Index host operations by kind to avoid polling history scans

src/lib/server/hosts/schema.ts

@@ -29,6 +29,10 @@ export function ensureHostSchema(handle: Database.Database): void {
             UNIQUE(host_id, idempotency_key)
         );
         CREATE INDEX IF NOT EXISTS ec_host_operations_queue ON ec_host_operations(host_id, state, created_at);
+        -- Polling checks cancellations and preparation by kind across retained
+        -- 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 TABLE IF NOT EXISTS ec_host_operation_events (
             id INTEGER PRIMARY KEY AUTOINCREMENT, operation_id TEXT NOT NULL REFERENCES ec_host_operations(id),
             state TEXT NOT NULL, created_at TEXT NOT NULL, error TEXT