Merge lane base check: develop 6e8fe9921790

Merge lane base check: run the full gate on `develop` at `6e8fe9921790008b8be0e597eafe4c3bbcc8eeab` 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 6e8fe9921790 RED (develop_red reported by merge_lane.py run): jaahd test_host_platform_guard — runner_cli_pins.py 6×fcntl vs frozen 4 (from 2ecdd83a2, Task 8810); reproduced focused. No PR. Memory: used mem-22518.