Merge lane base check: develop c7b0ce8d4562

Merge lane base check: run the full gate on `develop` at `c7b0ce8d4562d0ad015b4b07fe2f4cbd3e779537` 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).

Base check develop c7b0ce8d4: RED, reported develop_red via merge_lane.py run (full gate 3×). 1/55056 failed: test_plan_matrix[business-trial] runner_slots None≠3; passes in isolation → order-dependent leak. Nothing merged/ejected. Memory: none applied.