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 10 PRs (#6384-#6393) in 5 quick-gated batches, all green; 0 ejected. develop green (#6384 cleared stale mypy red); Jaah Deploy success at fab40b178. Memory: none applied.