Grafana 13 externalised its core data sources; nixpkgs no longer bundles the Elasticsearch datasource, so every DMARC panel failed with "Plugin not registered". Load the official Grafana-signed elasticsearch plugin via declarativePlugins, pin the dmarc-ag/dmarc-fo datasource UIDs (Grafana 11+ resolves datasource template variables by UID, not name), and clear stale uid-less records left by an earlier deploy.