Technical recruiter screen: duplicate requests and a streaming chat UI

The first recruiter call is more technical than most. After the background questions (how much of the last year you spent writing code, whether you lean frontend, backend or full stack, and the languages and frameworks you use every day), expect short design and fundamentals questions:

1. How do you make sure the same request is never processed twice?
2. How would you build a chat UI that streams model replies reliably?
3. A chatbot backend gets a flood of messages: what fails first, and if the bot system goes down, how do you bring it back to its earlier state?
4. Front-end basics, for example how JavaScript handles threads and the difference between useState and useRef in React.

Short, concrete answers that name the mechanism (idempotency keys, retries, state recovery) land best.