The advisory flock in run_checks.py uses one system-wide lock path
(~/.cache/coyote/review-stack.lock). Concurrent runs of the timeout/deadline
tests contend on it: the losers sleep in the bounded retry loop, the total
deadline (computed before lock acquisition) expires, and commands record
'skipped: deadline' instead of the expected timeout/kill behavior.
- run_checks.py: ADVERSARY_STACK_LOCK_PATH env override relocates the lock
file (isolation seam, documented alongside the other env seams); every
other lock semantic (default path, bounded wait, proceed-unlocked warning,
fd held for process lifetime, skip when no commands) is unchanged.
- run_checks.py: guard the POSIX-only fcntl import — windows-latest CI has
python3 and runs these tests, so the unconditional import crashed the
script there; on non-POSIX the lock is now skipped with a stderr WARN,
matching the script's documented non-POSIX limitations.
- tests: the shared adversary_script_command helper points every spawned
script at its own throwaway lock path, isolating the run_checks tests from
each other and from any real review running on the same machine.
- tests: adversary_run_checks_stack_lock_path_is_env_overridable pins the
override (lock file appears at the overridden path across two sequential
runs; no lock file is created when no commands are declared).
Dark-Alex-17
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