Merge lane base check: develop 3f58da0bb10e

Merge lane base check: run the full gate on `develop` at `3f58da0bb10e9d4314b0bfd56aeb736902d4aa43` 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 certified: full gate green on develop 3f58da0bb10e (670s, 57,859 tests, 0 failed; tree 9021c5816b80). Nothing merged or ejected; queue empty, develop green. Memory: none applied.