fix: preserve queued settings and recover interrupted or corrupt state

mobile/lib/app/app_controller.dart

@@ -85,7 +85,10 @@ class AppController extends ChangeNotifier {
   Future<void> leaveDemo() => _run(() async {
     isDemo = false;
   });
-  Future<void> updateSettings(AppSettings value) => _run(() async {
+  Future<void> updateSettings(
+    AppSettings Function(AppSettings current) change,
+  ) => _run(() async {
+    final value = change(snapshot.settings);
     if (![5, 10, 15, 30, 60].contains(value.reminderMinutes)) {
       throw ArgumentError('提醒时间无效');
     }
@@ -170,43 +173,54 @@ class AppController extends ChangeNotifier {
     }
     calendarSyncError = null;
   });
-  Future<void> enableCalendarFromUserAction(
-    String calendarId,
-  ) => _run(() async {
-    if (isDemo) throw StateError('示例课表不会导入日历');
-    if (snapshot.settings.semester == null) throw StateError('请先设置学期');
-    if (!await calendar.requestAccess()) {
-      calendarSyncError = '日历权限未获允许';
-      return;
-    }
-    if (snapshot.calendarCleanupPending) {
-      await _cleanupCalendar();
-    }
-    final calendars = await calendar.listWritableCalendars();
-    if (!calendars.any((c) => c.id == calendarId)) {
-      calendarSyncError = '请选择可写入的日历';
-      return;
-    }
-    final settings = snapshot.settings.copyWith(
-      calendarEnabled: true,
-      calendarId: calendarId,
-    );
-    // Keep the chosen calendar for recovery if the first native sync fails midway.
-    await _save(
-      snapshot.copyWith(settings: settings.copyWith(calendarEnabled: false)),
-    );
-    try {
-      final ids = await calendar.sync(
-        ScheduleEngine.occurrences(snapshot.courses, settings.semester!),
-        calendarId,
-        snapshot.calendarEventIds,
-      );
-      await _save(snapshot.copyWith(settings: settings, calendarEventIds: ids));
-      calendarSyncError = null;
-    } catch (_) {
-      calendarSyncError = '日历同步失败，可重试';
-    }
-  });
+  Future<void> enableCalendarFromUserAction(String calendarId) =>
+      _run(() async {
+        if (isDemo) throw StateError('示例课表不会导入日历');
+        if (snapshot.settings.semester == null) throw StateError('请先设置学期');
+        if (!await calendar.requestAccess()) {
+          calendarSyncError = '日历权限未获允许';
+          return;
+        }
+        if (snapshot.calendarCleanupPending) {
+          await _cleanupCalendar();
+        }
+        final calendars = await calendar.listWritableCalendars();
+        if (!calendars.any((c) => c.id == calendarId)) {
+          calendarSyncError = '请选择可写入的日历';
+          return;
+        }
+        final settings = snapshot.settings.copyWith(
+          calendarEnabled: true,
+          calendarId: calendarId,
+        );
+        // Keep the chosen calendar for recovery if the first native sync fails midway.
+        await _save(
+          snapshot.copyWith(
+            settings: settings.copyWith(calendarEnabled: false),
+            calendarCleanupPending: true,
+            calendarEventIds: snapshot.settings.calendarId == calendarId
+                ? snapshot.calendarEventIds
+                : {},
+          ),
+        );
+        try {
+          final ids = await calendar.sync(
+            ScheduleEngine.occurrences(snapshot.courses, settings.semester!),
+            calendarId,
+            snapshot.calendarEventIds,
+          );
+          await _save(
+            snapshot.copyWith(
+              settings: settings,
+              calendarEventIds: ids,
+              calendarCleanupPending: false,
+            ),
+          );
+          calendarSyncError = null;
+        } catch (_) {
+          calendarSyncError = '日历同步失败，可重试';
+        }
+      });
   Future<void> enableRemindersFromUserAction() => _run(() async {
     if (isDemo) throw StateError('示例课表不会生成提醒');
     await notifications.requestPermissions();
@@ -218,6 +232,16 @@ class AppController extends ChangeNotifier {
     await _reconcile();
   });
   Future<void> refreshServices() => _run(_reconcile);
+  Future<void> startFreshData() => _run(() async {
+    if (storageReady) {
+      throw StateError('保存文件正常，无需重新建立');
+    }
+    snapshot = await store.startFresh();
+    storageReady = true;
+    isDemo = false;
+    lastError = null;
+    await _reconcile();
+  });
   Future<void> retryCalendarCleanup() => _run(() async {
     if (await calendar.requestAccess()) {
       await _cleanupCalendar();