feat(ios,p0): iOS P0 platform, audio fixes, channel UX

apps/chanora_flutter/ios/Runner/AppDelegate.swift

@@ -4,6 +4,8 @@ import AVFoundation
 
 @main
 @objc class AppDelegate: FlutterAppDelegate, FlutterImplicitEngineDelegate {
+  private var iosAudioLifecycleChannel: FlutterMethodChannel?
+
   override func application(
     _ application: UIApplication,
     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
@@ -98,7 +100,10 @@ import AVFoundation
         //                         output-only Bluetooth devices.
         options: [.defaultToSpeaker, .allowBluetoothHFP, .allowBluetoothA2DP]
       )
-      NSLog("chanora_flutter: AVAudioSession category set (playAndRecord/default + defaultToSpeaker)")
+      // Match VPIO / Opus frame cadence to reduce callback pressure.
+      try session.setPreferredIOBufferDuration(0.02)
+      try session.setPreferredSampleRate(48000.0)
+      logAudioSessionState(context: "setCategory")
     } catch {
       NSLog("chanora_flutter: AVAudioSession setCategory failed: \(error)")
     }
@@ -115,6 +120,20 @@ import AVFoundation
       object: nil
     )
 
+    NotificationCenter.default.addObserver(
+      self,
+      selector: #selector(handleRouteChange(_:)),
+      name: AVAudioSession.routeChangeNotification,
+      object: nil
+    )
+
+    NotificationCenter.default.addObserver(
+      self,
+      selector: #selector(handleInterruption(_:)),
+      name: AVAudioSession.interruptionNotification,
+      object: nil
+    )
+
     // Request microphone access on first launch rather than waiting
     // for the user's first voice-channel join. The latter is
     // surprising: the user has only tapped "connect to server" and
@@ -161,17 +180,13 @@ import AVFoundation
       // 44.1 kHz (which would explain the user's broken playback
       // \u2014 our render callback would be writing samples at the
       // wrong rate, causing pitch + timing artifacts).
+      logAudioSessionState(context: "setActive")
       let s = AVAudioSession.sharedInstance()
-      let route = s.currentRoute
-      let outs = route.outputs.map { "\($0.portType.rawValue)/\($0.portName)" }.joined(separator: ",")
-      let ins = route.inputs.map { "\($0.portType.rawValue)/\($0.portName)" }.joined(separator: ",")
+      let ins = s.currentRoute.inputs.map { "\($0.portType.rawValue)/\($0.portName)" }.joined(separator: ",")
       NSLog(
         "chanora_flutter: AVAudioSession actual: " +
-        "category=\(s.category.rawValue) " +
-        "mode=\(s.mode.rawValue) " +
         "sampleRate=\(s.sampleRate) " +
         "ioBufferDuration=\(String(format: "%.4f", s.ioBufferDuration)) " +
-        "outputs=[\(outs)] " +
         "inputs=[\(ins)] " +
         "outputVolume=\(s.outputVolume)"
       )
@@ -180,7 +195,65 @@ import AVFoundation
     }
   }
 
+  /// Reads back the actual AVAudioSession state and logs it for
+  /// SDD-098 compliance. Called after both setCategory and setActive
+  /// to verify that the session accepted the requested configuration.
+  private func logAudioSessionState(context: String) {
+    let s = AVAudioSession.sharedInstance()
+    NSLog("chanora_flutter: [\(context)] category=\(s.category.rawValue) mode=\(s.mode.rawValue) options=\(s.categoryOptions.rawValue) route outputs=\(s.currentRoute.outputs.map { "\($0.portType.rawValue)" })")
+    if s.sampleRate != 48000.0 {
+      NSLog("chanora_flutter: WARNING: actual sample rate \(s.sampleRate) != requested 48000")
+    }
+    if s.ioBufferDuration > 0.025 {
+      NSLog("chanora_flutter: WARNING: IO buffer duration \(s.ioBufferDuration) > 25ms, may cause latency")
+    }
+  }
+
+  @objc private func handleRouteChange(_ notification: Notification) {
+    guard let userInfo = notification.userInfo,
+          let reasonValue = userInfo[AVAudioSessionRouteChangeReasonKey] as? UInt,
+          let reason = AVAudioSession.RouteChangeReason(rawValue: reasonValue)
+    else {
+      return
+    }
+
+    let routeDescription = AVAudioSession.sharedInstance().currentRoute
+    let outputs = routeDescription.outputs.map { $0.portType.rawValue }.joined(separator: ",")
+    NSLog("chanora_flutter: route change reason=\(reason.rawValue) outputs=\(outputs)")
+
+    if reason == .oldDeviceUnavailable || reason == .newDeviceAvailable {
+      iosAudioLifecycleChannel?.invokeMethod("handleRouteChange", arguments: nil)
+    }
+  }
+
+  @objc private func handleInterruption(_ notification: Notification) {
+    guard let userInfo = notification.userInfo,
+          let typeValue = userInfo[AVAudioSessionInterruptionTypeKey] as? UInt,
+          let type = AVAudioSession.InterruptionType(rawValue: typeValue)
+    else {
+      return
+    }
+
+    switch type {
+    case .began:
+      NSLog("chanora_flutter: audio interruption began")
+      iosAudioLifecycleChannel?.invokeMethod("handleInterruptionBegan", arguments: nil)
+    case .ended:
+      let shouldResume = (userInfo[AVAudioSessionInterruptionOptionKey] as? UInt)
+        .map { $0 & AVAudioSession.InterruptionOptions.shouldResume.rawValue != 0 }
+        ?? false
+      NSLog("chanora_flutter: audio interruption ended shouldResume=\(shouldResume)")
+      iosAudioLifecycleChannel?.invokeMethod("handleInterruptionEnded", arguments: shouldResume)
+    @unknown default:
+      break
+    }
+  }
+
   func didInitializeImplicitFlutterEngine(_ engineBridge: FlutterImplicitEngineBridge) {
     GeneratedPluginRegistrant.register(with: engineBridge.pluginRegistry)
+    iosAudioLifecycleChannel = FlutterMethodChannel(
+      name: "chanora/ios_audio_lifecycle",
+      binaryMessenger: engineBridge.applicationRegistrar.messenger()
+    )
   }
 }