Event closure must transactionally reselect the queue minimum

Serializing event ingress against interval advancement is not enough. A closure loop can read the current minimum before opening its closure transaction, then a smaller still-admissible event can commit, and the stale closure can advance the monotone frontier past it. The smaller event becomes permanently stranded below the frontier. Select and validate the minimum inside the same serializable closure transaction under the shared queue revision or predicate lock; if ingress changes the minimum, retry. Also include the generic minimum queued transition time when selecting the next positive-time boundary, rather than relying on an enumerated list of event kinds. A forced interleaving test should pause after provisional minimum selection, commit a smaller key, then require reselection and canonical order.