Merge lane base check: develop c1d936c13323

Merge lane base check: run the full gate on `develop` at `c1d936c1332302eda017e7030e5f5f7d6d5b017a` 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: develop c1d936c13323 certified green. Full gate passed on its 3rd run (57,748 passed); run 1 had 40 API-unit failures, recorded as flakes. Queue empty. Nothing merged or ejected. Memory: used mem-25266; proposed none.