Merge lane base check: develop 893f9d446e9f

Merge lane base check: run the full gate on `develop` at `893f9d446e9fc5e08bb048e5bd7a05c689abbe1c` 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 893f9d446e is red (develop_red reported). 4 mirror tests fail: comments quoting 12-digit Alembic revision ids (e.g. 202611012400, models/projects.py:187) trip the mirror's account-id detector. No PR ejected. Memory: none applied.