Fix iOS stereo microphone capture

PROGRESS.md

@@ -19,10 +19,11 @@ The source-of-truth layout is:
 - `native/media/` and `native/rnnoise/` — required Opus/RNNoise shim and vendored RNNoise.
 - `native/apple/broadcast/` — required ReplayKit upload extension and shared ring producer.
 
-The physical-device iOS voice path now supports ReplayKit fallback and stable Apple VPIO
-voice-chat capture using a paced 20 ms handoff. Stereo microphone routing remains an open device
-gate: the stereo preset currently receives duplicated mono samples despite selecting the built-in
-stereo capsule.
+The physical-device iOS voice path now supports ReplayKit fallback, stable Apple VPIO voice-chat
+capture using a paced 20 ms handoff, and true built-in stereo microphone capture. Stereo was
+verified on an iPhone 16 Pro Max with a two-channel AVAudioEngine input and distinct left/right
+samples; the managed Apple binding requires native use of its otherwise-unmapped stereo polar
+pattern constant.
 
 ## Release gates
 
@@ -30,8 +31,8 @@ stereo capsule.
   20/40/60 ms buffering, duration-aware DRED/FEC, and mismatched input/output endpoints.
 - Complete NVDA and VoiceOver navigation/announcement passes.
 - Exercise iOS background/lock, interruption, Bluetooth, route-change, ReplayKit, and iOS 27
-  ScreenCaptureKit paths on devices. Verify distinct left/right capture with the stereo microphone
-  preset, including changing mono/stereo while joined, and Windows desktop/per-app stereo sharing.
+  ScreenCaptureKit paths on devices. Complete extended mono/stereo/voice-chat switching while
+  joined, and verify Windows desktop/per-app stereo sharing.
 - Complete Developer ID signing/notarization. The iOS host and ReplayKit extension have been
   distribution-signed and packaged locally; upload the IPA for Apple's server-side validation.
 - Run the published Linux container and a 30-minute-or-longer server soak.