feat(alert): suppress offline + add staleness alert for intermittent hosts

internal/alert/rules.go

@@ -122,6 +122,16 @@ func alertPayload(ctx context.Context, st *store.Store, ev notification.Event, a
 	}
 }
 
+// ResolveOnModeChange clears any open agent_offline and stale_schedule
+// alerts for a host whose always-on flag was just toggled. The next
+// 60s tick re-raises whichever still applies under the new mode, so
+// this is a self-correcting "wipe and let the sweep settle" call.
+// Safe to invoke from the HTTP layer (it only touches the store + hub).
+func (e *Engine) ResolveOnModeChange(ctx context.Context, hostID string, when time.Time) {
+	e.resolveAndNotify(ctx, hostID, KindAgentOffline, "", when)
+	e.resolveAndNotify(ctx, hostID, KindStaleSchedule, "", when)
+}
+
 // resolveAndNotify clears the open (or acknowledged) alert matching
 // (host_id, kind, dedup_key) via store.AutoResolve, then fires
 // alert.resolved for the row(s) actually closed. Best-effort —