Merge lane base check: develop 902ea0c59059

Merge lane base check: run the full gate on `develop` at `902ea0c59059924b989afeb188bc017fe1c6ca5b` 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).

develop 902ea0c59059 certified green: merge_lane.py run full gate passed in 665s (56637 tests, 0 failed); event=certified tree 19e9b7c0. Nothing merged or ejected. Memory: none applied.