hive-agent: run the event store in WAL and give turn-stats writes a busy timeout

docs/agent-lifecycle/persistence.md

@@ -92,6 +92,10 @@ One table:
 - `events(id, ts, kind, payload_json)` — every `LiveEvent` the
   harness emits during turn loop execution.
 
+The db runs in WAL mode, so `-wal` and `-shm` files sit beside it while
+the harness is up. Copy or back up the three together, or the recent rows
+sit in the `-wal` file until a checkpoint.
+
 <!-- vale write-good.Passive = NO -->
 The harness both writes and vacuums it. Cleanup runs in-container
 because hive-c0re runs as the unprivileged `hive-core` user under