fix

codex-rs/core/src/codex.rs

@@ -4035,6 +4035,9 @@ impl Session {
         let mut active = self.active_turn.lock().await;
         match active.as_mut() {
             Some(at) => {
+                if at.tasks.is_empty() {
+                    return Err(input);
+                }
                 let mut ts = at.turn_state.lock().await;
                 for item in input {
                     ts.push_pending_input(item);

codex-rs/core/src/codex_tests.rs

@@ -4783,6 +4783,25 @@ async fn queued_response_items_for_next_turn_move_into_next_active_turn() {
     assert_eq!(sess.get_pending_input().await, vec![queued_item]);
 }
 
+#[tokio::test]
+async fn inject_response_items_rejects_pending_turn_start_reservation() {
+    let (sess, _tc, _rx) = make_session_and_context_with_rx().await;
+    *sess.active_turn.lock().await = Some(ActiveTurn::default());
+    let pending_item = ResponseInputItem::Message {
+        role: "user".to_string(),
+        content: vec![ContentItem::InputText {
+            text: "queued during turn-complete".to_string(),
+        }],
+    };
+
+    let err = sess
+        .inject_response_items(vec![pending_item.clone()])
+        .await
+        .expect_err("empty active turn reservation should reject injected items");
+
+    assert_eq!(err, vec![pending_item]);
+}
+
 #[tokio::test]
 async fn on_task_finished_records_queue_only_mailbox_mail_without_restart() {
     let (sess, tc, _rx) = make_session_and_context_with_rx().await;