Merge lane base check: develop 7003d2d9761d

Merge lane base check: run the full gate on `develop` at `7003d2d9761dc1dc0e10b10f3f6eb1957b527c02` 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 7003d2d9761d certified green by merge_lane.py run — full gate 604s, 55,241 passed, 0 failed (tree e7528b63). No PRs, nothing ejected. Memory: none applied.