diff --git a/lib/pages/backup_page.dart b/lib/pages/backup_page.dart
index 21ecad4..b490e9b 100644
--- a/lib/pages/backup_page.dart
+++ b/lib/pages/backup_page.dart
@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:typed_data';
 
 import 'package:file_picker/file_picker.dart';
@@ -26,9 +27,18 @@ class BackupPage extends StatefulWidget {
 
 class _BackupPageState extends State<BackupPage> {
   late final ConfigArchive _archive = widget.runtime.backupArchive;
+  Completer<void>? _cancelled;
+  StreamIterator<Uint8List>? _importStream;
   bool _includeAccount = false;
   bool _busy = false;
   bool _waitingForReload = false;
+  bool get _operationActive {
+    AppLog.instance.trace(
+      "lib/pages/backup_page.dart::_BackupPageState._operationActive.get",
+    );
+    return mounted && _cancelled?.isCompleted == false;
+  }
+
   String? _message;
   String? get _statusMessage {
     AppLog.instance.trace(
@@ -39,6 +49,31 @@ class _BackupPageState extends State<BackupPage> {
         : _message;
   }
 
+  @override
+  void dispose() {
+    AppLog.instance.trace(
+      "lib/pages/backup_page.dart::_BackupPageState.dispose",
+    );
+    _cancelOperation();
+    super.dispose();
+  }
+
+  void _cancelOperation() {
+    AppLog.instance.trace(
+      "lib/pages/backup_page.dart::_BackupPageState._cancelOperation",
+    );
+    final cancelled = _cancelled;
+    if (cancelled != null && !cancelled.isCompleted) cancelled.complete();
+    // Provider cleanup errors cannot be shown after leaving the page.
+    unawaited(
+      _importStream?.cancel().catchError((_) {
+        AppLog.instance.trace(
+          "lib/pages/backup_page.dart::_BackupPageState._cancelOperation.closure#1",
+        );
+      }),
+    );
+  }
+
   Future<bool> _confirm(String title, Widget content, String action) {
     AppLog.instance.trace(
       "lib/pages/backup_page.dart::_BackupPageState._confirm",
@@ -59,6 +94,7 @@ class _BackupPageState extends State<BackupPage> {
       );
 
