fix: preserve queued settings and recover interrupted or corrupt state

mobile/test/widgets/settings_test.dart

@@ -9,9 +9,61 @@ import 'package:hepan_everyday/services/calendar_service.dart';
 import '../support/fakes.dart';
 
 import 'navigation_test.dart' show uiController;
+import '../services/calendar_service_test.dart' show CalendarProvider;
+import '../domain/schedule_engine_test.dart' show course;
+
+import 'package:hepan_everyday/services/android_calendar_service.dart';
+import 'package:hepan_everyday/domain/app_snapshot.dart';
+import 'package:hepan_everyday/domain/app_settings.dart';
+import 'package:hepan_everyday/domain/semester.dart';
 
 void main() {
   setUpAll(tzdata.initializeTimeZones);
+  testWidgets(
+    'partial initial calendar sync exposes working cleanup action while switch is off',
+    (tester) async {
+      final provider = CalendarProvider()..failAfterFirst = true;
+      final controller = AppController(
+        MemoryStore(
+          AppSnapshot(
+            courses: [
+              course(id: 'a'),
+              course(id: 'b'),
+            ],
+            settings: AppSettings(
+              semester: Semester(
+                startDate: DateTime(2026, 9, 9),
+                totalWeeks: 1,
+              ),
+            ),
+          ),
+        ),
+        FakeNotifications(),
+        AndroidCalendarService(provider),
+        DateTime.now,
+      );
+      await controller.initialize();
+      await controller.enableCalendarFromUserAction('local');
+      expect(controller.snapshot.settings.calendarEnabled, isFalse);
+      expect(provider.records, hasLength(1));
+      await tester.pumpWidget(
+        MaterialApp(home: SettingsPage(controller: controller)),
+      );
+      await tester.pumpAndSettle();
+      await tester.scrollUntilVisible(
+        find.text('重试清理课程日程'),
+        250,
+        scrollable: find.byType(Scrollable).first,
+      );
+      await tester.ensureVisible(find.text('重试清理课程日程'));
+      await tester.pumpAndSettle();
+      await tester.tap(find.text('重试清理课程日程'));
+      await tester.pumpAndSettle();
+      expect(provider.records, isEmpty);
+      expect(controller.snapshot.calendarCleanupPending, isFalse);
+      controller.dispose();
+    },
+  );
   testWidgets('calendar provider failure is explained and keeps switch off', (
     tester,
   ) async {