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 PR #6667 (task 9116) into develop as 2200ca00c after the quick gate passed on the merged tree (6003 tests). Nothing ejected. The quick gate is green on the develop head, mypy included; the develop_red flag pointed at the older commit 86fb5954 and is stale. Queue empty. Batch time 51s (gate 31s, merge 8s). Memory: none applied.