Add more comments to track_newly_created_chains.

linera-core/src/chain_worker/state/mod.rs

@@ -380,15 +380,19 @@ where
         self.recent_blobs.insert(blob).await
     }
 
-    /// Adds any newly created chains to the set of `tracked_chains`.
+    /// Adds any newly created chains to the set of `tracked_chains`, if the parent chain is
+    /// also tracked.
+    ///
+    /// Chains that are not tracked are usually processed only because they sent some message
+    /// to one of the tracked chains. In most use cases, their children won't be of interest.
     fn track_newly_created_chains(&self, executed_block: &ExecutedBlock) {
         if let Some(tracked_chains) = self.tracked_chains.as_ref() {
             if !tracked_chains
                 .read()
                 .expect("Panics should not happen while holding a lock to `tracked_chains`")
                 .contains(&executed_block.block.chain_id)
             {
-                return;
+                return; // The parent chain is not tracked; don't track the child.
             }
             let messages = executed_block.messages().iter().flatten();
             let open_chain_message_indices =