I'm currently developing a web application with a backend in Python using FastAPI, and I'll be deploying it to AWS Lambda and using AWS DynamoDB as the database. The frontend will be built using ReactJS in the future. I need help implementing a functionality where certain endpoints can only be accessed conditionally, based on a previous call.

Detailed Requirements

• A user can navigate to a specific question.
• The user can call the get_explanation endpoint for this specific question.
• Once the user receives the explanation, they can enter a follow-up question in a text input box.
• This input text will be sent to a follow_up_question endpoint, where the user can ask a follow-up question about the explanation.
• After the user gets a response to the follow-up question, the input text box should become unusable. The user can only ask one follow-up question after getting the explanation.

My Questions

• What are the most efficient ways of designing the backend so that the follow_up_question endpoint can only be called if the get_explanation endpoint has already been called for the same question item?
• How can I ensure that once the follow_up_question endpoint has been called for that question, it can't be called again?
• How should I handle this logic on the frontend using ReactJS to ensure a smooth user experience?
• Some of you may suggest using the database to track state, but is this really the most efficient way?