HarborCart promises an internal checkout-success objective. Feature launches should slow when reliability consumes the agreed allowance. Which operational mechanism best connects releases to that objective?

1. A CPU quota used as the checkout-success objective.
2. A requirement that every incident be attributed to one person before releases resume.
3. An error-budget policy tied to a measured checkout-success SLI and SLO.
4. A release calendar based only on developer availability.