fix: true atomic bulk topology -- apply_set_parent + single write, add # Errors docs

hive-c0re/src/coordinator.rs

@@ -719,7 +719,12 @@ impl Coordinator {
     /// Batch version of [`reparent_with_notify`]: applies all moves under a
     /// single `META_LOCK` acquisition (one git commit) then sends per-agent
     /// notifications for each move that actually changed topology.
-    /// First validation failure aborts the whole batch.
+    /// First validation failure aborts the whole batch with no disk writes.
+    ///
+    /// # Errors
+    ///
+    /// Propagates any error returned by [`crate::meta::bulk_commit_topology`]
+    /// (validation failure or topology-file write error).
     pub async fn reparent_bulk_with_notify(
         self: &Arc<Self>,
         moves: &[(&str, Option<&str>)],