window: extract XWindow primitive; XNotifications stops carrying focus

The window-focus signal had no business living on the notifications
primitive — it was there because the same NotificationsPlugin happened
to observe NSApplication active/resign for its own reasons. Splitting
it into a sibling XWindow primitive (with its own WindowPlugin on
macOS, ux/window/events) lets future consumers — paused video,
deferred-work scheduling, dock badge counts — read focus state without
pulling in UNUserNotificationCenter.

XNotifications now only exposes notification I/O (show/cancel + tap +
authorization). The 'type:focus' event-channel branch is gone.

lib/src/notifications/x_notifications.dart

@@ -8,20 +8,16 @@ import '../log.dart' show Log;
 
 final _log = Log.tag('notifications');
 
-/// Generic OS-notification + window-focus surface. Domain-agnostic — the
-/// caller decides when to emit and how to format the payload. Implemented
-/// on macOS via `UNUserNotificationCenter` and NSWindow key-focus
-/// observers (see `macos/Classes/NotificationsPlugin.swift`).
+/// OS-notification primitive. Domain-agnostic — the caller decides when
+/// to emit and how to format the payload. Implemented on macOS via
+/// `UNUserNotificationCenter` (see `macos/Classes/NotificationsPlugin.swift`).
+/// Window-focus state lives in [XWindow], not here.
 abstract interface class XNotifications {
   /// Production singleton — talks to the native plugin via MethodChannel
   /// + EventChannel. Tests inject a fake `XNotifications` directly into
   /// their service-under-test rather than swap this field.
   static final XNotifications instance = MethodChannelXNotifications();
 
-  /// True when the host window currently holds key focus. Defaults to
-  /// `true` until the native side emits an initial focus event.
-  ValueListenable<bool> get windowFocused;
-
   /// `null` = OS hasn't been asked; `true`/`false` after the user has
   /// answered an authorization prompt.
   ValueListenable<bool?> get authorized;
@@ -50,9 +46,6 @@ class MethodChannelXNotifications implements XNotifications {
   static const _channel = MethodChannel('ux/notifications');
   static const _eventsChannel = EventChannel('ux/notifications/events');
 
-  @override
-  final ValueEmitter<bool> windowFocused = ValueEmitter(true);
-
   @override
   final ValueEmitter<bool?> authorized = ValueEmitter(null);
 
@@ -121,9 +114,6 @@ class MethodChannelXNotifications implements XNotifications {
     if (event is! Map) return;
     final m = event.cast<Object?, Object?>();
     switch (m['type']) {
-      case 'focus':
-        final f = m['focused'];
-        if (f is bool) windowFocused.value = f;
       case 'authorization':
         final g = m['granted'];
         if (g is bool) authorized.value = g;

lib/src/window/x_window.dart

@@ -0,0 +1,49 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart' show ValueListenable;
+import 'package:flutter/services.dart';
+
+import '../core/emitter.dart';
+import '../log.dart' show Log;
+
+final _log = Log.tag('window');
+
+/// Host-window state primitive. Today exposes only [focused] (the macOS
+/// `NSApp.didBecomeActive` / `didResignActive` signal); future window-level
+/// state — minimized, occluded, screen — can land alongside it without
+/// disturbing call sites.
+abstract interface class XWindow {
+  static final XWindow instance = MethodChannelXWindow();
+
+  /// `true` when this app currently has user focus.
+  ///
+  /// - macOS: tracks `NSApplication.didBecomeActiveNotification` /
+  ///   `didResignActiveNotification` via the native plugin.
+  /// - iOS / Android: no native plugin registers, so the emitter stays
+  ///   at its `true` default. That's correct because socket frames only
+  ///   reach the Dart isolate while the process is alive — by the time
+  ///   the OS suspends the app, deliveries have stopped.
+  ValueListenable<bool> get focused;
+}
+
+class MethodChannelXWindow implements XWindow {
+  MethodChannelXWindow() {
+    _events.receiveBroadcastStream().listen(_onEvent, onError: (e, st) {
+      _log.w('event channel error', error: e, stackTrace: st);
+    });
+  }
+
+  static const _events = EventChannel('ux/window/events');
+
+  @override
+  final ValueEmitter<bool> focused = ValueEmitter(true);
+
+  void _onEvent(Object? event) {
+    if (event is! Map) return;
+    final m = event.cast<Object?, Object?>();
+    if (m['type'] == 'focus') {
+      final f = m['focused'];
+      if (f is bool) focused.value = f;
+    }
+  }
+}

lib/ux.dart

@@ -20,6 +20,7 @@ export 'src/video/x_video_player_channel.dart' show MethodChannelXVideoPlayerBac
 export 'src/video/x_video_player_view.dart' show XVideoPlayerView;
 export 'src/clipboard.dart';
 export 'src/notifications/x_notifications.dart';
+export 'src/window/x_window.dart';
 export 'src/file.dart';
 export 'src/gallery.dart';
 export 'src/keyboard.dart';

