arc-honest-money

Four dependency-light primitives for verifiable agent money on Arc, extracted from Cronus Capital. MIT. Fork freely.

npm i arc-honest-money

Importing this package pulls in zero runtime dependencies, reads no environment variables and has no side effects. viem is an optional peer dependency, loaded lazily only by the one function that signs a transaction.

verifyX402Payment - prove you were paid

A seller must be able to prove payment, not assume it. Given a tx hash, confirm an on-chain USDC Transfer of at least minAmount to your payTo. Raw JSON-RPC, no SDK. Works for plain transfers and memo-wrapped ones, because the inner USDC Transfer is still emitted.

const r = await verifyX402Payment({ txHash, payTo, minAmount: "20000" })
// { paid: true, payer: "0x...", amount: "20000", block: "0x2a" }
// underpaid -> { paid: false, reason: "underpaid: ...", amount, minAmount }

decideSpend - cap agent spend in code, not in the prompt

Money safety belongs in code. A pure, deterministic gate over atomic units: a model may propose a number, but the caller enforces the hard cap, so a hallucinated or adversarial amount can never overspend. Fails closed on malformed input, exact at any magnitude.

decideSpend({ spentAtomic: "900000", amountAtomic: "200000", capAtomic: "1000000" })
// { allowed: false, reason: "exceeds remaining budget", remainingAtomic: "100000" }

const breaker = createBreaker("1000000")  // in-process; back it with Redis in prod

crossCheck - corroborate a price against a second venue

A single venue can glitch or be manipulated. Compare a primary price against an independent public spot and report the spread. Advisory and fail-open: on any failure agree stays null - it annotates, it never fabricates a price.

await crossCheck("BTC-USDC", 64000, { tolPct: 0.5 })
// { source: "coinbase", altPrice: 64100, spreadPct: 0.1563, agree: true }

payWithMemo - pay with an on-chain reconcilable reference

Pay any x402 resource through Arc's memo wrapper, attaching an indexed reference to the transfer while keeping your own wallet as msg.sender. The same topic always hashes to the same memoId, so payments are groupable on-chain. Requires viem.

const { payment, unlocked } = await payX402WithMemo({
  url: "https://your-endpoint/api/signal?topic=BTC-USDC%20momentum",
  privateKey: process.env.BUYER_PRIVATE_KEY,
  topic: "BTC-USDC momentum",
})

Why these four

Arc's value is verifiable money. These are the pieces of an honest x402 economy: a seller can prove it was paid, a buyer can pay with context, an agent can cap its own spend, and a signal can be cross-checked before it is trusted.

Design rules

• Fail closed on money, fail open on data. A spend decision denies on malformed input; a price cross-check returns agree: null rather than inventing a number.
• Injectable I/O. Every network call accepts a fetchImpl, so the whole surface is testable without a network and without mocking globals.
• Atomic units everywhere. No floats in money paths.
• Importable from a serverless handler. No top-level env reads, no top-level signing.

Status

v0.1.0. Extracted from the Cronus Capital codebase and published so the primitives can be forked and imported on their own. Cronus is migrating its own call sites onto this package module by module, starting with the price cross-check.

Tests

npm test          # 42 tests, no network
npm run selftest

CLI

node src/verify-x402-payment.mjs <txHash> <payTo> <minAmount>
node src/spend-breaker.mjs selftest
node src/price-crosscheck.mjs BTC-USDC 64000 0.5
node src/pay-with-memo.mjs "BTC-USDC momentum"

License

MIT (c) Cronus Capital