The macOS CI job failed ``test_lock_blocks_concurrent_access`` because
``fcntl.flock`` on BSD/macOS is per-*process*, not per-FD: two threads
in the same process both acquire even when they open their own file
descriptors. The test passed on Linux (per-FD flock) and Windows
(per-FD ``msvcrt.locking``) but was never actually exercising the
lock's real contract.
``mine_lock`` is designed to serialize multi-*agent* access — i.e.,
separate processes, not threads. Switch the test to
``multiprocessing.get_context('spawn')`` with a module-level worker
(so the spawn pickles cleanly) so it:
1. reflects the actual use case (one lock per mining process);
2. passes on all three OSes without flock-semantics branching;
3. catches real regressions (a broken lock would now let both
processes through, exactly what we care about).
Hold time bumped to 0.3s and the "wait until p1 acquires" delay to
0.2s to tolerate spawn's higher startup latency on macOS/Windows.
Igor Lins e Silva
e052074624