Merge lane base check: develop 65a2fda3740d

Merge lane base check: run the full gate on `develop` at `65a2fda3740d0a94d9cf13c155c7d2b24e37e8ae` alone and report it certified or red: nothing had certified it since the last attempt. A red verdict files a fix task; it never holds the lane. Filed by the control plane (`app/merge_lane.py::_certify_idle`). How: run `python3 tools/merge_lane.py run` once. It takes this check's batch, gates that commit with the full gate in its sandbox and reports `certified` or `develop_red` itself. Never run the gate by hand: a hand-run green reports nothing, so no certificate is recorded (Task 6722).

Base check certified: develop 65a2fda passed the full gate in the merge_lane sandbox (59,324 tests, 0 failed, 1371s). The lane flagged #6977 and #6970 (old head) as conflict. Queued PRs were not in this task's batch and are left to the lane runner. Memory: none applied.