fixed guardian login edge cases and misleading placeholders on failed loads

lib/view/pages/timetable/timetable.dart

@@ -12,7 +12,6 @@ import '../../../state/app/modules/timetable/bloc/timetable_state.dart';
 import '../../../state/app/modules/timetable/policy/timetable_policy.dart';
 import '../../../state/app/modules/timetable/subject/timetable_subject.dart';
 import '../../../utils/haptics.dart';
-import '../../../widget/app_progress_indicator.dart';
 import '../../../widget/child_switcher.dart';
 import '../../../widget/demo_restricted.dart';
 import 'custom_events/custom_event_edit_dialog.dart';
@@ -29,6 +28,11 @@ class Timetable extends StatefulWidget {
 }
 
 class _TimetableState extends State<Timetable> {
+  /// One calendar key per subject: a new subject (child switch, foreign plan)
+  /// must not inherit the displayed week of the previous one, but coming back
+  /// to a subject should find its calendar where it was left.
+  final Map<TimetableSubject, GlobalKey<TimetableCalendarViewState>>
+  _calendarKeys = {};
   GlobalKey<TimetableCalendarViewState> _calendarKey =
       GlobalKey<TimetableCalendarViewState>();
   TimetableSubject? _calendarSubject;
@@ -107,7 +111,10 @@ class _TimetableState extends State<Timetable> {
     // previous calendar state.
     if (subject != _calendarSubject) {
       _calendarSubject = subject;
-      _calendarKey = GlobalKey<TimetableCalendarViewState>();
+      _calendarKey = _calendarKeys.putIfAbsent(
+        subject,
+        GlobalKey<TimetableCalendarViewState>.new,
+      );
     }
     final innerState = context.watch<B>().state.data;
     final atToday = innerState != null && _isOnInitialWeek(innerState);
@@ -204,20 +211,16 @@ class _TimetableState extends State<Timetable> {
 }
 
 /// Shown instead of a plan when the session has none, i.e. a guardian whose
-/// children are not known (yet).
+/// children are not known (yet). [NoChildrenPlaceholder] tells a pending or
+/// failed capability load apart from a confirmed empty list.
 class _NoTimetableView extends StatelessWidget {
   const _NoTimetableView();
 
   @override
-  Widget build(BuildContext context) {
-    final capabilities = context.watch<CapabilitiesCubit>().state;
-    return Scaffold(
-      appBar: AppBar(title: const Text('Stunden & Vertretungsplan')),
-      body: capabilities.loaded
-          ? const NoChildrenPlaceholder()
-          : const Center(child: AppProgressIndicator.large()),
-    );
-  }
+  Widget build(BuildContext context) => Scaffold(
+    appBar: AppBar(title: const Text('Stunden & Vertretungsplan')),
+    body: const NoChildrenPlaceholder(),
+  );
 }
 
 /// Slim banner shown at the top of the timetable while a foreign element's plan