Merge lane base check: develop c4b0e88a4f46

Merge lane base check: run the full gate on `develop` at `c4b0e88a4f464dc725434263039aaca8265b26e3` 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: full gate green on develop c4b0e88a4f46, certified via merge_lane.py run (694s, all gate). Nothing merged or ejected; queue empty, no breaches. Memory: none applied.