Last year a developer watched an agent burn $700+ in 72 hours. No budget control, no kill switch — just a loop and a credit card. It is a common story in agent-builder communities, and the response is almost always the same: buy a better dashboard.
Dashboards will not save you. Visibility without enforcement just shows you the number while it grows. What actually works is governance: four controls, the cheapest of which costs $0.
1. Ceiling per plan, not per account¶
Give every unit of work — the nightly scrape, the support shift, the migration job — its own cost ceiling and an expiry date. Per plan, never per account: one looping task should never be able to eat the budget for everything else. A workload with no end date is a subscription you forgot you bought.
2. Fail closed, never warn¶
When the ceiling is hit, the action gets blocked, recorded as blocked, and never retried automatically. A warning is just an invitation for the loop to finish. Alerts at 50%/80% are information; the block is the control.
3. Meter for free¶
If your framework has no native budget controls, put it behind a meter. Helicone's free tier covers 10k requests/month; LangWatch's free tier covers 200k events/month. Then confirm the meter's counts reconcile against your actual provider bill — the meter is the watchdog, the bill is the truth.
4. Replay your worst incident in a sandbox¶
Run the exact loop scenario that burned you and confirm it terminates at its plan ceiling before it touches real money. Acceptance test: the loop exhausts its own plan and stops.
The takeaway¶
Warnings decay into ignored banners. Blocks hold. These four steps — plan-bound ceilings, fail-closed blocks, free metering, and a sandbox replay — are the core of a spend-control policy that turns a catastrophic "oops" into a recorded, contained event. The copy-paste templates for the spend-limit policy, the plan-bound schema, and the audit-row format live in the Studio Edition playbook — the four steps above are the whole system, the templates just save you typing.