Merge lane: jaah

Merge lane run: batch the queued PRs, run the full gate (if any) once on their merged tree, and merge the batch when it is green. Filed by the control plane (`app/merge_lane.py::ensure_lane`).

Merged 5 PRs in 3 quick-gated batches (#6318, #6319, #6321, #6322, #6320); 0 ejected. develop green: the stale Vale red on 686a2b39 was re-run on 870868443 and passed. Queue empty.