fix(ios audio): route earpiece reliably; stop fighting WebKit's audio session

Speaker worked but the earpiece was silent, and call audio flickered on speaker
then dropped. Causes: (1) the category set .defaultToSpeaker, so overrideOutputAudioPort(.none)
fell back to the loudspeaker instead of the receiver; (2) setSpeaker re-ran
setCategory+setActive on every toggle mid-call, tearing down the audio unit WebKit's
WebRTC engine was using and silencing the earpiece route.

Fix: drop .defaultToSpeaker (drive the port explicitly), make setSpeaker flip ONLY
overrideOutputAudioPort, and observe routeChangeNotification to re-assert the chosen
route when WebKit reconfigures the session at call start / device change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

mobile/plugins/audio-route/ios/Sources/AudioRoutePlugin/AudioRoutePlugin.swift

@@ -2,9 +2,19 @@ import Foundation
 import Capacitor
 import AVFoundation
 
-// Earpiece <-> speaker toggle for calls. Registered by cap sync as a normal Capacitor plugin package, so it
-// appears as window.Capacitor.Plugins.AudioRoute (unlike an app-embedded class, which gets stripped/not
-// discovered in release builds). setSpeaker({on}) overrides the AVAudioSession output port.
+// Earpiece <-> speaker toggle for calls. Registered by cap sync as a real Capacitor plugin package, so it
+// shows up as window.Capacitor.Plugins.AudioRoute (an app-embedded class gets stripped in release builds).
+//
+// WHY THIS SHAPE (earlier version left the earpiece silent):
+//  * The category is configured WITHOUT .defaultToSpeaker, so overrideOutputAudioPort(.none) reliably means
+//    the earpiece/receiver. WITH .defaultToSpeaker, .none falls back to the loudspeaker and the earpiece
+//    never receives audio.
+//  * setSpeaker flips ONLY overrideOutputAudioPort. It must NOT re-setCategory/setActive mid-call: doing so
+//    tears down the audio unit WebKit's WebRTC engine is actively using and leaves the earpiece route silent
+//    (forcing .speaker is a strong enough override to survive it, which is why only speaker "worked").
+//  * WebKit reconfigures the shared AVAudioSession when call audio starts (and on headset plug/unplug), which
+//    would clobber our choice — so we observe routeChangeNotification and re-assert the desired port. That
+//    also removes the "call starts on speaker then drops to silence" flicker.
 @objc(AudioRoutePlugin)
 public class AudioRoutePlugin: CAPPlugin, CAPBridgedPlugin {
     public let identifier = "AudioRoutePlugin"
@@ -13,21 +23,56 @@ public class AudioRoutePlugin: CAPPlugin, CAPBridgedPlugin {
         CAPPluginMethod(name: "setSpeaker", returnType: CAPPluginReturnPromise)
     ]
 
+    // Desired output — the source of truth, re-applied on every route change. Defaults to earpiece; the JS
+    // side calls setSpeaker(true) at call start when it wants the loudspeaker (meetRoute defaults to 'speaker').
+    private var wantSpeaker = false
+
     override public func load() {
-        // Default calls to the loudspeaker when the plugin initialises (iOS uses the quiet earpiece otherwise).
         let session = AVAudioSession.sharedInstance()
-        try? session.setCategory(.playAndRecord, mode: .voiceChat, options: [.defaultToSpeaker, .allowBluetooth, .allowBluetoothA2DP])
+        // NO .defaultToSpeaker — the output port is driven explicitly (see note above).
+        try? session.setCategory(.playAndRecord, mode: .voiceChat, options: [.allowBluetooth, .allowBluetoothA2DP])
         try? session.setActive(true)
+        NotificationCenter.default.addObserver(self, selector: #selector(routeChanged(_:)),
+                                               name: AVAudioSession.routeChangeNotification, object: nil)
+    }
+
+    deinit {
+        NotificationCenter.default.removeObserver(self)
+    }
+
+    // WebKit/WebRTC reset the route (call audio just started, or a headset was (un)plugged). Re-assert ours,
+    // but ignore the change we caused ourselves (.override) so we don't fight in a feedback loop.
+    @objc private func routeChanged(_ note: Notification) {
+        if let info = note.userInfo,
+           let raw = info[AVAudioSessionRouteChangeReasonKey] as? UInt,
+           let reason = AVAudioSession.RouteChangeReason(rawValue: raw),
+           reason == .override {
+            return
+        }
+        applyRoute()
+    }
+
+    // Nudge the port toward the desired output, but only when it actually differs — this leaves an attached
+    // Bluetooth/wired headset alone in the earpiece case (its route is neither builtInSpeaker nor forced).
+    private func applyRoute() {
+        let session = AVAudioSession.sharedInstance()
+        let onSpeaker = session.currentRoute.outputs.contains { $0.portType == .builtInSpeaker }
+        do {
+            if wantSpeaker && !onSpeaker {
+                try session.overrideOutputAudioPort(.speaker)
+            } else if !wantSpeaker && onSpeaker {
+                try session.overrideOutputAudioPort(.none)
+            }
+        } catch { }
     }
 
     @objc func setSpeaker(_ call: CAPPluginCall) {
-        let on = call.getBool("on") ?? true
+        wantSpeaker = call.getBool("on") ?? true
         let session = AVAudioSession.sharedInstance()
         do {
-            try session.setCategory(.playAndRecord, mode: .voiceChat, options: [.allowBluetooth, .allowBluetoothA2DP])
-            try session.setActive(true)
-            try session.overrideOutputAudioPort(on ? .speaker : .none)
-            call.resolve(["route": on ? "speaker" : "earpiece"])
+            // Flip ONLY the output port. No setCategory/setActive here — that would disrupt WebKit's audio.
+            try session.overrideOutputAudioPort(wantSpeaker ? .speaker : .none)
+            call.resolve(["route": wantSpeaker ? "speaker" : "earpiece"])
         } catch {
             call.reject(error.localizedDescription)
         }