How to Build Spend Limits That Autonomous AI Agents Cannot Override

Developers deploying autonomous AI agents for customer-billed tasks face a core security challenge: ensuring agents can request work but cannot modify their own spending limits. The recommended architecture separates authority into three boundaries — policy ownership, reservation before execution, and reconciliation against measured usage — each managed by distinct principals with separate credentials. Before any chargeable work begins, a maximum charge must be reserved, and the ledger must enforce that committed plus reserved amounts never exceed the customer's ceiling. Settlement should occur within the same transactional domain as the reservation, using authenticated meter data rather than agent-supplied figures. OWASP's Secrets Management guidelines are cited as a reference for keeping administrative credentials out of the agent's runtime reach.