diff --git a/apps/ai-game-creator-shell/src-tauri/src/agent/direct_project_history.rs b/apps/ai-game-creator-shell/src-tauri/src/agent/direct_project_history.rs
index 3b67e47eb..531bf5231 100644
--- a/apps/ai-game-creator-shell/src-tauri/src/agent/direct_project_history.rs
+++ b/apps/ai-game-creator-shell/src-tauri/src/agent/direct_project_history.rs
@@ -304,7 +304,10 @@ pub(crate) fn read_direct_project_chat_history_at(
 
 #[cfg(test)]
 mod tests {
-    use super::is_direct_project_internal_context_item;
+    use super::{
+        append_direct_project_history_item_at, history_path,
+        is_direct_project_internal_context_item, read_direct_project_history_items_at,
+    };
     use serde_json::json;
 
     #[test]
@@ -351,4 +354,28 @@ mod tests {
             }]
         })));
     }
+
+    #[test]
+    fn append_repairs_truncated_tail_before_idempotency_scan() {
+        let root = tempfile::tempdir().expect("temp project");
+        crate::init_local_game_project_at(root.path(), "tail-repair", "尾行修复")
+            .expect("init project");
+        let path = history_path(root.path());
+        std::fs::create_dir_all(path.parent().expect("history parent")).expect("history dir");
+        std::fs::write(
+            &path,
+            br#"{"type":"response_item","payload":{"type":"message"}"#,
+        )
+        .expect("write truncated history tail");
+        let item = serde_json::json!({
+            "type": "message",
+            "role": "assistant",
+            "id": "tail-repair-item",
+            "content": [{"type": "output_text", "text": "已修复"}]
+        });
+        append_direct_project_history_item_at(root.path(), &item).expect("repair and append");
+        let items =
+            read_direct_project_history_items_at(root.path()).expect("read repaired history");
+        assert_eq!(items, vec![item]);
+    }
 }