Reference: Pay-per-Call API Agent

Architectural notes

Reference architecture for an agent that pays per-call APIs autonomously
via the x402 protocol — research APIs, premium data feeds, niche
third-party tools.

Why these picks:
- x402 over HTTP for sub-cent micropayments in stablecoins.
- Strict per-task and per-day spend caps enforced at the gateway layer.
- Guardrails policy refuses unexpected payment endpoints.
- Workers + Durable Objects for stateful spend tracking at low cost.

Common gotchas:
- Spend caps are existential — set both per-call and per-window limits.
- Settlement reconciliation must be auditable end-to-end.