Merge lane base check: develop 3eec0a8eaa41

Merge lane base check: run the full gate on `develop` at `3eec0a8eaa4187f11aacdb33aa721fd5598d1305` 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 3eec0a8 certified green by merge_lane.py run (tree d9f16ac). Run 1 red: 2 vitest tests. Run 2 on the same tree passed (57,825 tests); the lane logged a flake. Nothing merged or ejected. Memory: used mem-25266; none proposed.