       if (_busy || !mounted) return;
+      final cancelled = _cancelled = Completer<void>();
       setState(() {
         AppLog.instance.trace(
           "lib/pages/backup_page.dart::_BackupPageState._run.closure#1.closure#1",
@@ -71,6 +107,7 @@ class _BackupPageState extends State<BackupPage> {
       try {
         await action();
       } catch (error, stack) {
+        if (cancelled.isCompleted) return;
         final expected =
             error is ConfigArchiveException ||
             error is FormatException ||
@@ -126,6 +163,8 @@ class _BackupPageState extends State<BackupPage> {
           };
         });
       } finally {
+        if (!cancelled.isCompleted) cancelled.complete();
+        _cancelled = null;
         if (mounted)
           setState(() {
             AppLog.instance.trace(
@@ -154,9 +193,12 @@ class _BackupPageState extends State<BackupPage> {
             '仍要导出',
           ))
         return;
-      if (!mounted) return;
-      final bytes = await _archive.export(includeAccount: includeAccount);
-      if (!mounted) return;
+      if (!_operationActive) return;
+      final bytes = await _archive.export(
+        includeAccount: includeAccount,
+        cancelled: _cancelled?.future,
+      );
+      if (!_operationActive) return;
       final date = DateTime.now().toIso8601String().substring(0, 10);
       final saved = await FilePicker.saveFile(
         fileName: 'XMPlus-$date${includeAccount ? '-含账号' : ''}.zip',
@@ -164,7 +206,7 @@ class _BackupPageState extends State<BackupPage> {
         mimeType: 'application/zip',
         dialogTitle: '保存备份',
       );
-      if (saved != null && mounted)
+      if (saved != null && _operationActive)
         setState(() {
           AppLog.instance.trace(
             "lib/pages/backup_page.dart::_BackupPageState._export.closure#1.closure#1",
@@ -188,21 +230,34 @@ class _BackupPageState extends State<BackupPage> {
         type: FileType.custom,
         allowedExtensions: ['zip'],
       );
-      if (file == null || !mounted) return;
+      if (file == null || !_operationActive) return;
       final length = await file.length();
+      if (!_operationActive) return;
       if (length != null && length > ConfigArchive.maxBytes) {
         throw const ConfigArchiveException('备份超过 64 MiB');
       }
       // A bounded stream also handles providers which do not report file length.
       final bytes = BytesBuilder(copy: false);
-      await for (final chunk in file.readAsByteStream()) {
-        if (bytes.length + chunk.length > ConfigArchive.maxBytes) {
-          throw const ConfigArchiveException('备份超过 64 MiB');
+      final stream = _importStream = StreamIterator(file.readAsByteStream());
+      try {
+        while (await stream.moveNext()) {
+          if (!_operationActive) return;
+          final chunk = stream.current;
+          if (bytes.length + chunk.length > ConfigArchive.maxBytes) {
+            throw const ConfigArchiveException('备份超过 64 MiB');
+          }
+          bytes.add(chunk);
         }
-        bytes.add(chunk);
+      } finally {
+        _importStream = null;
+        await stream.cancel();
       }
-      final draft = await _archive.inspect(bytes.takeBytes());
-      if (!mounted) return;
+      if (!_operationActive) return;
+      final draft = await _archive.inspect(
+        bytes.takeBytes(),
+        cancelled: _cancelled?.future,
+      );
+      if (!_operationActive) return;
       final replacements = <String, String>{};
       for (final oldRoot in draft.missingDirectories) {
         if (!await _confirm(
@@ -211,11 +266,11 @@ class _BackupPageState extends State<BackupPage> {
           '选择目录',
         ))
           return;
-        if (!mounted) return;
+        if (!_operationActive) return;
         final selected = await FilePicker.getDirectoryPath(
           dialogTitle: '选择新的下载目录',
         );
-        if (selected == null || !mounted) return;
+        if (selected == null || !_operationActive) return;
         replacements[oldRoot] = selected;
       }
       final accepted = await _confirm(
@@ -236,7 +291,7 @@ class _BackupPageState extends State<BackupPage> {
         ),
         '确认恢复',
       );
-      if (!accepted || !mounted) return;
+      if (!accepted || !_operationActive) return;
       try {
         await widget.runtime.restoreBackup(draft, relocatedRoots: replacements);
       } catch (_) {
@@ -266,14 +321,22 @@ class _BackupPageState extends State<BackupPage> {
   @override
   Widget build(BuildContext context) {
     AppLog.instance.trace("lib/pages/backup_page.dart::_BackupPageState.build");
-    return ListenableBuilder(
-      listenable: widget.runtime,
-      builder: (context, _) {
+    return PopScope(
+      onPopInvokedWithResult: (didPop, _) {
         AppLog.instance.trace(
           "lib/pages/backup_page.dart::_BackupPageState.build.closure#1",
         );
-        return _content(context);
+        if (didPop) _cancelOperation();
       },
+      child: ListenableBuilder(
+        listenable: widget.runtime,
+        builder: (context, _) {
+          AppLog.instance.trace(
+            "lib/pages/backup_page.dart::_BackupPageState.build.closure#2",
+          );
+          return _content(context);
+        },
+      ),
     );
   }
 
diff --git a/lib/pages/developer_settings_page.dart b/lib/pages/developer_settings_page.dart
index 1f7e308..fdfa7a4 100644
--- a/lib/pages/developer_settings_page.dart
+++ b/lib/pages/developer_settings_page.dart
@@ -30,6 +30,14 @@ class _DeveloperSettingsPageState extends State<DeveloperSettingsPage> {
   String? _selected;
   String? _error;
   bool _busy = false;
+  bool _leaving = false;
+
+  bool _canContinueExport() {
+    AppLog.instance.trace(
+      "lib/pages/developer_settings_page.dart::_DeveloperSettingsPageState._canContinueExport",
+    );
+    return mounted && !_leaving;
+  }
 
   @override
   void initState() {
@@ -202,7 +210,7 @@ class _DeveloperSettingsPageState extends State<DeveloperSettingsPage> {
         "lib/pages/developer_settings_page.dart::_DeveloperSettingsPageState._export.closure#1",
       );
 
