Integration: Event-driven (sequenced) attestation freshness — WTRMRK on-chain model

[aeoess]

Context

On A2A#1712, @64R3N proposed event-driven freshness as an alternative to timer-driven freshness for attestation evidence. Instead of asking "how old is this attestation?" (timer-based), a receiving party asks "has the agent produced a newer attestation since this one?" (sequence-based).

The APS AttestationFreshness type currently supports snapshot, rotating, and static modes — all timer-based. 64R3N's proposal implies a fourth mode: sequenced, where freshness is determined by position in an append-only attestation log rather than elapsed time.

Proposed Addition

interface AttestationFreshness {
  type: 'snapshot' | 'rotating' | 'static' | 'sequenced'
  validAt: string
  ttl?: number          // rotating (SPIFFE)
  maxAge?: number       // snapshot (TPM)
  sequenceRef?: string  // hash of this entry in the registry
  registryUri?: string  // where to check for newer entries
}

New evaluation function: isLatestInSequence(sequenceRef, registryHead): boolean

Integration Point

WTRMRK's on-chain attestation sequence (Base L2) is the reference implementation for this pattern. Each agent accumulates a tamper-evident chain of attested actions. The sequenceRef would point to the agent's latest entry, and registryUri would point to the on-chain registry.

Open Questions

1. Should sequenced freshness require a live registry query, or can it fall back to maxAge when offline?
2. How does sequence-based freshness interact with cascade revocation — if an agent's passport is revoked, should all entries in its attestation sequence be considered stale?
3. Is counterparty diversity (number of distinct interactions) a better signal than sequence length?

@64R3N — would you be interested in contributing the sequenced freshness spec or test vectors? The SDK is at npm install agent-passport-system with the current freshness types in src/types/passport.ts.