docs(x402): spike #206 — hand-roll verdict + proven local EIP-3009 facilitator loop#211
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…cilitator loop Standalone spike feeding two build decisions into #34: Q1 (dep decision): hand-roll the EIP-3009 TransferWithAuthorization in deckard-core (the cow_types alloy sol! precedent), NOT x402-types. Proven byte-for-byte: hand-roll, x402-rs, foundry cast, and the deployed USDC contract all agree on typehash/digest/ signature. Pulling x402-chain-eip155 into the trust core = 222 transitive crates (3x rustls, hyper, reqwest, full alloy-provider stack) for zero cryptographic gain. Q2 (local loop): PROVEN on anvil --fork-url $RPC_URL_SEPOLIA --fork-block-number 10822990. Self-hosted x402-rs facilitator (eip155:11155111 -> fork, no Docker) runs 402 -> sign -> /verify -> /settle end-to-end against real Circle USDC FiatTokenV2_2: USDC moves, nonce consumed, facilitator pays gas, replay rejected. Go: stay on the Sepolia fork. Recipe reproduces from a cold start via run.sh given $RPC_URL_SEPOLIA. Spike code (digest-cmp) is self-excluded from the deckard workspace; no workspace Cargo.toml/lock changes. Refs #206, feeds #34.
… vector Per review: the Q1 evidence (byte-identical digests, transcript) and the KAT vector stay; the throwaway comparison crate is dropped from the repo (it was never a workspace member).
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Closes the #206 spike. Docs-only: adds a reproducible recipe + the two build decisions #34 needs before it starts. No code, no workspace
Cargo.toml/Cargo.lockchanges (the spike harness underdigest-cmp/is self-excluded from the deckard workspace via an empty[workspace]table).What this proves
Q1 — build shape → hand-roll in
deckard-core, notx402-types.A 6-line
alloy sol!TransferWithAuthorization(thecow_types.rsprecedent) produces the byte-identical EIP-712 typehash, digest, and signature as x402-rs's own type — cross-checked four ways (hand-roll, x402-rs, foundrycast wallet sign, and the deployed USDC contract accepting it on-chain). Pullingx402-chain-eip155into the#![forbid(unsafe_code)]trust core drags 222 transitive crates (3×rustls,hyper,reqwest, fullalloy-providerstack) for zero cryptographic gain. Use x402-rs only as the demo-fixture facilitator binary, never a build dep — as #34 already planned.Q2 — the fully-local loop works → stay on the Ethereum Sepolia fork.
402 → sign EIP-3009 → facilitator /verify → /settle → on-chainruns end-to-end against the real Circle USDCFiatTokenV2_2onanvil --fork-url $RPC_URL_SEPOLIA --fork-block-number 10822990, with a self-hosted x402-rs facilitator (eip155:11155111 → fork, no Docker). Asserted: USDC moved, nonce consumed, gas paid by the facilitator (not the buyer), replay rejected.run.shreproduces it from a cold start.Spec corrections v2 forced (detailed in the doc, folded into the #34 decision comment)
eip155:11155111); v1 has no network name for Ethereum Sepolia."USDC", version"2"— not mainnet's"USD Coin". The 402extramust carry{assetTransferMethod:"eip3009", name:"USDC", version:"2"}.X-Paymentv1 /Payment-Required+Payment-Signaturev2) is agent-side transport; the facilitator API is plain JSON.SignatureCheckerrejects the EOA signature. Use fresh codeless keys.Files
docs/research/x402-spike/README.md— the full report + evidence transcriptsrun.sh— self-contained proof of the loopfacilitator-config.json,typed-data.json,eip3009-kat.json— fixtures + the KAT vector for x402 phase 2: exact/EIP-3009 payments on the Ethereum reference path, fully local demo loop #34digest-cmp/— the Q1 hand-roll-vs-x402-rs harness (standalone; git dep on x402-rs)Decision comment posted on #34.