Local macOS runtime update — 12 October 2026

Port the applicable shared-runtime changes from the Linux native-port review:
heap boundary/overflow/slot reuse, concurrent overlay paths, thread resource
lifetime, graphics-interface cleanup, faster audio sampling and message removal.
Use a checked immutable dispatch table and free VM gaps where not already present.
Preserve the existing native Metal renderer, CoreAudio, edition handling and
Apple Silicon memory-protection behavior. DirectPlay 8 fragmentation, DirectDraw
conversion and Vulkan guest ownership/cache fixes apply where modules exist.

Validation: recomp/tests/runtime_regressions_macos.py runs portable synthetic
regressions with AddressSanitizer and UndefinedBehaviorSanitizer. Guest process
memory intentionally lives to exit. These checks do not establish gameplay FPS.
