add optional in_reply_to field on send for conversation threading

hive-ag3nt/src/bin/hive-ag3nt.rs

@@ -378,6 +378,7 @@ async fn notify_manager_of_failure(socket: &Path, label: &str, err: &anyhow::Err
         &AgentRequest::Send {
             to: "manager".into(),
             body,
+            in_reply_to: None,
         },
     )
     .await;