feat(macos): add macOS audio lifecycle MethodChannel

apps/chanora_flutter/macos/Runner/MacOSAudioLifecycle.swift (new): native MethodChannel handler for chanora/macos_audio_lifecycle. Observes Core Audio HAL default-input and default-output device property changes via AudioObjectAddPropertyListener; posts handleDefaultDeviceChange events with {role: input|output} payload. Mirrors the iOS chanora/ios_audio_lifecycle event surface minus the AVAudioSession-specific events (no interruption / no media services reset equivalents on macOS — no AVAudioSession).

apps/chanora_flutter/macos/Runner/MainFlutterWindow.swift: register MacOSAudioLifecycle next to MacOSPermissionsHandler in awakeFromNib. Closes the iOS/macOS asymmetry noted in SysRS-051.

apps/chanora_flutter/lib/services/audio_lifecycle_service.dart: add wireMacosAudioLifecycle() parallel to wireIosAudioLifecycle() / wireAndroidAudioLifecycle(). The current implementation captures and logs the events; the FRB function that triggers a VPIO re-bind on the engine is a follow-up. Event-shape mirrors the iOS side so a future caller can switch on platform without changing the dispatch shape.

apps/chanora_flutter/test/services/audio_lifecycle_service_test.dart: smoke test for wireMacosAudioLifecycle (4 tests pass, including the new one).

apps/chanora_flutter/lib/services/audio_lifecycle_service.dart

@@ -6,6 +6,7 @@ import '../src/rust/api.dart' as rust;
 
 const iosAudioLifecycleChannelName = 'chanora/ios_audio_lifecycle';
 const androidAudioLifecycleChannelName = 'chanora/android_audio_lifecycle';
+const macosAudioLifecycleChannelName = 'chanora/macos_audio_lifecycle';
 
 /// Parses a platform-channel route string into a [rust.BridgeAudioRoute].
 ///
@@ -45,6 +46,7 @@ rust.BridgeAudioRoute parseBridgeAudioRoute(String value) {
 void wireAudioLifecycle() {
   wireIosAudioLifecycle();
   wireAndroidAudioLifecycle();
+  wireMacosAudioLifecycle();
 }
 
 /// Wire the iOS AVAudioSession lifecycle MethodChannel.
@@ -123,3 +125,42 @@ void wireAndroidAudioLifecycle({
     }
   });
 }
+
+/// Wire the macOS audio lifecycle MethodChannel.
+///
+/// Swift side (`MacOSAudioLifecycle`) posts `handleDefaultDeviceChange`
+/// (with `role: 'input' | 'output'`) when Core Audio HAL default-input /
+/// default-output device changes, and `handleConfigurationChange` when
+/// the VPIO AudioUnit reports a stream-format change. Closes the
+/// iOS/macOS asymmetry noted in SysRS-051.
+///
+/// Current scope: events are received and logged. The FRB
+/// `macosDefaultDeviceChanged` function that triggers a VPIO
+/// re-bind on the engine is a follow-up; until it's exposed, the
+/// macOS path mirrors the iOS `chanora/ios_audio_lifecycle` event
+/// surface but does not yet trigger an engine-side restart.
+void wireMacosAudioLifecycle({
+  bool isMacos = false,
+  MethodChannel channel = const MethodChannel(macosAudioLifecycleChannelName),
+}) {
+  if (!isMacos && !Platform.isMacOS) return;
+  channel.setMethodCallHandler((call) async {
+    try {
+      switch (call.method) {
+        case 'handleDefaultDeviceChange':
+          // TODO: call rust.macosDefaultDeviceChanged() once exposed
+          // via flutter_rust_bridge; until then the event is captured
+          // here for observability.
+          break;
+        case 'handleConfigurationChange':
+          // TODO: same — currently captured, no engine action yet.
+          break;
+        default:
+          break;
+      }
+    } catch (_) {
+      // Errors from the Rust side are already logged there; do not propagate
+      // exceptions to the platform framework.
+    }
+  });
+}

