If you're building an app on top of OpenAI or Anthropic, you've probably noticed something uncomfortable: there's no native way to limit how much any individual user can cost you. OpenAI gives you org-level spend caps and project budgets. These protect OpenAI's billing relationship with you. They don't protect you from the one user who discovers they can run your AI feature in a loop at 3am and generate $400 in API costs before you wake up. I learned this the hard way. Twice. W...