Merge lane base check: develop d0c72be900ef

Merge lane base check: run the full gate on `develop` at `d0c72be900efaf7d233f62dd85e4a3c4d381c9e0` 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 d0c72be900: develop_red. 2 tests in test_slot_two_writers.py fail deterministically — 82a2652467 (Task 11384) splatted values(**...) in slot_state.py, blinding the occupancy-family scan. Queue empty. Memory: none applied.