pub fn restart_audio_engine_child() -> Result<(), String>Expand description
Drop the long-lived audio-engine child so the next IPC spawns a fresh process.
Use after a crash or when the AudioEngine stops responding.
Returns immediately after sending SIGKILL so the UI / toast is not blocked by mutex cleanup
(which can take many seconds if an IPC thread still holds ENGINE_CHILD). Reaping runs on
a background thread; the next spawn_audio_engine_request will spawn a fresh child if needed.