Merge lane base check: develop 608e99ffaf6d

Merge lane base check: run the full gate on `develop` at `608e99ffaf6d0374b983c2038397b250e14d1955` 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 608e99ffaf6d certified green by merge_lane.py run: full gate exit 0 in 698s, 56521 passed / 0 failed (tree cd63c043). Nothing ejected; no fix task. Memory: none applied.