Merge lane base check: develop e6b9f3f1b6a7

Merge lane base check: run the full gate on `develop` at `e6b9f3f1b6a719f69f7cb3e7b8310fb3347d752d` 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.

develop e6b9f3f1b6a7 certified: full gate green (66,498 passed, 0 failed); lane recorded event=certified. Nothing ejected, develop green. Memory: none applied.