Windows CI was red on f460cd5: the patch_flock fixture patched presence.fcntl,
which only exists on POSIX (msvcrt on win32), erroring all 16 presence-test
setups. Now patches the platform-agnostic _presence_lock context manager
(-> nullcontext per call) and skips the inherently-POSIX flock-acquire test on
win32. Dormant prod code unchanged.
705 tests pass, seedgo 100%. Fix by @hooks.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GFihce1oLtp6UDAPGryYSv