Merge lane base check: develop 7851c60c832f

Merge lane base check: run the full gate on `develop` at `7851c60c832f088c71b9ffe6f08ccf77c777fd87` 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 7851c60c: develop_red reported by merge_lane.py run. Only stage red: Runner CLI lock audit hung twice (1201s/279s). The same audit run straight passed in 2s, so likely an npm registry hang, not code. No PRs queued. Memory: proposed 1 gotcha (mem-23540).