Two on-device bugs in the native iOS Voice-Processing path (Swift-only;
no core/ABI change).
1. Voice Chat (VPIO) silent playback: doStartMicStream() called
audioRestart() BEFORE startStream, so when the engine was already
running (a remote stream had started it) it reopened with
external_capture=false and opened a hardware miniaudio capture device.
The announce-result restart then early-returns (engine already running)
so that device was never dropped and fought the AVAudioEngine VPIO unit,
silencing playback. Now: setExternalPlayback first, then startStream
(stores external_feed synchronously), THEN audioRestart() — the core
reopens in full external mode (no hardware devices). Added VPIO
diagnostics: graph/route formats at start, ring written/read totals at
teardown.
2. Stereo Mic / Studio quiet earpiece: the .builtInMicBtA2dp presets omit
.defaultToSpeaker (it breaks A2DP) and skip forceSpeaker, so with no
Bluetooth connected output pinned to the quiet receiver. New
IOSAudioRouter.applyA2dpSpeakerFallback() overrides to the built-in
speaker when no external (A2DP/wired/AirPlay) output is present and
clears the override when one is — called after activation and on
device-change route changes.