fix(ios): break audio session route-change feedback loop

handleRouteChange called applyConfiguration() unconditionally, which called
setCategory/setPreferredInput/etc., which triggered another route-change
notification, which called applyConfiguration() again — an infinite loop that
burned CPU (phone slowdown) and repeatedly tore down/rebuilt the audio session
(audio cycling on/off, VoiceOver glitching).

Two fixes:
1. handleRouteChange now only re-applies config on external device changes
   (.oldDeviceUnavailable / .newDeviceAvailable), not on .categoryChange /
   .routeConfigurationChange which are triggered by our own setCategory calls.
2. IOSAudioRouter.applyConfiguration() gained a re-entrancy guard
   (isApplyingConfiguration) for synchronous route-change notifications.

Also added os.Logger logging to both files (subsystem cat.voice.VoiceCatiOS)
so future issues can be debugged from Console.app on the Mac.

clients/apple/iOS/VoiceCatiOS/IOSAudioRouter.swift

@@ -1,6 +1,9 @@
 import AVFoundation
+import os
 import VoiceCatCore
 
+private let logger = Logger(subsystem: "cat.voice.VoiceCatiOS", category: "IOSAudioRouter")
+
 /// iOS audio routing layer — drives all iOS audio route selection via `AVAudioSession`
 /// *before* the core (miniaudio) opens its device. miniaudio does NOT touch
 /// `AVAudioSession` on iOS; it opens the current default route via CoreAudio and that's
@@ -75,6 +78,13 @@ final class IOSAudioRouter: ObservableObject {
     private let kDataSourceId = "cat.voice.audio.dataSourceId"
     private let kPolarPattern = "cat.voice.audio.polarPattern"
 
+    /// Re-entrancy guard: setCategory/setPreferredInput/etc. trigger route-change
+    /// notifications synchronously on the same thread. Without this guard,
+    /// handleRouteChange → applyConfiguration → setCategory → route-change notification
+    /// → handleRouteChange → applyConfiguration → ... creates an infinite loop that
+    /// burns CPU and cycles the audio session on/off (the "glitching" bug).
+    private var isApplyingConfiguration = false
+
     private init() {}
 
     // MARK: - Load / refresh from AVAudioSession
@@ -131,7 +141,16 @@ final class IOSAudioRouter: ObservableObject {
 
     /// Apply the full audio configuration to AVAudioSession. Call this before the core
     /// opens its capture device (i.e. before `startMicStream` → `activateForStreaming`).
+    /// Re-entrant-safe: if a route-change notification fires synchronously during a
+    /// `setCategory`/`setPreferredInput` call, the guard prevents re-entry.
     func applyConfiguration() {
+        guard !isApplyingConfiguration else {
+            logger.debug("applyConfiguration skipped — already applying (re-entrancy guard)")
+            return
+        }
+        isApplyingConfiguration = true
+        defer { isApplyingConfiguration = false }
+
         let session = AVAudioSession.sharedInstance()
 
         // 1. Build category options from bluetooth mode.
@@ -159,8 +178,9 @@ final class IOSAudioRouter: ObservableObject {
 
         do {
             try session.setCategory(.playAndRecord, mode: mode, options: options)
+            logger.info("setCategory ok — mode=\(self.modeLabel(mode)), bt=\(self.bluetoothMode.rawValue)")
         } catch {
-            print("[IOSAudioRouter] setCategory failed: \(error)")
+            logger.error("setCategory failed: \(error.localizedDescription)")
         }
 
         // 3. Set preferred input port.
@@ -168,8 +188,9 @@ final class IOSAudioRouter: ObservableObject {
            let port = session.availableInputs?.first(where: { $0.uid == portId }) {
             do {
                 try session.setPreferredInput(port)
+                logger.info("setPreferredInput ok — \(port.portName)")
             } catch {
-                print("[IOSAudioRouter] setPreferredInput failed: \(error)")
+                logger.error("setPreferredInput failed: \(error.localizedDescription)")
             }
 
             // 4. Set preferred data source (orientation) on the selected input port.
@@ -177,8 +198,9 @@ final class IOSAudioRouter: ObservableObject {
                let dataSource = port.dataSources?.first(where: { String(describing: $0.dataSourceID) == dataSourceId }) {
                 do {
                     try port.setPreferredDataSource(dataSource)
+                    logger.info("setPreferredDataSource ok — \(dataSource.dataSourceName)")
                 } catch {
-                    print("[IOSAudioRouter] setPreferredDataSource failed: \(error)")
+                    logger.error("setPreferredDataSource failed: \(error.localizedDescription)")
                 }
 
                 // 5. Set preferred polar pattern on the data source.
@@ -186,8 +208,9 @@ final class IOSAudioRouter: ObservableObject {
                     let pattern = AVAudioSession.PolarPattern(rawValue: polarPattern)
                     do {
                         try dataSource.setPreferredPolarPattern(pattern)
+                        logger.info("setPreferredPolarPattern ok — \(polarPattern)")
                     } catch {
-                        print("[IOSAudioRouter] setPreferredPolarPattern failed: \(error)")
+                        logger.error("setPreferredPolarPattern failed: \(error.localizedDescription)")
                     }
                 }
             }
@@ -196,13 +219,22 @@ final class IOSAudioRouter: ObservableObject {
         // 6. Set preferred input number of channels (stereo capture).
         do {
             try session.setPreferredInputNumberOfChannels(Int(captureChannels.channelCount))
+            logger.info("setPreferredInputNumberOfChannels ok — \(self.captureChannels.rawValue)")
         } catch {
-            print("[IOSAudioRouter] setPreferredInputNumberOfChannels failed: \(error)")
+            logger.error("setPreferredInputNumberOfChannels failed: \(error.localizedDescription)")
         }
 
         updateRawModeWarning()
     }
 
+    private func modeLabel(_ mode: AVAudioSession.Mode) -> String {
+        switch mode {
+        case .voiceChat: return "voiceChat"
+        case .measurement: return "measurement"
+        default: return "other"
+        }
+    }
+
     /// Apply stored preferences from UserDefaults. Called at app launch (before any
     /// audio session activation).
     func loadStoredPreferences() {