The library registered no shutdown callback, so a guest mixer thread kept calling sceAudioOut2ContextPush while exit ran the static destructors and mixed from the freed port table (#5864). Exports that read the port tables or output audio now hold a guard: once exit starts they park the thread with LibcAwaitExit_nid_postfix, and the shutdown callback waits for the calls already inside. A push waiting for a grain from sceAudioOut2ContextAdvance also wakes on the shutdown token, so the callback does not wait for an advance that is parked.
