Process-wide serial lock around the socket-binding and PTY-spawning
integration tests in spaceshd. Running several at once on a many-core
box starved each other's async tasks and tripped timing assumptions,
causing ~1/10 flakes under cargo test --workspace. Unit tests stay
parallel. 0/20 spaceshd + 0/5 workspace runs after the change.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
vasyansk
