A2A Registry Integration Guide

ARPA v0.9.3 aligns its A2A profile with the emerging registry model while preserving ARPA’s authority-control boundary. The integration has three layers: portable Agent Card, registry Publication Projection, and caller-specific Authorization Overlay.

flowchart TD
  P[Publisher / Agent Provider] --> C[A2A Agent Card]
  C -->|exact URI + digest| R[ARPA Publication Projection]
  R --> L[List / structured discovery]
  R --> V[Resolve]
  R --> S[Immutable snapshot/reference]
  L --> Q[Candidate agent]
  V --> Q
  S --> E[Audit / replay evidence]
  Q --> A[ARPA authority evaluation]
  A -->|permit| I[Invoke A2A endpoint]
  A -->|deny / indeterminate| D[Do not invoke]

Registration and publication

A publisher supplies or references an Agent Card. The registry records the exact source URI, content digest, observation time, disclosure class, lifecycle status and source-record provenance. The registry does not rewrite the card to encode local entitlements.

Discovery

GET /agents is the ordinary discovery surface. Visibility is filtered by caller context. Unauthenticated requests receive only public projections; authenticated callers may receive additional projections permitted by local policy. Structured filters cover protocol version, skill, capability, namespace and disclosure class. Semantic/vector search is optional and outside the base profile.

Resolve and snapshot

GET /agents/{agent_id} resolves the current ARPA view. Where an Agent Card representation participates in a consequential authority or execution decision, the registry retains an immutable digest-bound snapshot/reference so the decision can be reproduced.

Compatibility

The repository compatibility classifier emits compatible, breaking, or indeterminate. Adding advertised functionality is normally compatible; removing skills, interfaces, security schemes, input/output modes, or disabling an existing capability is breaking. The classifier is evidence for change management, not proof of capability or authority.

Governance invariants

Discoverability is not authority.
Publication is not delegation.
Endpoint authentication is not permission to act.
A card signature establishes integrity relative to its signer, not issuer competence or governance recognition.
Authoritative ARPA suspension, revocation, delegation expiry and recognition withdrawal override published card content.

Federation posture

ARPA v0.9.3 does not mandate centralized catalogs, a federation-of-catalogs architecture, a federation-of-peers architecture, xRegistry, SPIFFE/mTLS, DCAT/JSON-LD, DIDs, or a specific search engine. Those can be profiled or adapted without changing the publication/authority separation.

Evidence produced

The release gate checks exact URI preservation, visibility filtering, immutable snapshots, compatibility classification and non-implication of authority. Results are written to artifacts/interoperability/a2a-registry-report.json and artifacts/interoperability/a2a-registry-evidence-bundle.json.

Actor-chain attribution

A2A issue #2028 is tracked as an informative proposal. If a deployment carries actor-chain metadata, preserve it as attribution/audit input and resolve authority independently through ARPA. A monotone chain is only internally consistent; it is not proof of grant. Keep missing, unresolvable, invalid, revoked/expired, and denied states distinct, and bind evidence references to context where replay could alter meaning.