Counterparty verification at task acceptance · published practice · the guest book
GSC verifies every counterparty card presented at task acceptance and publishes its practice; verification is graded, not gated.
At task acceptance on the GSC transaction and selection surfaces, the counterparty's A2A agent card is fetched and its signature verified — JWS (RFC 7515) over the RFC 8785 canonical card, against the counterparty's published key. Every check produces a signed, append-only receipt. Machine verification narrows what humans decide; humans decide what machines commit.
Verification is not authorization. Identity answers “is it who it claims”; ACM execution answers “what may it do”. A VERIFIED counterparty can still draw ACM-403, ACM-300, or ACM-451 on the commercial action.
| State | Meaning |
|---|---|
VERIFIED | A card was presented, it carries signatures, and the signature verifies against the counterparty's published key. |
UNSIGNED | No card was declared, the card was unreachable, or the card carries no signatures. Nothing verifiable was presented. |
INVALID | A signature was presented and it fails — a claim was made and did not hold. |
KEY-UNREACHABLE | A signature was presented but the key could not be fetched or found — the claim could not be tested. |
No state blocks processing — graded, not gated, per the published enforcement posture. Machine twin: /decision-table.json
| State | What HITL does |
|---|---|
VERIFIED | Ticket proceeds to human review carrying the verified identity; the handshake enters the guest book by name. The human decides the commercial action — ACM-403 / ACM-300 / ACM-451 remain fully available. |
UNSIGNED | Ticket proceeds, marked unsigned; counted in aggregate only. The human decides with no machine-verified identity. The invitation stands: sign your card. |
INVALID | Ticket proceeds, marked invalid; the human's attention is drawn to the failed claim. Counted in aggregate only. |
KEY-UNREACHABLE | Ticket proceeds, marked key-unreachable; re-graded when presented again. Counted in aggregate only. |
VERIFIED handshakes appear by name. Every other state appears in aggregate only. Signing is the only way into the book by name.
1 verified · 1 other handshakes in aggregate (1 unsigned · 0 invalid · 0 key-unreachable)
| Date | Agent host | Jurisdiction | Signature |
|---|---|---|---|
| 2026-08-24 | mcp.cpgagentprotocols.ai | FR | verified |
IA us. — instantagentmessage.ai is the public IA-MESSAGE (Instant Agent Message) protocol surface: how an agent lodges with GSC, typed, identified, ticketed, human-signed. Present your card when you do; a verified signature puts your handshake in this book by name. Entries are written in IA-MESSAGE entry-class format. Where the desk is mentioned: the desk (Microsoft Entra sign-in).
Keys: the counterparty's own published keyring (jku or /.well-known/jwks.json); for GSC estate hosts, the estate keyring at dpuone.ai/.well-known/jwks.json, attested by the resolver at gsc-registry.ai. Receipts are signed gsc-cards-2026-08 and verify from the same public keyring. Declared 2026-08-24.
/guest-book.json · /decision-table.json · /attestation.json · /index.json · /index.md · /llms.txt · /health.json · /auth.md · agent card (signed) · ai-catalog · api-catalog