diff --git a/apps/chanora_flutter/ios/Runner/AppDelegate.swift b/apps/chanora_flutter/ios/Runner/AppDelegate.swift
index 6b464ac..4bdcca1 100644
--- a/apps/chanora_flutter/ios/Runner/AppDelegate.swift
+++ b/apps/chanora_flutter/ios/Runner/AppDelegate.swift
@@ -85,6 +85,20 @@ import AVFoundation
       object: nil
     )
 
+    // Diagnostic: subscribe to every AVAudioSession route change so
+    // we can correlate user picker actions with what iOS actually
+    // does to the route. The reason printed here ("override",
+    // "newDeviceAvailable", "categoryChange", etc.) tells us
+    // whether our Dart-side override was honoured or silently
+    // reverted by another component (e.g. cpal's RemoteIO unit
+    // reacting to its own configuration change).
+    NotificationCenter.default.addObserver(
+      self,
+      selector: #selector(handleRouteChange(_:)),
+      name: AVAudioSession.routeChangeNotification,
+      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
@@ -123,11 +137,69 @@ import AVFoundation
     do {
       try AVAudioSession.sharedInstance().setActive(true, options: [])
       NSLog("chanora_flutter: AVAudioSession activated on foreground")
+      logSessionState(tag: "didBecomeActive")
     } catch {
       NSLog("chanora_flutter: AVAudioSession setActive failed: \(error)")
     }
   }
 
+  /// Log the full AVAudioSession state with a diagnostic tag. Used
+  /// after every state transition (setActive, route change) so we
+  /// can correlate user-perceived audio bugs with what iOS thinks
+  /// the session looks like. Output is parseable by grep
+  /// `chanora.session\[`.
+  private func logSessionState(tag: String) {
+    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 preferredInput = s.preferredInput?.portName ?? "<nil>"
+    NSLog("""
+      chanora.session[\(tag)] \
+      cat=\(s.category.rawValue) \
+      mode=\(s.mode.rawValue) \
+      sr=\(s.sampleRate) \
+      ioBuf=\(String(format: "%.4f", s.ioBufferDuration)) \
+      out=[\(outs)] in=[\(ins)] \
+      preferredInput=\(preferredInput)
+      """)
+  }
+
+  /// Called by `routeChangeNotification`. iOS posts this whenever
+  /// the route is reconfigured for any reason — user toggles
+  /// Bluetooth, plugs in headphones, our `overrideOutputAudioPort`
+  /// call, OR (the suspected bug here) when cpal's RemoteIO
+  /// AudioUnit reacts to its own format change and resets the
+  /// route. The `reason` field tells us which case it is:
+  ///
+  ///   * `.override`           : our Dart-side override took effect.
+  ///   * `.routeConfigurationChange` : something else (cpal?)
+  ///                              triggered an internal reconfig.
+  ///   * `.newDeviceAvailable` / `.oldDeviceUnavailable` :
+  ///                              user hardware change.
+  ///   * `.categoryChange`     : someone (us or another app) set a
+  ///                              new category.
+  @objc private func handleRouteChange(_ note: Notification) {
+    guard let reasonValue = note.userInfo?[AVAudioSessionRouteChangeReasonKey] as? UInt,
+          let reason = AVAudioSession.RouteChangeReason(rawValue: reasonValue) else {
+      NSLog("chanora.routeChange[unknown-reason]")
+      return
+    }
+    let reasonName: String
+    switch reason {
+    case .unknown: reasonName = "unknown"
+    case .newDeviceAvailable: reasonName = "newDeviceAvailable"
+    case .oldDeviceUnavailable: reasonName = "oldDeviceUnavailable"
+    case .categoryChange: reasonName = "categoryChange"
+    case .override: reasonName = "override"
+    case .wakeFromSleep: reasonName = "wakeFromSleep"
+    case .noSuitableRouteForCategory: reasonName = "noSuitableRouteForCategory"
+    case .routeConfigurationChange: reasonName = "routeConfigurationChange"
+    @unknown default: reasonName = "default(\(reasonValue))"
+    }
+    logSessionState(tag: "routeChange.\(reasonName)")
+  }
+
   func didInitializeImplicitFlutterEngine(_ engineBridge: FlutterImplicitEngineBridge) {
     GeneratedPluginRegistrant.register(with: engineBridge.pluginRegistry)
   }
diff --git a/apps/chanora_flutter/lib/widgets/voice_compact.dart b/apps/chanora_flutter/lib/widgets/voice_compact.dart
index 67cd5f0..1a59bc1 100644
--- a/apps/chanora_flutter/lib/widgets/voice_compact.dart
+++ b/apps/chanora_flutter/lib/widgets/voice_compact.dart
@@ -766,65 +766,78 @@ class _AudioOutputPickerSheetState extends State<_AudioOutputPickerSheet> {
     }
   }
 
