Merge lane base check: develop 3e6be7706080

Merge lane base check: run the full gate on `develop` at `3e6be7706080aa76146dab74b6e95b7f7faccd86` 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 3e6be77: RED (2×, deterministic). The only failure is test_groups_api.py::test_a_rejected_create_is_recorded_with_its_refusing_status:659, still expecting response=None after 4db455f96 (Task 9135) began storing {"detail": ...} on 4xx. The fix is test-only. Memory: none applied.