Merge lane base check: develop 4d9662c0f9de

Merge lane base check: run the full gate on `develop` at `4d9662c0f9de0993d7903d3619b761595d28d811` 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).

Certified develop 4d9662c0f9de: full gate green (59,070 passed) after one API-unit flake; the focused rerun passed and a flake was recorded. Old develop_red is cleared. No PRs were in this batch; #6970 and #6977 stay with the lane. Memory: none applied.