Touchstone Assay

Touchstone Assay publishes Dated SIU — the benchmark price of AI inference work, measured by actually buying inference against a versioned task basket, not by surveying list prices.

The two hard invariants

1. The print is computed from executed runs only. Published list prices inform exchange rates and are never inputs to the print.
2. The escrow contract is non-custodial. Funds move only to the pre-agreed seller, back to the buyer, or to the fee treasury — no admin path to user money exists in any code path.

How to run a print

Placeholder — wired up once packages/print exists.

Docs

• CLAUDE.md — vocabulary, invariants, build boundaries.
• docs/build1-spec.md — the Build 1 engineering specification.
• docs/plan.md — orientation, dependency order, and open risks.

Deployments

Base Sepolia

Chain ID 84532. Deployed 2026-08-18 from commit 7b1d6ed.

Full record — transaction hashes, block numbers, constructor arguments, compiler settings, and live smoke-test results — is canonical in data/deployments/base-sepolia.json. This README section is a convenience view generated from that file (node scripts/generate-readme-deployments.mjs) and must never be hand-edited to disagree with it.

Not deployed to mainnet. Requirements before it can be:

• treasury MUST be a Safe/multisig, not an EOA. It is immutable with no setter, so a lost key makes fee revenue permanently unrecoverable and the only remedy is redeploying the escrow and migrating every integrator.
• Generate TOUCHSTONE_PUBLISHER_KEY on an air-gapped machine. The testnet key used here has passed through repository-adjacent files.
• Deploy.s.sol is chain-guarded to 84532; a mainnet deployment needs its own script and its own review.

Verify a print independently

A print's own signature and public_key fields only prove internal consistency — that some key signed this exact body. They cannot prove that key is Touchstone Assay's, because a tampered file could carry a self-consistent signature over a different key entirely. Closing that gap is the entire reason the publisher key is coupled to TouchstoneAttestation: the contract's publisher address is immutable and lives outside the file, so it is a truth a tampered print cannot rewrite.

The loop:

1. Recompute the print's body hash independently (JCS-canonicalise the body minus its signature fields, keccak256 it).
2. Recover the signer's address from the raw {signature, hash} pair — not read from the print's own public_key field. (Recovery yields two address candidates, since the stored signature carries no recovery bit; exactly one matches a real signer.)
3. Compare the recovered address against TouchstoneAttestation.publisher(), read live from chain.
4. Confirm the same body hash is anchored (postedAt(bodyHash) > 0).

BASE_SEPOLIA_RPC_URL=... pnpm --filter @touchstone/print run verify-onchain <print-id> base-sepolia

No TOUCHSTONE_PUBLISHER_KEY is needed — this command only reads. Real output against the worked-example print (docs/siu-worked-example.md, Dated SIU $0.0383) anchored on Base Sepolia:

On-chain publisher():        0x284ff2F8605Ff8AFeDa6959B856Bb7E6d48f845a
Recovered signer candidates: 0x7ab67ceaaf33b21336b0481b3e8a867b70503e35, 0x284ff2f8605ff8afeda6959b856bb7e6d48f845a
  -> MATCH (recovery id 1): this print was signed by the on-chain publisher.

postedAt(bodyHash): 1787035752
  -> ANCHORED at 2026-08-18T06:49:12.000Z

VERIFIED: signature matches the on-chain publisher AND the hash is anchored.

A print signed by any other key — or never anchored at all — reports NOT VERIFIED and exits non-zero (verified live against Base Sepolia with an unrelated key: neither recovered candidate matched publisher(), and postedAt read 0).