Merge lane base check: develop 4c879c4e17c7

Merge lane base check: run the full gate on `develop` at `4c879c4e17c77bedcd589e2d4edaad3228cee1bb` 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 (Task 6722).

Base check certified: develop 4c879c4e17c7 full gate green (884s, 57994 passed, 0 failed) via merge_lane.py run; event=certified reported. No rows queued, nothing ejected; develop green. Memory: used mem-25266; none proposed.