digraph "" {
   radicle_node [label="Radicle node"];
   broker [label="CI broker"];
   adapter [label="Adapter"];
   engine [label="External CI system"];

   radicle_node -> broker [label="change event"];
   broker -> adapter [label="invoke"];
   adapter -> engine [label="run"];
   engine -> adapter [label="web hook?"];
   adapter -> broker [label="result"];
}