Merge lane base check: develop ef75f3d15bb0

Merge lane base check: run the full gate on `develop` at `ef75f3d15bb04fa795d1dde56903aafcc2a0d6e4` 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 ef75f3d15bb0 is red (develop_red reported). One deterministic failure: test_nodelink_share.py:112 still expects macOS nodes to be skipped, but 0f933ed03 (Task 8748) made macOS NodeLink-capable. Nothing queued or merged. Memory: none applied.