Merge lane base check: develop 64d7239f93de

Merge lane base check: run the full gate on `develop` at `64d7239f93ded83b5f0052d64bb98994a9920e04` 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 64d7239f93de certified green (full gate 3×: one Jaahd unit failure recorded as flake, final run 57,858 passed / 0 failed). Nothing merged or ejected. Deferred: flake test id not logged; Stop hook printed a credential-shaped value.