Fix red develop 113abbda8ca9

The merge lane found `develop` red at `113abbda8ca9552e7f5a4622514955f6604e563d` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_durable_enqueue_engine.py::test_the_same_workflow_id_enqueued_twice_through_the_seam_attaches_to_one_workflow` - `tests/test_live_cast_engine.py::test_a_run_killed_mid_way_resumes_after_restart_and_pays_each_item_once` - `tests/test_live_cast_engine.py::test_a_second_enqueue_while_one_is_in_flight_is_refused_and_the_publish_still_commits` - `api-unit-dc-test` The whole gate log: artifact `15687` on lane task 13652. Make `develop` pass its full gate again. Open a PR as usual: the merge lane merges a PR that fixes some of these and adds no failure even while `develop` is red.

The three DBOS engine crashes were leaked idle transactions blocking the CONCURRENTLY migration. #7938 fixed nvs.launch; this PR also ends them before the live-cast child process launches DBOS. Affected suites: 28/28 pass, quick gate green. PR #7939 queued in the merge lane.