broker: resolve <parent> sentinel to topology parent at send time (#692)

hive-c0re/src/agent_server.rs

@@ -328,9 +328,14 @@ fn handle_send(
             }
         };
     }
+    // Resolve magic-recipient sentinels (currently `<parent>`) against
+    // topology.json; no-op for ordinary names. Lets agents address
+    // structural roles without learning the label — runtime reparenting
+    // (#486) propagates for free (#692).
+    let resolved = crate::topology::resolve_recipient(agent, to);
     match coord.broker.send(&Message {
         from: agent.to_owned(),
-        to: to.to_owned(),
+        to: resolved,
         body: body.to_owned(),
         in_reply_to,
     }) {