Update app.py

app.py

@@ -735,7 +735,8 @@ def set_tools() -> List[Tool]:
         )
     if "Retrieval" in tool_names:
         # Get the retriever tool and save it to st.session_state.retriever_tool.
-        get_retriever()
+        if not st.session_state.retriever_tool:
+            get_retriever()
         if st.session_state.vector_store_message:
             st.write(st.session_state.vector_store_message)