PACT: Private Agent Consent and Trust Profile for OAuth 2.1 and CIBA

PACT (Private Agent Consent and Trust Profile) is a security profile of OAuth 2.1 for privacy-preserving agent delegation. It extends VEIL and composes OIDC CIBA Core 1.0 and OAuth Token Exchange (RFC 8693). PACT defines a durable-host plus ephemeral-session control plane, a delegation token claim vocabulary, runtime identity proofs using Ed25519 JWTs, capability grants with typed constraints and usage limits, risk-graduated consent routing, and claim narrowing on token exchange to non-agent audiences.