#770 HIGH: Event await/emit race condition for infinite timeout waits

Issue #5 from audit: Race window between await_event event check and wait registration. If emit_event runs in between, event is stored but sleeping run with infinite timeout won't be woken. Events NOT lost (in e_* table), but run stays sleeping. Mitigation: Most workflows use timeouts. Fix: Re-check event table after registering wait before sleeping. Requires SQL function update. Deferred to Phase 2.