Avoid scanning operation history on agent polls

src/lib/server/hosts/index.ts

@@ -522,11 +522,14 @@ export function pendingHostOperationRows(hostId: string, lane: OperationLane = '
             .all(hostId, Number(host.readiness === 'ready' || host.mode === 'draining'), Number(host.inventory.capabilities?.includes('instance.cancel-create') ?? false),
                 ...(lane === 'health' ? [new Date(Date.now() - 30_000).toISOString()] : [])) as OperationDeliveryRow[];
         const preparationLimit = fleetSettings().preparationConcurrency;
-        const preparing = new Set((database().prepare(`SELECT DISTINCT host_id FROM ec_host_operations
-            WHERE kind IN ('library.download','library.import') AND last_delivered_at IS NOT NULL
-            AND state IN ('pending','accepted','running','unknown')`).all() as { host_id: string }[]).map(row => row.host_id));
+        const libraryKinds = ['library.download','library.import'];
+        const preparing = preparationLimit && rows.some(operation => libraryKinds.includes(operation.kind))
+            ? new Set((database().prepare(`SELECT DISTINCT host_id FROM ec_host_operations
+                WHERE kind IN ('library.download','library.import') AND last_delivered_at IS NOT NULL
+                AND state IN ('pending','accepted','running','unknown')`).all() as { host_id: string }[]).map(row => row.host_id))
+            : new Set<string>();
         const admitted = rows.filter(operation => {
-            if (!['library.download','library.import'].includes(operation.kind) || preparing.has(hostId) || !preparationLimit) return true;
+            if (!libraryKinds.includes(operation.kind) || preparing.has(hostId) || !preparationLimit) return true;
             if (preparing.size >= preparationLimit) return false;
             preparing.add(hostId); return true;
         });

src/lib/server/hosts/schema.ts

@@ -43,6 +43,7 @@ export function ensureHostSchema(handle: Database.Database): void {
         -- history. The queue index cannot narrow those lookups beyond host_id,
         -- causing a history scan for every queued command on Node's main thread.
         CREATE INDEX IF NOT EXISTS ec_host_operations_kind ON ec_host_operations(host_id, kind, created_at);
+        CREATE INDEX IF NOT EXISTS ec_host_operations_kind_state ON ec_host_operations(kind, state);
         CREATE TABLE IF NOT EXISTS ec_host_operation_payloads (
             operation_id TEXT PRIMARY KEY REFERENCES ec_host_operations(id) ON DELETE CASCADE,
             payload TEXT NOT NULL