feat(spec): add environment.price_integrity constraint proposal

[imokokok]

Summary

This RFC proposes environment.price_integrity as a sibling constraint in the
environment.* namespace for autonomous mode (L3) execution.

The constraint requires a verifier to obtain and independently validate a
short-lived, signed oracle attestation before accepting checkout or payment
fulfillment. It composes with environment.market_state from #9 and
environment.wallet_state from #22. All present environment constraints are
conjunctive and fail-closed.

Motivation

A valid Verifiable Intent credential proves that an agent is authorized to act
within a delegated scope. It does not prove that the price data used at L3
execution is fresh, sufficiently corroborated, or free from an observable
integrity failure.

environment.market_state answers whether the venue is open or halted.
environment.price_integrity addresses the separate question of whether the
price data used for the action is trustworthy.

Alternatives considered:

1. Reusing mandate.payment.amount_range would constrain the final amount but
   would not authenticate a price observation or enforce its freshness.
2. A private application-specific field would prevent interoperable composition
   with the other environment.* constraints.
3. A combined market-state and price-integrity receipt would couple different
   issuers, trust roots, TTLs, and failure domains.

Reference implementation

Insight provides the reference implementation:

• OracleSafetyCheck v2 with EIP-712 signed fields;
• quorum and operator-independence gates;
• 600-second receipt validity;
• /.well-known/oracle-keys.json for key and schema discovery;
• /api/v1/safety/attestation/verify for verification;
• /api/v1/safety/attestation/sample for a live signed sample.

The implementation can be independently verified from the published schema and
key document. It is listed as a reference implementation, not an exclusive
provider or endorsement.

SDK and test status

This PR adds the normative specification file only, following the standalone
specification pattern used by PR #9 and PR #22. SDK model and conformance-vector
updates are follow-up work after the working group confirms the wire shape.

The reference implementation has independent tests covering signature recovery,
UID binding, freshness, asset binding, verdict handling, and fail-closed
composition.

Scope

The core specification is protocol-agnostic and does not require AP2, ACP, MCP,
or any other specific agent transport.

Files changed

• spec/environment-price-integrity.md — normative constraint proposal,
  validation algorithm, security considerations, test vectors, failure modes,
  and implementation status.

[LembaGang]

Verification note, Headless Oracle — on the reference implementation named in this PR.

We fetched Insight's published attestation surface (the RFC 8615 key registry and sample endpoint) and independently verified OracleSafetyCheck v2 receipts: EIP-712 typed-data recovery against the published attester address, in our own implementation, not the issuer's verify endpoint, with tamper controls driven red. Schema as published: 26 signed fields, 600-second validity to the second, quorum and independence fields present in the signed payload. First verified 20 August 2026; re-run today against the live surface, same result.

This verifies the artifact's signature, schema, and freshness. The attested values — provider participation, independence assessment — are the issuer's claims, which the receipt makes attributable and refutable; that is its job. Verification is not endorsement: the environment.* family treats every conforming implementation identically, and a reference-implementation listing grants no exclusivity, exactly as this PR's own text states.

One structural note in support of the proposal: price integrity and market state are different predicates — a feed can be sound while a venue is halted, and a venue open on a depegged feed — and the constraint as drafted composes conjunctively and fail-closed with its siblings, consistent with the family-composition discipline already public in PR #9. That is the right shape for a sibling type.

Michael Msebenzi — author, environment.market_state (PR #9); co-author, draft-borthwick-msebenzi-environment-state

[imokokok]

Applied Douglas's review finding: generalised Appendix C.2 Rule 1 to family-wide scope (a verifier MUST treat a missing, malformed, unverifiable, stale, expired, or negative environment.* attestation as a violation). Type-specific fail-closed details remain in sections 2.1, 4.3 and Appendix B.