Merge lane base check: develop 1597a850bb16

Merge lane base check: run the full gate on `develop` at `1597a850bb16dd8e720806071dfd9eb9ebec536e` 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.

develop 1597a850bb16 RED (reported develop_red): Deb upgrade stage — test_deb_upgrade.py build_deb doesn't expand ${JAAH_PYTHON_FLOOR} added to packaging/nfpm.yaml by PR #7279 (Task 11108); 9 errors, all else green. Memory: none applied.