Merge lane base check: develop a743663845ed

Merge lane base check: run the full gate on `develop` at `a743663845edbb40d7b048a4bf4e3d032ca7004d` 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.

develop a743663845 red: launch_memory.py:5 cites 'Task 11539', failing 3 mirror-sensitive stages. Fix-forward PR #7423 queued in merge lane (focused suites 95 passed). Memory: none applied.