-      if (_busy) return;
+      if (_busy || !_canContinueExport()) return;
       final session = _sessions.where((session) {
         AppLog.instance.trace(
           "lib/pages/developer_settings_page.dart::_DeveloperSettingsPageState._export.closure#1.closure#1",
@@ -221,19 +229,25 @@ class _DeveloperSettingsPageState extends State<DeveloperSettingsPage> {
       try {
         if (clipboard) {
           final snapshot = await _log.snapshot(session.fileName);
+          if (!_canContinueExport()) return;
           if (!snapshot.canCopyToClipboard(android: Platform.isAndroid)) {
             throw StateError('日志过大，无法完整复制，请导出到文件');
           }
           final text = await snapshot.readForClipboard(
             android: Platform.isAndroid,
           );
+          if (!_canContinueExport()) return;
           await Clipboard.setData(ClipboardData(text: text));
-          if (mounted) _message('日志已复制');
+          if (_canContinueExport()) _message('日志已复制');
         } else {
-          final destination = await exportLogSession(session);
-          if (destination != null && mounted) _message('日志已导出');
+          final destination = await exportLogSession(
+            session,
+            canStart: _canContinueExport,
+          );
+          if (destination != null && _canContinueExport()) _message('日志已导出');
         }
       } catch (error, stack) {
+        if (!_canContinueExport()) return;
         if (!_log.errorWasRecorded(error)) {
           _log.write(
             AppLogLevel.warning,
@@ -301,7 +315,7 @@ class _DeveloperSettingsPageState extends State<DeveloperSettingsPage> {
       "lib/pages/developer_settings_page.dart::_DeveloperSettingsPageState.build",
     );
 
-    return ListenableBuilder(
+    final content = ListenableBuilder(
       listenable: widget.runtime,
       builder: (context, _) {
         AppLog.instance.trace(
@@ -515,5 +529,14 @@ class _DeveloperSettingsPageState extends State<DeveloperSettingsPage> {
         );
       },
     );
+    return PopScope(
+      child: content,
+      onPopInvokedWithResult: (didPop, _) {
+        AppLog.instance.trace(
+          "lib/pages/developer_settings_page.dart::_DeveloperSettingsPageState.build.closure#2",
+        );
+        if (didPop) _leaving = true;
+      },
+    );
   }
 }
diff --git a/lib/services/log_export.dart b/lib/services/log_export.dart
index 27983ab..37a9fcc 100644
--- a/lib/services/log_export.dart
+++ b/lib/services/log_export.dart
@@ -8,16 +8,19 @@ import 'android_platform.dart';
 import 'app_log.dart';
 
 /// Exports only a session returned by the logger, never an arbitrary path.
-/// A null result means the user cancelled the platform save dialog.
-Future<Uri?> exportLogSession(LogSession session) {
+/// A null result means the caller or the platform save dialog cancelled.
+/// [canStart] gates preparation; an opened save dialog can still finish.
+Future<Uri?> exportLogSession(LogSession session, {bool Function()? canStart}) {
   AppLog.instance.trace("lib/services/log_export.dart::exportLogSession");
   return AppLog.instance.runWithErrorScope(() async {
     AppLog.instance.trace(
       "lib/services/log_export.dart::exportLogSession.closure#1",
     );
 
+    if (canStart?.call() == false) return null;
     final log = AppLog.instance;
     final sessions = await log.sessions();
+    if (canStart?.call() == false) return null;
     if (!sessions.any((candidate) {
       AppLog.instance.trace(
         "lib/services/log_export.dart::exportLogSession.closure#1.closure#1",
@@ -35,6 +38,7 @@ Future<Uri?> exportLogSession(LogSession session) {
       throw ArgumentError.value(name, 'fileName', '日志文件名无效');
     }
     final snapshot = await log.snapshot(name);
+    if (canStart?.call() == false) return null;
     if (Platform.isAndroid) {
       return AndroidPlatform.exportLogSnapshot(snapshot, name);
     }
diff --git a/lib/storage/config_archive.dart b/lib/storage/config_archive.dart
index c309189..80f11a7 100644
--- a/lib/storage/config_archive.dart
+++ b/lib/storage/config_archive.dart
@@ -1,6 +1,7 @@
 // ZIP layout adapted from PiliPlus lib/utils/config_archive.dart, commit
 // d9e9626f1a3f89cd9ca85e18f61aaba02634e12a (GNU GPL v3).
 // Source: https://github.com/bggRGjQaUbCoE/PiliPlus
+import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ -116,11 +117,33 @@ class ConfigArchive {
     return sha256.convert(utf8.encode(storage.directory)).toString();
   }
 
