diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 8f53890e8d..e11517757e 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -3134,8 +3134,11 @@ mod handlers {
             state.set_turn_context_history(updated_turn_context_history);
             let mut applied = false;
             if state.turn_context_history.len() == user_turns
-                && let Some(turn_context) = state.last_turn_context()
-                && let Some(collaboration_mode) = turn_context.collaboration_mode.clone()
+                && let Some(collaboration_mode) = state
+                    .turn_context_history
+                    .last()
+                    .and_then(|turn_context| turn_context.as_ref())
+                    .and_then(|turn_context| turn_context.collaboration_mode.clone())
             {
                 state.session_configuration.collaboration_mode = collaboration_mode;
                 applied = true;
@@ -5143,6 +5146,76 @@ mod tests {
         assert!(update_items.contains(&expected_item));
     }
 
+    #[tokio::test]
+    async fn thread_rollback_ignores_stale_turn_context() {
+        let (sess, tc, rx) = make_session_and_context_with_rx().await;
+
+        let initial_context = sess.build_initial_context(tc.as_ref()).await;
+        sess.record_into_history(&initial_context, tc.as_ref())
+            .await;
+
+        let base_mode = sess.current_collaboration_mode().await;
+        let plan_mode = CollaborationMode {
+            mode: ModeKind::Plan,
+            settings: base_mode.settings.clone(),
+        };
+        let code_mode = CollaborationMode {
+            mode: ModeKind::Code,
+            settings: base_mode.settings.clone(),
+        };
+
+        {
+            let mut state = sess.state.lock().await;
+            state.session_configuration.collaboration_mode = plan_mode.clone();
+        }
+        let input1 = vec![UserInput::Text {
+            text: "turn 1".to_string(),
+            text_elements: Vec::new(),
+        }];
+        let response_item1: ResponseItem = ResponseInputItem::from(input1.clone()).into();
+        sess.record_user_prompt_and_emit_turn_item(tc.as_ref(), &input1, response_item1)
+            .await;
+
+        let turn_2 = vec![ResponseItem::Message {
+            id: None,
+            role: "user".to_string(),
+            content: vec![ContentItem::InputText {
+                text: "turn 2".to_string(),
+            }],
+            end_turn: None,
+        }];
+        sess.record_into_history(&turn_2, tc.as_ref()).await;
+
+        {
+            let mut state = sess.state.lock().await;
+            state.session_configuration.collaboration_mode = code_mode.clone();
+        }
+        let input3 = vec![UserInput::Text {
+            text: "turn 3".to_string(),
+            text_elements: Vec::new(),
+        }];
+        let response_item3: ResponseItem = ResponseInputItem::from(input3.clone()).into();
+        sess.record_user_prompt_and_emit_turn_item(tc.as_ref(), &input3, response_item3)
+            .await;
+
+        handlers::thread_rollback(&sess, "sub-1".to_string(), 1).await;
+        let rollback_event = wait_for_thread_rolled_back(&rx).await;
+        pretty_assertions::assert_eq!(rollback_event.num_turns, 1);
+
+        let (collaboration_mode, force_collaboration_instructions) = {
+            let mut state = sess.state.lock().await;
+            let force = state.force_collaboration_instructions;
+            state.force_collaboration_instructions = false;
+            (
+                state.session_configuration.collaboration_mode.clone(),
+                force,
+            )
+        };
+
+        pretty_assertions::assert_eq!(collaboration_mode, code_mode);
+        assert!(force_collaboration_instructions);
+    }
+
     #[tokio::test]
     async fn thread_rollback_clears_history_when_num_turns_exceeds_existing_turns() {
         let (sess, tc, rx) = make_session_and_context_with_rx().await;
diff --git a/codex-rs/core/src/state/session.rs b/codex-rs/core/src/state/session.rs
index fee67b5aff..2b47cbbe92 100644
--- a/codex-rs/core/src/state/session.rs
+++ b/codex-rs/core/src/state/session.rs
@@ -87,13 +87,6 @@ impl SessionState {
         }
     }
 
-    pub(crate) fn last_turn_context(&self) -> Option<&TurnContextItem> {
-        self.turn_context_history
-            .iter()
-            .rev()
-            .find_map(Option::as_ref)
-    }
-
     pub(crate) fn set_turn_context_history(
         &mut self,
         turn_context_history: Vec<Option<TurnContextItem>>,