[Magmusacy]

Fixes iOS call audio going silent for the rest of a call when other code deactivates the audio session (e.g. expo-audio after playing a sound).

Problem

1. Other code deactivates the shared AVAudioSession.
2. iOS stops WebRTC's VoiceProcessingIO unit.
3. AudioDeviceIOS still has it marked as started, so UpdateAudioUnit never restarts it.

Fix

1. VoiceProcessingAudioUnit listens to kAudioOutputUnitProperty_IsRunning and reports changes through OnRunningStateChanged().
2. AudioDeviceIOS restarts a unit that is marked as started but isn't running, through UpdateAudioUnit (same path as an interruption end).
3. If Stop() fails, it logs and leaves the unit alone.

The restart respects canPlayOrRecord. CallKit hold is handled by the app in fishjam-cloud/fishjam-react-native-webrtc#102.

Testing

iPhone 16 (iOS 26.6.2), fishjam-chat + browser peer:

• Session deactivated (foreground, background, after a sound): audio back after ~0.4 s.
• With #102, CallKit hold → unhold: silent while held, back after ~1 s, peer hears the mic.
• Regular call flows: no regressions.

[Copilot]

Copilot review overview

🟡 Changes recommended

Synthetic public interruption events and an unhandled stop failure can produce inconsistent state or prevent recovery.

Review effort: Balanced
Findings: 2

Open (2)

• Avoid synthetic interruption callbacks for external activation · New
• Handle Stop() failures to ensure audio unit recovery · New

What changed in this PR

Adds recovery for iOS audio units stopped by CallKit or external audio-session changes.

Changes:

• Converts external activation/deactivation into restart signals.
• Monitors VoiceProcessingIO running-state changes.
• Adds interruption-event tests.

File	Description
RTCAudioSessionTest.mm	Tests external session event reporting.
voice_processing_audio_unit.mm	Adds running-state monitoring.
voice_processing_audio_unit.h	Extends observer and unit interfaces.
audio_device_ios.mm	Restarts externally stopped units.
audio_device_ios.h	Declares recovery callbacks.
RTCAudioSession.mm	Emits events for external session changes.

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[Copilot]

🔵 Needs a closer look

A failed running-state query is incorrectly treated as confirmation that the audio unit stopped.

0 open findings

2 resolved since last review

• Handle Stop() failures to ensure audio unit recovery
• Avoid synthetic interruption callbacks for external activation

Previously missed (1)

In code that hasn't changed since last review

Avoid recovery when AudioUnitGetProperty status is unknown

sdk/​objc/​native/​src/​audio/​voice_processing_audio_unit.mm:392

AudioUnitGetProperty failures are indistinguishable from a confirmed stopped state here. The caller consequently invokes Stop() and recovery whenever the query fails, which can interrupt a unit that is still running and obscures the actual Core Audio error. Return the OSStatus separately (for example, via a status return plus an out parameter), log it, and skip recovery unless the query succeeded with is_running == 0.

🧠 Review effort: Balanced