Merge lane base check: develop 9ec0af9d0511

Merge lane base check: run the full gate on `develop` at `9ec0af9d0511409680e22933b2f660f7d50a545e` 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 9ec0af9d0511 red: 5 tests in test_credential_key_rotation.py failed because #7348 adds dev keys to a local-stack ring. Fixed forward in #7352 (tests pin APP_ENV=test), merged as a7099eb2ae63; deploy succeeded. Memory: none applied.