Merge lane base check: develop d1af53993e01

Merge lane base check: run the full gate on `develop` at `d1af53993e01f465ac31955ab16306e137dfb8ec` alone and report it certified or red: nothing had certified it since the last attempt. A red verdict files a fix task; it never holds the lane. Filed by the control plane (`app/merge_lane.py::_certify_idle`). How: run `python3 tools/merge_lane.py run` once. It takes this check's batch, gates that commit with the full gate in its sandbox and reports `certified` or `develop_red` itself. Never run the gate by hand: a hand-run green reports nothing, so no certificate is recorded.

develop d1af53993e01 RED on full gate (66381 pass, 1 fail): tests/test_live_cast_engine.py::test_a_run_killed_mid_way_resumes_after_restart_and_pays_each_item_once; develop_red reported by merge_lane.py run. No PRs queued.