Stop Your OpenAI Bill from Exploding: Per-User LLM Budget Caps in Node.js

The cost incident that started this Three weeks after we put our chatbot into production, I opened the OpenAI billing dashboard on a Monday morning and stopped breathing for a second. One session — not one user, one session — had burned through roughly four times the daily budget for the entire app. Over a single afternoon. The session wasn't malicious. It was a test account someone forgot to log out of, hammering the chat endpoint in the background while reloading a broken page. No rate limit w