+  /// Diagnostic helper: log the current route's first input and
+  /// output ports with a tag so we can correlate user actions with
+  /// what iOS thinks the route is. Called immediately before an
+  /// override, immediately after, and again 250 ms later to detect
+  /// silent revert.
+  Future<void> _logRoute(String tag) async {
+    try {
+      final route = await AVAudioSession().currentRoute;
+      final outs = route.outputs
+          .map((o) => '${o.portType.name}/${o.portName}')
+          .join(',');
+      final ins = route.inputs
+          .map((i) => '${i.portType.name}/${i.portName}')
+          .join(',');
+      debugPrint('chanora.route[$tag] out=[$outs] in=[$ins]');
+    } catch (e) {
+      debugPrint('chanora.route[$tag] FAILED: $e');
+    }
+  }
+
   Future<void> _selectSpeaker() async {
+    await _logRoute('speaker.before');
     try {
-      // Apple-documented quirk: in .voiceChat mode, calling
-      // setPreferredInput(builtInMic) AFTER overrideOutputAudioPort(.speaker)
-      // causes iOS to recalculate the route. Built-in mic naturally
-      // pairs with the receiver (not the speaker), so the system
-      // SILENTLY REVERTS the speaker override and routes audio
-      // back through the earpiece. Net: the await chain returns
-      // successfully ('no exception'), but the user hears no
-      // change.
-      //
-      // Fix: do NOT call setPreferredInput when forcing speaker.
-      // The speaker override is sufficient on its own \u2014 input
-      // remains on whatever the system was already using (built-in
-      // mic by default, or BT/wired if connected and selected
-      // elsewhere). For consistency, only switch input when the
-      // user explicitly picks a non-speaker input row.
       await AVAudioSession()
           .overrideOutputAudioPort(AVAudioSessionPortOverride.speaker);
-      debugPrint('chanora: audio output -> speakerphone (override applied)');
+      debugPrint('chanora: override(.speaker) returned OK');
     } catch (e, st) {
       debugPrint('chanora: _selectSpeaker FAILED: $e\n$st');
     }
+    await _logRoute('speaker.after');
+    // Schedule a delayed re-check — if cpal's RemoteIO unit reverts
+    // the route on routeChangeNotification, this will surface the
+    // revert (out=builtInReceiver instead of builtInSpeaker).
+    Future.delayed(const Duration(milliseconds: 250), () {
+      _logRoute('speaker.after+250ms');
+    });
     if (!mounted) return;
     Navigator.of(context).pop();
   }
 
   Future<void> _selectReceiver() async {
+    await _logRoute('receiver.before');
     try {
-      // Same quirk in reverse: removing the speaker override
-      // (.none) is enough to restore the .voiceChat default route,
-      // which is the built-in receiver. Calling setPreferredInput
-      // explicitly here is redundant and risks the same recalc
-      // race that broke _selectSpeaker before.
       await AVAudioSession()
           .overrideOutputAudioPort(AVAudioSessionPortOverride.none);
-      debugPrint('chanora: audio output -> receiver (override cleared)');
+      debugPrint('chanora: override(.none) returned OK');
     } catch (e, st) {
       debugPrint('chanora: _selectReceiver FAILED: $e\n$st');
     }
+    await _logRoute('receiver.after');
+    Future.delayed(const Duration(milliseconds: 250), () {
+      _logRoute('receiver.after+250ms');
+    });
     if (!mounted) return;
     Navigator.of(context).pop();
   }
 
   Future<void> _selectInput(AVAudioSessionPortDescription port) async {
+    await _logRoute('input.${port.portType.name}.before');
     try {
-      // Drop any speakerphone override so the route follows the
-      // selected input. BT / wired headset / USB inputs pair their
-      // OWN output (the user hears audio through the same device
-      // they speak into), so .none + setPreferredInput is the
-      // correct combo here.
       await AVAudioSession()
           .overrideOutputAudioPort(AVAudioSessionPortOverride.none);
       await AVAudioSession().setPreferredInput(port);
       debugPrint(
-          'chanora: audio output -> ${port.portName} (${port.portType})');
+          'chanora: setPreferredInput(${port.portName}/${port.portType.name}) OK');
     } catch (e, st) {
       debugPrint('chanora: _selectInput FAILED: $e\n$st');
     }
+    await _logRoute('input.${port.portType.name}.after');
+    Future.delayed(const Duration(milliseconds: 250), () {
+      _logRoute('input.${port.portType.name}.after+250ms');
+    });
     if (!mounted) return;
     Navigator.of(context).pop();
   }