diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index fcd274841a..d898f2c97f 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -3381,6 +3381,9 @@ impl Session {
             );
             state.replace_history(items.clone(), reference_context_item.clone());
         }
+        // `items` may have gained a concurrent ghost snapshot tail under the
+        // state lock, so refresh the persisted replacement history to match the
+        // in-memory install.
         compacted_item.replacement_history = Some(items);
 
         self.persist_rollout_items(&[RolloutItem::Compacted(compacted_item)])