fix: preserve queued settings and recover interrupted or corrupt state

mobile/test/app/app_controller_test.dart

@@ -38,6 +38,60 @@ void main() {
     );
   });
   tearDown(() => controller.dispose());
+  test(
+    'queued changes to different settings preserve disabling reminders',
+    () async {
+      await controller.initialize();
+
+      await Future.wait([
+        controller.updateSettings(
+          (current) => current.copyWith(remindersEnabled: false),
+        ),
+        controller.updateSettings(
+          (current) => current.copyWith(colorMode: ColorMode.single),
+        ),
+      ]);
+      expect(store.value!.settings.remindersEnabled, isFalse);
+      expect(store.value!.settings.colorMode, ColorMode.single);
+    },
+  );
+  test('partial first calendar sync survives restart and is cleaned before another destination', () async {
+    store.value = store.value!.copyWith(
+      courses: [
+        course(id: 'a'),
+        course(id: 'b'),
+      ],
+    );
+    final provider = CalendarProvider()..failAfterFirst = true;
+    final first = AppController(
+      store,
+      notifications,
+      AndroidCalendarService(provider),
+      controller.clock,
+    );
+    await first.initialize();
+    await first.enableCalendarFromUserAction('local');
+    expect(provider.records, hasLength(1));
+    first.dispose();
+    provider.failAfterFirst = false;
+    final reopened = AppController(
+      store,
+      notifications,
+      AndroidCalendarService(provider),
+      controller.clock,
+    );
+    await reopened.initialize();
+    expect(provider.records, isEmpty);
+    await reopened.enableCalendarFromUserAction('other');
+    expect(
+      provider.records.values.every((e) => e.calendarId == 'other'),
+      isTrue,
+    );
+    expect(provider.records, hasLength(2));
+    await reopened.disableCalendar(deleteEvents: true);
+    expect(provider.records, isEmpty);
+    reopened.dispose();
+  });
   test('turning off after interrupted first sync cleans events even without saved IDs', () async {
     store.value = store.value!.copyWith(
       courses: [
@@ -122,7 +176,7 @@ void main() {
     await controller.initialize();
     store.failSave = true;
     await controller.updateSettings(
-      controller.snapshot.settings.copyWith(reminderMinutes: 30),
+      (current) => current.copyWith(reminderMinutes: 30),
     );
     expect(controller.lastError, isNotNull);
     await controller.showDemo();
@@ -148,7 +202,7 @@ void main() {
     await controller.initialize();
     store.failSave = true;
     await controller.updateSettings(
-      controller.snapshot.settings.copyWith(reminderMinutes: 30),
+      (current) => current.copyWith(reminderMinutes: 30),
     );
     expect(controller.snapshot.settings.reminderMinutes, 15);
     expect(controller.lastError, isNotNull);
@@ -157,10 +211,10 @@ void main() {
     await controller.initialize();
     await Future.wait([
       controller.updateSettings(
-        controller.snapshot.settings.copyWith(reminderMinutes: 30),
+        (current) => current.copyWith(reminderMinutes: 30),
       ),
       controller.updateSettings(
-        controller.snapshot.settings.copyWith(reminderMinutes: 60),
+        (current) => current.copyWith(reminderMinutes: 60),
       ),
     ]);
     expect(store.value!.settings.reminderMinutes, 60);