events: persist to sqlite, survive harness restart

hive_ag3nt::events::Bus replaces its in-memory VecDeque with a sqlite-
backed store at /state/hyperhive-events.sqlite (overridable via
HYPERHIVE_EVENTS_DB). emit() inserts a row; history() reads back the
most recent 2000 events. survives harness restart now — operator reload
mid-investigation no longer wipes the trail.

vacuum runs hourly (immediate first sweep): drop rows older than 7
days, then trim to 2000 newest. two-stage so a quiet agent keeps a
useful tail and a chatty one stays bounded. wired into both
hive-ag3nt and hive-m1nd via spawn_events_vacuum.

if the db open fails (e.g. no /state mount in dev), Bus runs in
no-store mode — events still broadcast, just nothing persisted.

hive-ag3nt/src/bin/hive-m1nd.rs

@@ -61,6 +61,7 @@ async fn main() -> Result<()> {
             let login_state = Arc::new(Mutex::new(initial));
             let ui_state = login_state.clone();
             let bus = Bus::new();
+            spawn_events_vacuum(bus.clone());
             let ui_bus = bus.clone();
             let ui_socket = cli.socket.clone();
             tokio::spawn(async move {
@@ -89,6 +90,22 @@ async fn main() -> Result<()> {
     }
 }
 
+/// Vacuum events older than 7 days, cap to 2000 most-recent rows.
+fn spawn_events_vacuum(bus: Bus) {
+    tokio::spawn(async move {
+        let interval_secs = 3600u64;
+        let keep_secs: i64 = 7 * 24 * 3600;
+        let keep_rows = 2000;
+        loop {
+            let n = bus.vacuum(keep_secs, keep_rows);
+            if n > 0 {
+                tracing::info!(removed = n, "events vacuum");
+            }
+            tokio::time::sleep(Duration::from_secs(interval_secs)).await;
+        }
+    });
+}
+
 async fn serve(socket: &Path, interval: Duration, bus: Bus) -> Result<()> {
     tracing::info!(socket = %socket.display(), "hive-m1nd serve");
     let mcp_config = turn::write_mcp_config(socket).await?;