Reconcile host preparation on heartbeats instead of polls

src/lib/server/hosts/preparation.ts

@@ -173,7 +173,7 @@ function supersedeUndeliveredDownloads(hostId: string): void {
     }
 }
 
-/** Agent heartbeats and polls drive durable preparation; no open UI or in-memory worker is needed. */
+/** Heartbeats drive durable preparation; idle checks do not reserve the SQLite writer. */
 export function reconcileHostPreparation(hostId: string): HostPreparation {
     return db().transaction(() => {
         const host = getHost(hostId);
@@ -203,5 +203,5 @@ export function reconcileHostPreparation(hostId: string): HostPreparation {
             scheduleAvailabilityRefresh();
         }
         return status;
-    }).immediate();
+    })();
 }