Merge lane base check: develop 58445d2ed7b0

Merge lane base check: run the full gate on `develop` at `58445d2ed7b05f5f998f5d65a0680ffb46e3b170` 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.

Base check on develop 58445d2ed7b0 is red (develop_red reported). The full gate ran 3 times. Each red run was an xdist worker crash in the API unit suite, on a different test each time. The focused rerun passed, so this looks like a flaky crash. Memory: none applied