Fix red develop 459eb1abc7fe

The merge lane found `develop` red at `459eb1abc7fe14142346a2c49afeb5c26ab70ded` 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/token_billing/test_outbox.py::test_the_effect_runs_on_dbos_only_when_its_transaction_commits_and_a_failure_is_retried` - `api-unit-dc-test` The whole gate log: artifact `15649` on lane task 13630. 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.

Fixed red develop: DBOS's CONCURRENTLY migration hung on a connection an earlier test leaked idle in a transaction; launch() now ends those first, and the timeout dump reaches the log. 3 full API runs green, 0 worker deaths. PR #7938 queued. Follow-up draft 13650. Memory: proposed 1 gotcha.