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 #6529 (8718) and #6530 (8702); quick gate on merged tree green with 5,899 tests (batch 49s, gate 29s). None ejected. The stale red on c7b0ce8 (test_plan_matrix business-trial) passed in a focused full-gate run on new develop, so develop is green. Memory: none applied.