future<void> idle() async {
+    final pending = _anyPendingReLogin;
+    if (pending != null) await pending;
+  }
+
   MarianumConnectAuthInterceptor({
     MarianumConnectTokenStorage tokenStorage =
         const MarianumConnectTokenStorage(),
@@ -81,8 +90,10 @@ class MarianumConnectAuthInterceptor extends Interceptor {
     if (inFlight != null) return inFlight;
     final fresh = _performReLogin();
     _pendingReLogin = fresh;
+    _anyPendingReLogin = fresh;
     fresh.whenComplete(() {
       if (identical(_pendingReLogin, fresh)) _pendingReLogin = null;
+      if (identical(_anyPendingReLogin, fresh)) _anyPendingReLogin = null;
     });
     return fresh;
   }

lib/api/marianumconnect/auth/session_validator.dart

@@ -8,9 +8,10 @@ import '../queries/auth_verify/auth_verify.dart';
 
 /// Credential probe. A server-side password rotation forces a re-login on the
 /// next cold start even when the bearer token would still be accepted.
+/// Another stored account then takes over.
 class SessionValidator {
   static Future<void> probeStored({
-    required Future<void> Function() onInvalidated,
+    required Future<void> Function(String? nextAccountId) onInvalidated,
   }) async {
     final session = SessionManager().current;
     // The probes use their own dio (bypassing the demo interceptor), so a demo
@@ -24,18 +25,18 @@ class SessionValidator {
       }
     } on AuthException catch (e) {
       if (e.statusCode != 401) return;
-      // The probed account already signed out; the 401 must not sign out
-      // whoever logged in meanwhile.
+      // The probed account is no longer the active one; the 401 must not
+      // sign out whoever took over meanwhile.
       if (!SessionManager().isCurrentSession(epoch)) return;
       log('MC: stored session rejected — forcing re-login');
-      await SessionLifecycle.signOut(
+      final next = await SessionLifecycle.signOut(
         notice: switch (session) {
           CredentialSession() =>
             'Deine Zugangsdaten wurden vom Server abgelehnt. Vermutlich '
                 'wurde dein Passwort geändert. Bitte melde dich erneut an.',
         },
       );
-      await onInvalidated();
+      await onInvalidated(next);
     } catch (e) {
       log('MC: background session check failed (transient): $e');
     }

lib/api/marianumconnect/auth/token_storage.dart

@@ -60,6 +60,26 @@ class MarianumConnectTokenStorage {
     );
   }
 
+  static const bearerKey = _tokenKey;
+  static const fieldKeys = [_tokenKey, _tokenIdKey, _expiresAtKey];
+
+  /// Raw stored fields, for parking the token of an inactive account.
+  Future<Map<String, String>> readAll() async => {
+    for (final key in fieldKeys) key: ?await _storage.read(key: key),
+  };
+
+  /// Restores fields from [readAll]; missing ones are deleted.
+  Future<void> writeAll(Map<String, String> fields) async {
+    for (final key in fieldKeys) {
+      final value = fields[key];
+      if (value == null) {
+        await _storage.delete(key: key);
+      } else {
+        await _storage.write(key: key, value: value);
+      }
+    }
+  }
+
   Future<void> clear() async {
     await _storage.delete(key: _tokenKey);
     await _storage.delete(key: _tokenIdKey);