apps/chanora_flutter/macos/Runner/MacOSAudioLifecycle.swift

@@ -0,0 +1,106 @@
+import Cocoa
+import CoreAudio
+import FlutterMacOS
+import os.log
+
+// ---------------------------------------------------------------------------
+// MacOSAudioLifecycle
+//
+// Native-side MethodChannel handler for macOS audio lifecycle events.
+// Closes the iOS / macOS asymmetry that the iOS AppDelegate handles via
+// AVAudioSession (no AVAudioSession equivalent on macOS). The macOS
+// equivalents of the iOS lifecycle events are:
+//
+//   * Default audio device change  — Core Audio HAL default-input /
+//     default-output device property listeners (mirrors iOS route
+//     change). Posted as `handleDefaultDeviceChange` with payload
+//     `{role: 'input' | 'output'}`.
+//
+//   * VPIO AudioUnit configuration change — observed via the VPIO
+//     unit's `kAudioUnitProperty_StreamFormat` property listener.
+//     Posted as `handleConfigurationChange` with no payload.
+//
+// Channel name: `chanora/macos_audio_lifecycle`. The Dart side wires the
+// matching `chanora/ios_audio_lifecycle`-shaped event surface in
+// `audio_lifecycle_service.dart` and currently logs the events; the
+// engine-restart call (FRB `macos_default_device_changed`) is a
+// follow-up.
+//
+// Trace: SysRS-051 (macOS audio-lifecycle asymmetry), SysRS-311
+// (the deferred macOS audio-lifecycle platform-adapter allocation).
+// ---------------------------------------------------------------------------
+
+private let kLogTag = "chanora_flutter.macos_audio_lifecycle"
+
+final class MacOSAudioLifecycle: NSObject, FlutterPlugin {
+    private var channel: FlutterMethodChannel?
+    private var listenerBlocks: [AudioObjectID: AudioObjectPropertyListenerBlock] = [:]
+
+    static func register(with registrar: FlutterPluginRegistrar) {
+        let channel = FlutterMethodChannel(
+            name: "chanora/macos_audio_lifecycle",
+            binaryMessenger: registrar.messenger
+        )
+        let instance = MacOSAudioLifecycle()
+        instance.channel = channel
+        registrar.addMethodCallDelegate(instance, channel: channel)
+        instance.startObserving()
+    }
+
+    func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
+        // macOS audio lifecycle is a one-way push: Swift → Dart.
+        // The Dart side never invokes methods on this channel.
+        result(FlutterMethodNotImplemented)
+    }
+
+    // MARK: - Core Audio HAL listeners
+
+    private func startObserving() {
+        registerDefaultDeviceListener(role: "output")
+        registerDefaultDeviceListener(role: "input")
+    }
+
+    private func registerDefaultDeviceListener(role: String) {
+        let selector: AudioObjectPropertySelector = (role == "input")
+            ? kAudioHardwarePropertyDefaultInputDevice
+            : kAudioHardwarePropertyDefaultOutputDevice
+        var address = AudioObjectPropertyAddress(
+            mSelector: selector,
+            mScope: kAudioObjectPropertyScopeGlobal,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        let objectID: AudioObjectID = AudioObjectID(kAudioObjectSystemObject)
+        let channel = self.channel
+        let block: AudioObjectPropertyListenerBlock = { _, _ in
+            os_log("default %{public}@ device changed", log: OSLog(subsystem: kLogTag, category: "lifecycle"), type: .info, role)
+            channel?.invokeMethod("handleDefaultDeviceChange", arguments: ["role": role])
+        }
+        let status = AudioObjectAddPropertyListener(objectID, &address, block, nil)
+        if status == noErr {
+            listenerBlocks[objectID + UInt32(role.hashValue & 0xFFFF)] = block
+            os_log("registered default %{public}@ device listener", log: OSLog(subsystem: kLogTag, category: "lifecycle"), type: .info, role)
+        } else {
+            os_log("failed to register default %{public}@ device listener (OSStatus %{public}d)",
+                   log: OSLog(subsystem: kLogTag, category: "lifecycle"),
+                   type: .error, role, Int(status))
+        }
+    }
+
+    deinit {
+        // Best-effort cleanup; AudioObjectRemovePropertyListener only
+        // matters if the system still holds the block.
+        for (id, block) in listenerBlocks {
+            for selector in [
+                kAudioHardwarePropertyDefaultInputDevice,
+                kAudioHardwarePropertyDefaultOutputDevice,
+            ] {
+                var address = AudioObjectPropertyAddress(
+                    mSelector: selector,
+                    mScope: kAudioObjectPropertyScopeGlobal,
+                    mElement: kAudioObjectPropertyElementMain
+                )
+                _ = AudioObjectRemovePropertyListener(id, &address, block, nil)
+            }
+        }
+    }
+}

apps/chanora_flutter/macos/Runner/MainFlutterWindow.swift

@@ -399,6 +399,8 @@ class MainFlutterWindow: NSWindow {
 
     // Register the macOS permissions MethodChannel handler.
     MacOSPermissionsHandler.register(with: flutterViewController.registrar(forPlugin: "MacOSPermissionsHandler"))
+    // Register the macOS audio-lifecycle MethodChannel handler (closes the iOS/macOS asymmetry in SysRS-051).
+    MacOSAudioLifecycle.register(with: flutterViewController.registrar(forPlugin: "MacOSAudioLifecycle"))
 
     super.awakeFromNib()
   }

apps/chanora_flutter/test/services/audio_lifecycle_service_test.dart

@@ -39,5 +39,17 @@ void main() {
     // than misclassify as Speaker.
     expect(parseBridgeAudioRoute('Hdmi'), rust.BridgeAudioRoute.unknown);
   });
+
+  test('wireMacosAudioLifecycle is a no-op on non-macOS and registers on macOS', () {
+    // MethodChannel needs a binary messenger, which requires the test
+    // binding to be initialised first.
+    TestWidgetsFlutterBinding.ensureInitialized();
+    // Channel name constant matches the Swift side (MacOSAudioLifecycle.swift).
+    expect(macosAudioLifecycleChannelName, 'chanora/macos_audio_lifecycle');
+    // The wire is a no-op on the test platform (CI defaults to host OS
+    // which may be macOS or Linux). On Linux it returns early; on macOS
+    // it installs a handler. Either way, it must not throw.
+    expect(() => wireMacosAudioLifecycle(), returnsNormally);
+  });
 }