-  Future<List<int>> export({bool includeAccount = false}) async {
+  Future<List<int>> export({
+    bool includeAccount = false,
+    Future<void>? cancelled,
+  }) async {
     AppLog.instance.trace(
       "lib/storage/config_archive.dart::ConfigArchive.export",
     );
 
+    var stopped = false;
+    unawaited(
+      cancelled?.then((_) {
+        AppLog.instance.trace(
+          "lib/storage/config_archive.dart::ConfigArchive.export.closure#1",
+        );
+        stopped = true;
+      }),
+    );
+    void checkCancelled() {
+      AppLog.instance.trace(
+        "lib/storage/config_archive.dart::ConfigArchive.export.checkCancelled",
+      );
+      if (stopped) throw const ConfigArchiveException('备份导出已取消');
+    }
+
+    // Observe an already completed cancellation before preparing the archive.
+    await Future<void>.value();
+    checkCancelled();
     final state = storage.state;
     final tasks = {
       'downloads': _clean(state['downloads']),
@@ -137,11 +160,13 @@ class ConfigArchive {
     if (includeAccount) {
       final records = <Map<String, dynamic>>[];
       for (final entry in (state['accounts'] as Map).entries) {
+        checkCancelled();
         final record = entry.value as Map;
         Map<String, dynamic>? pair;
         final ref = record['credentialRef'];
         if (ref is String) {
           final encoded = await secrets.read(ref);
+          checkCancelled();
           if (encoded == null)
             throw const ConfigArchiveException('安全凭据缺失，未导出备份');
           final credentials = Credentials.parse(encoded);
@@ -162,6 +187,7 @@ class ConfigArchive {
         ...tasks,
       };
     }
+    checkCancelled();
     files['meta.json'] = {
       'type': 'data_archive',
       'formatVersion': 65536,
@@ -187,11 +213,36 @@ class ConfigArchive {
     return bytes;
   }
 
-  Future<ArchiveImport> inspect(List<int> bytes) async {
+  Future<ArchiveImport> inspect(
+    List<int> bytes, {
+    Future<void>? cancelled,
+  }) async {
     AppLog.instance.trace(
       "lib/storage/config_archive.dart::ConfigArchive.inspect",
     );
 
+    var stopped = false;
+    XmlyClient? checkingAccount;
+    unawaited(
+      cancelled?.then((_) {
+        AppLog.instance.trace(
+          "lib/storage/config_archive.dart::ConfigArchive.inspect.closure#1",
+        );
+        stopped = true;
+        // These clients belong to the preview, never to the active accounts.
+        checkingAccount?.close();
+      }),
+    );
+    void checkCancelled() {
+      AppLog.instance.trace(
+        "lib/storage/config_archive.dart::ConfigArchive.inspect.checkCancelled",
+      );
+      if (stopped) throw const ConfigArchiveException('备份导入已取消');
+    }
+
+    // Observe an already completed cancellation before parsing the ZIP.
+    await Future<void>.value();
+    checkCancelled();
     final Map<String, dynamic> payload;
     try {
       if (bytes.length > maxBytes || bytes.isEmpty)
@@ -247,15 +298,17 @@ class ConfigArchive {
     // No mutation, SMS, claim or report: candidate verification is config only.
     final account = payload['account.json'] as Map?;
     for (final record in account?['accounts'] as List? ?? const []) {
+      checkCancelled();
       if ((record as Map)['credentials'] == null) continue;
       final pair = Credentials.parse(record['credentials']);
-      final client = XmlyClient(credentials: pair);
+      final client = checkingAccount = XmlyClient(credentials: pair);
       try {
         final quota = await client.queryQuota();
         if (quota.remainingSeconds < 0)
           throw const ConfigArchiveException('备份账号无法核验');
       } finally {
         client.close();
+        checkingAccount = null;
       }
     }
     final missing = <String>{};
@@ -264,6 +317,7 @@ class ConfigArchive {
         "lib/storage/config_archive.dart::ConfigArchive.inspect.roots",
       );
 
+      checkCancelled();
       if (node is Map) {
         for (final entry in node.entries) {
           if (_rootKeys.contains(entry.key) &&
@@ -282,6 +336,7 @@ class ConfigArchive {
     }
 
     await roots(payload);
+    checkCancelled();
     final sameOrigin = payload['meta.json']['origin'] == _origin;
     final summary = <String>[
       if (payload.containsKey('setting.json')) '替换应用设置',