Implement authorized landmark roaming (#130)

crates/metacrate-grid-agent/src/backend.rs

@@ -187,6 +187,14 @@ impl LibremetaverseClientOwner {
         &self.client
     }
 
+    /// Returns the one native agent manager owned by this composition root.
+    /// `MetaCrate` adapters clone the `Arc`; they never construct a parallel
+    /// compatibility manager graph.
+    #[must_use]
+    pub fn agent(&self) -> Arc<libremetaverse::AgentManager> {
+        Arc::clone(&self.agent)
+    }
+
     /// Creates the supervised live-session adapter without logging in.
     ///
     /// # Errors