On macOS 27 beta, mpv's coreaudio AO fails to initialize (channel layout
set rejected with paramErr -50). The existing ao=coreaudio,avfoundation
fallback restored audio, but exposed an mpv bug: init() registers a HAL
hotplug listener (AudioObjectAddPropertyListener on the system object,
with the raw ao pointer as user data) before the step that fails, and
the coreaudio_error path never unregisters it. mpv then frees the ao
and falls back to avfoundation, leaving a dangling listener per
playback start. The next audio device change (AirPods connect,
sleep/wake device republish) invokes the listener with the freed
pointer and crashes with a use-after-free SIGSEGV on the
HALC_ProxyNotification Call Listener Queue (observed in build 262;
faulting address was reused "texture_" shader string memory).
Gate the AO order by OS version: on macOS 27+ use
avfoundation,coreaudio so the failing coreaudio init never runs; older
macOS keeps the native coreaudio first with avfoundation as fallback.
Update the read-only defaults mirror in MPV options settings to match.
afa73e6bcb