Merge lane base check: develop 446bdd74ca06

Merge lane base check: run the full gate on `develop` at `446bdd74ca0677dfb92159ebb68405f1c6915441` 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 446bdd74ca06 is red: the full gate had 2 API unit (./dc test) failures that failed again on a focused rerun. merge_lane.py reported develop_red, which files a fix task. Nothing was ejected and no PR was opened.