An AI agent that pays for API data only after verifying the fields are in the document, spending from an on-chain budget vault on Arbitrum.
Fieldcast Buyer Agent is an AI agent that buys document extraction from a paid API (x402) only when the data it needs is actually in the document. A free regex pass runs first; then a model must quote each missing field and the code checks that the quote really occurs in the text. Only then does it pay. On Arbitrum, spending is gated by AgentBudgetVault: per-call cap 0.02 USDC, daily cap 0.10 USDC, and a float cap so the agent wallet cannot hold a working balance. Each release emits an evidence hash of the decision. The model cannot override any cap.
Built during the buildathon (September 2026): AgentBudgetVault.sol (Ownable2Step, per-call / daily / float caps, allowlisted payee, evidenceHash event), Foundry tests 20/20 with 100% line and branch coverage, deploy script, buyer support for Arbitrum Sepolia with vault release and fund flow, gate accepting eip155:421614, demo video. Vault 0x2c48d7f3bd378d64b0ebe7f85d3ae94fcf3d004c on Arbitrum Sepolia. Demo run: skip on a document without the fields, then vault release tx 0x940965bf323e56f938d96663d24043ca5988548feb3841234e10a6a954a0d86d and x402 payment tx 0x2c98152a0ee5e826de3ec383171fb91ebd09d957685358be3b0bf80bfbaaf3ad. The Base buyer agent and x402 gate existed before the buildathon. Testnet only, both wallets are ours, no outside users yet.
Not raised. Solo builder, bootstrapped.