Merge lane base check: develop bf9c3b0000cc

Merge lane base check: run the full gate on `develop` at `bf9c3b0000cc066c1b2880bd6497f994ab147646` 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 bf9c3b0: merge_lane run reported develop_red (gate 2×). All 8760 tests pass; only Runner CLI lock audit fails — new high advisory GHSA-xjj6-f33q-929c (undici) in pi-coding-agent lock. Nothing merged/ejected. Memory: none applied.