Actual self-probe island
This command closes its own stdout in the actual gate position. Re-closing it would test the harness, so the checker must exclude it explicitly and return 3 because nothing else ran.
enforced: closed-stream-check.py reports one own-probe, zero probes, and exit 3.advisory: nothing else here is real.
python3 -c "import sys; sys.exit(0)" 1>&- # exit 0