macos/Classes/NotificationsPlugin.swift

@@ -2,10 +2,10 @@ import AppKit
 import FlutterMacOS
 import UserNotifications
 
-/// `ux/notifications` + `ux/notifications/events`. Generic OS-notification
-/// + app-focus surface used by hosts that want native Notification Center
-/// entries on macOS. Domain-agnostic — the Dart caller decides when to
-/// emit and how to format the payload.
+/// `ux/notifications` + `ux/notifications/events`. Domain-agnostic native
+/// OS-notification surface: show / cancel via the method channel, tap +
+/// authorization changes via the event channel. Window-focus state lives
+/// in `WindowPlugin` (see `XWindow` on the Dart side).
 public class NotificationsPlugin: NSObject, NativePlugin, FlutterStreamHandler,
     UNUserNotificationCenterDelegate
 {
@@ -31,7 +31,6 @@ public class NotificationsPlugin: NSObject, NativePlugin, FlutterStreamHandler,
         eventChannel = events
 
         UNUserNotificationCenter.current().delegate = self
-        observeAppActivation()
     }
 
     // MARK: - FlutterStreamHandler
@@ -41,9 +40,6 @@ public class NotificationsPlugin: NSObject, NativePlugin, FlutterStreamHandler,
         eventSink events: @escaping FlutterEventSink
     ) -> FlutterError? {
         eventSink = events
-        // Seed the initial focus state so Dart-side starts in a deterministic
-        // value rather than the constructor default.
-        emit(["type": "focus", "focused": NSApp.isActive])
         return nil
     }
 
@@ -171,32 +167,6 @@ public class NotificationsPlugin: NSObject, NativePlugin, FlutterStreamHandler,
         }
     }
 
-    // MARK: - App-activation observers
-
-    private func observeAppActivation() {
-        let nc = NotificationCenter.default
-        nc.addObserver(
-            self,
-            selector: #selector(onDidBecomeActive),
-            name: NSApplication.didBecomeActiveNotification,
-            object: nil,
-        )
-        nc.addObserver(
-            self,
-            selector: #selector(onDidResignActive),
-            name: NSApplication.didResignActiveNotification,
-            object: nil,
-        )
-    }
-
-    @objc private func onDidBecomeActive() {
-        emit(["type": "focus", "focused": true])
-    }
-
-    @objc private func onDidResignActive() {
-        emit(["type": "focus", "focused": false])
-    }
-
     // MARK: - UNUserNotificationCenterDelegate
 
     public func userNotificationCenter(

macos/Classes/WindowPlugin.swift

@@ -0,0 +1,68 @@
+import AppKit
+import FlutterMacOS
+
+/// `ux/window/events`. Reports host-application focus state — emits
+/// `{type: "focus", focused: Bool}` whenever the active NSApplication
+/// flips. Seeded from `NSApp.isActive` when Dart subscribes so the
+/// emitter starts in a deterministic value.
+public class WindowPlugin: NSObject, NativePlugin, FlutterStreamHandler {
+    private var eventChannel: FlutterEventChannel?
+    private var eventSink: FlutterEventSink?
+
+    public func register(with registrar: FlutterPluginRegistrar) {
+        let events = FlutterEventChannel(
+            name: "ux/window/events",
+            binaryMessenger: registrar.messenger,
+        )
+        events.setStreamHandler(self)
+        eventChannel = events
+
+        observeAppActivation()
+    }
+
+    // MARK: - FlutterStreamHandler
+
+    public func onListen(
+        withArguments arguments: Any?,
+        eventSink events: @escaping FlutterEventSink
+    ) -> FlutterError? {
+        eventSink = events
+        emit(["type": "focus", "focused": NSApp.isActive])
+        return nil
+    }
+
+    public func onCancel(withArguments arguments: Any?) -> FlutterError? {
+        eventSink = nil
+        return nil
+    }
+
+    // MARK: - Observers
+
+    private func observeAppActivation() {
+        let nc = NotificationCenter.default
+        nc.addObserver(
+            self,
+            selector: #selector(onDidBecomeActive),
+            name: NSApplication.didBecomeActiveNotification,
+            object: nil,
+        )
+        nc.addObserver(
+            self,
+            selector: #selector(onDidResignActive),
+            name: NSApplication.didResignActiveNotification,
+            object: nil,
+        )
+    }
+
+    @objc private func onDidBecomeActive() {
+        emit(["type": "focus", "focused": true])
+    }
+
+    @objc private func onDidResignActive() {
+        emit(["type": "focus", "focused": false])
+    }
+
+    private func emit(_ event: [String: Any]) {
+        eventSink?(event)
+    }
+}

macos/Classes/XPlugin.swift

@@ -13,6 +13,7 @@ public class XPlugin: NSObject, FlutterPlugin {
             UxVideoPlayerPlugin(),
             UrlPlugin(),
             NotificationsPlugin(),
+            WindowPlugin(),
         ]
         for plugin in plugins {
             plugin.register(with: registrar)