topology: drop manager-root special case + notify three agents on reparent (#743)

hive-c0re/src/dashboard.rs

@@ -2188,16 +2188,21 @@ async fn post_set_parent(
         .map(str::trim)
         .filter(|s| !s.is_empty())
         .map(str::to_owned);
-    match crate::topology::set_parent(&child, new_parent.as_deref()) {
+    // `reparent_with_notify` wraps `topology::set_parent` with the
+    // three notification messages (#743) + the ContainerView rescan.
+    // Idempotent same-parent calls skip both the messages and the
+    // disk write per the topology fast-path.
+    match state
+        .coord
+        .reparent_with_notify(&child, new_parent.as_deref())
+        .await
+    {
         Ok(()) => {
             tracing::info!(
                 child = %child,
                 new_parent = ?new_parent,
                 "operator: set-parent via dashboard"
             );
-            // Topology drives ContainerView.parent; refresh the
-            // snapshot so connected viewers see the new tree.
-            state.coord.rescan_containers_and_emit().await;
             (StatusCode::OK, "ok").into_response()
         }
         Err(e) => error_response(&format!("set-parent {child} failed: {e}")),