I built an AI chat over my CV on a zero-pound inference budget

My CV is a PDF, and PDFs do not answer questions. So I built ask.hiten.dev : a streaming chat grounded in my actual career history, where a recruiter can ask "why should I hire you over another senior frontend engineer?" and get a real answer. The constraint that made it interesting: the total inference budget is zero. No OpenAI bill, no hosted vector DB, nothing. Here is what that actually took. Four free providers and a failover chain No single free tier is reliable enough to put in front of strangers. Groq's free tier caps at 100k tokens/day, and I hit that cap on day one. OpenRouter's free models come and go. Cerebras occasionally queues you out at busy times. The fix is boring and effective: an ordered provider chain, all OpenAI-compatible, walked per-request until one answers. Groq (llama-3.3-70b) -> OpenRouter (gpt-oss-120b:free) -> NVIDIA (llama-3.3-70b) -> Cerebras (gpt-oss-120b) Each provider is just a base URL, a key and a model name. The API route tries each in order; the first 2xx with a body wins, and the response streams straight through. The client gets an X-Provider header so I can see who served what in the logs. Two details that mattered: Empty env vars are not unset. Docker Compose's ${VAR:-} yields an empty string, which defeats ?? defaults in Node. Every key goes through a helper that coerces "" to undefined , otherwise a provider with no key "exists" and fails every request. You cannot cheaply probe a token-per-day cap. My health check hits GET /models on each provider (auth check, 60s cache). It tells you "key works, service up", not "you have tokens left". The failover chain covers the gap: a TPD-capped provider fails fast and the next one picks up. If every provider is down, the page itself says so. The health check runs server-side at render time, and instead of a broken chat you get a short maintenance note. Never ship a chat UI that can fail after the user has typed. Open-weight models do not follow formatting orders My site's voice avoi