Merge lane base check: develop 49d0c4512ffa

Merge lane base check: run the full gate on `develop` at `49d0c4512ffa9bc69ee16adbda36c6d4740b17c4` 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 49d0c4512ffa: develop_red recorded via merge_lane.py run. Full gate 57894 passed, 1 failed (3/3 runs): test_dispatch_compose_merge_lane.py::test_every_lane_fragment_still_matches_authored_text, a lane fragment no longer in authored text. Nothing merged. Memory: none applied.