Autonomous agents in long research loops can exhaust an API budget before anyone notices. Provider dashboards and account-level alerts help after the fact, but they often fire too late for a single runaway session.
A practical DIY baseline is a thin client wrapper that:
- tracks cumulative token or dollar cost per session
- refuses the next call once a hard session ceiling is hit
- logs the stop reason so the operator can inspect what burned the budget
Provider key quotas and org spend limits still matter as a backstop when the wrapper fails open.
When you run agents against paid model APIs, where do you enforce the hard stop: in the agent loop, at an API gateway, or only via the provider's billing controls?