If you've shipped an AI feature on Vercel, you already know the fear: a prompt-injection loop, a misconfigured retry, or just genuine unexpected traffic, and your LLM bill stops being a line item and starts being an incident. It's not hypothetical — usage-based hosting bills spiking into five figures overnight is a well-documented enough pattern that entire blogs exist to chronicle it, Vercel included . What's changed is that Vercel now ships an actual spend cap for this specific failure mod...