CI only: Windows deadline test waits for readiness
Merged
BA
4d ago+216+216+012345678901234567890123456789-11-11-01234567890123456789
CI-only draft for a worker's Windows proof. Not for merging; the change reaches main through the gated push.
Summary by cubic
Makes the Windows subprocess deadline tests reliable by starting the output deadline only after confirming the descendant process is actually running.
- Adds
output_until_ready, which polls a readiness predicate on Windows before starting the output deadline timer. - Updates the Windows pipe tests to wait for the descendant PID to be live instead of assuming it starts immediately.
- Adds a guarded mutation proving the deadline test fails when readiness gating is removed.