diff --git a/ui/flutter/lib/core/window/window_capability_transport.dart b/ui/flutter/lib/core/window/window_capability_transport.dart
index 45506801..3fa2c6fc 100644
--- a/ui/flutter/lib/core/window/window_capability_transport.dart
+++ b/ui/flutter/lib/core/window/window_capability_transport.dart
@@ -52,6 +52,7 @@ class AppWindowCapabilityHost {
   CapabilityRegistry? _registry;
   AppWindowAppearance _appearance = const AppWindowAppearance.defaults();
   final Map<String, WindowController> _subscribers = {};
+  StreamSubscription<void>? _windowsChanged;
 
   bool get started => _registry != null;
 
@@ -59,14 +60,33 @@ class AppWindowCapabilityHost {
     if (_registry != null) return;
     _registry = registry;
     await _hostChannel.setMethodCallHandler(_handleCall);
+    _windowsChanged = onWindowsChanged.listen((_) => unawaited(_removeClosedSubscribers()));
   }
 
   Future<void> stop() async {
     _registry = null;
+    await _windowsChanged?.cancel();
+    _windowsChanged = null;
     _subscribers.clear();
     await _hostChannel.setMethodCallHandler(null);
   }
 
+  Future<void> _removeClosedSubscribers() async {
+    // Engine shutdown does not run Widget.dispose, so a closed child cannot
+    // always send window.unsubscribe itself.
+    final registry = _registry;
+    final candidates = _subscribers.keys.toSet();
+    if (registry == null || candidates.isEmpty) return;
+    try {
+      final windows = await WindowController.getAll();
+      if (!identical(registry, _registry)) return;
+      final openIds = windows.map((window) => window.windowId).toSet();
+      _subscribers.removeWhere((id, _) => candidates.contains(id) && !openIds.contains(id));
+    } catch (_) {
+      // The native window registry can already be gone during app shutdown.
+    }
+  }
+
   void updateAppearance(AppWindowAppearance appearance) {
     if (_appearance == appearance) return;
     _appearance = appearance;
diff --git a/ui/flutter/macos/Runner/MainFlutterWindow.swift b/ui/flutter/macos/Runner/MainFlutterWindow.swift
index 718f4c04..f4354059 100644
--- a/ui/flutter/macos/Runner/MainFlutterWindow.swift
+++ b/ui/flutter/macos/Runner/MainFlutterWindow.swift
@@ -4,6 +4,8 @@ import desktop_multi_window
 import window_manager
 
 class MainFlutterWindow: NSWindow {
+  private var childWindowCloseObservers: [ObjectIdentifier: NSObjectProtocol] = [:]
+
   override func awakeFromNib() {
     let flutterViewController = FlutterViewController()
     let windowFrame = self.frame
@@ -11,13 +13,45 @@ class MainFlutterWindow: NSWindow {
     self.setFrame(windowFrame, display: true)
 
     RegisterGeneratedPlugins(registry: flutterViewController)
-    FlutterMultiWindowPlugin.setOnWindowCreatedCallback { controller in
+    FlutterMultiWindowPlugin.setOnWindowCreatedCallback { [weak self] controller in
       RegisterGeneratedPlugins(registry: controller)
+      self?.releaseChildEngineOnClose(controller)
     }
 
     super.awakeFromNib()
   }
 
+  // desktop_multi_window removes closed windows from its registry, but plugin
+  // channels can still retain the window/controller/engine cycle. NSWindow.close
+  // alone therefore leaves each child Dart isolate and its heap running.
+  private func releaseChildEngineOnClose(_ controller: FlutterViewController) {
+    guard let window = controller.view.window else { return }
+    let key = ObjectIdentifier(window)
+    childWindowCloseObservers[key] = NotificationCenter.default.addObserver(
+      forName: NSWindow.willCloseNotification, object: window, queue: .main
+    ) { [weak self, weak controller, weak window] _ in
+      if let observer = self?.childWindowCloseObservers.removeValue(forKey: key) {
+        NotificationCenter.default.removeObserver(observer)
+      }
+      // Let close notifications and the plugin's registry removal finish before
+      // tearing down the engine that delivered the close request.
+      DispatchQueue.main.async { [weak controller, weak window] in
+        // window_manager's onEvent closure retains its plugin, which retains
+        // the manager and NSWindow even after the engine has stopped.
+        (window?.delegate as? WindowManager)?.onEvent = nil
+        window?.delegate = nil
+        controller?.engine.shutDownEngine()
+        window?.contentViewController = nil
+      }
+    }
+  }
+
+  deinit {
+    for observer in childWindowCloseObservers.values {
+      NotificationCenter.default.removeObserver(observer)
+    }
+  }
+
   override public func order(_ place: NSWindow.OrderingMode, relativeTo otherWin: Int) {
     super.order(place, relativeTo: otherWin)
     hiddenWindowAtLaunch()
diff --git a/ui/flutter/test/core/window/window_capability_lifecycle_test.dart b/ui/flutter/test/core/window/window_capability_lifecycle_test.dart
new file mode 100644
index 00000000..d50e0a97
--- /dev/null
+++ b/ui/flutter/test/core/window/window_capability_lifecycle_test.dart
@@ -0,0 +1,65 @@
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:gopeed/core/capabilities/app_capabilities.dart';
+import 'package:gopeed/core/capabilities/capability_rpc.dart';
+import 'package:gopeed/core/window/app_window_appearance.dart';
+import 'package:gopeed/core/window/window_capability_transport.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  const windows = MethodChannel('mixin.one/desktop_multi_window');
+  const channels = MethodChannel('mixin.one/desktop_multi_window/channels');
+  const codec = StandardMethodCodec();
+  final messenger = TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger;
+
+  tearDown(() async {
+    await AppWindowCapabilityHost.instance.stop();
+    messenger.setMockMethodCallHandler(windows, null);
+    messenger.setMockMethodCallHandler(channels, null);
+  });
+
+  testWidgets('closed engines lose appearance subscriptions without a Dart unsubscribe', (tester) async {
+    final deliveries = <String>[];
+    messenger.setMockMethodCallHandler(channels, (call) async {
+      if (call.method == 'invokeMethod') {
+        final args = Map<String, dynamic>.from(call.arguments as Map);
+        if (args['method'] == AppWindowRpcProtocol.event) deliveries.add(args['channel'] as String);
+      }
+      return null;
+    });
+    messenger.setMockMethodCallHandler(windows, (call) async {
+      if (call.method == 'getAllWindows') {
+        return [
+          {'windowId': 'live-child', 'windowArgument': ''},
+        ];
+      }
+      return null;
+    });
+    final host = AppWindowCapabilityHost.instance;
+    await host.start(CapabilityRegistry(createAppCapabilityCodecs()));
+    for (final id in ['closed-child', 'live-child']) {
+      await messenger.handlePlatformMessage(
+        channels.name,
+        codec.encodeMethodCall(
+          MethodCall('methodCall', {
+            'channel': AppWindowRpcProtocol.channelName,
+            'method': AppWindowRpcProtocol.subscribe,
+            'arguments': {'windowId': id},
+          }),
+        ),
+        (_) {},
+      );
+    }
+    await tester.pump();
+    deliveries.clear();
+    await messenger.handlePlatformMessage(
+      windows.name,
+      codec.encodeMethodCall(const MethodCall('onWindowsChanged')),
+      (_) {},
+    );
+    await tester.pump();
+    host.updateAppearance(const AppWindowAppearance(themeMode: 'dark', themeColor: 'green', locale: 'zh'));
+    await tester.pump();
+    expect(deliveries, ['mixin.one/window_controller/live-child']);
+  });
+}