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 #6136 (86e2914) and #6127 (d8e264e), each quick-gated green (5848 passed). Ejected #6138: merge conflict with develop (dirty). Stale develop-red record for c2ad861 re-checked on the new head: Vale and ast-grep pin both pass. develop green.