@peac/mappings-a2a bridges PEAC signed interaction receipts and the Agent-to-Agent Protocol (A2A). It validates A2A v1.0.0 Agent Card structures, attaches and extracts PEAC evidence carriers from A2A metadata, and discovers PEAC capabilities advertised by remote agents. All carrier operations enforce transport constraints (64 KB embed limit for A2A).

A2A v0.3.0 compatibility (dual-version Agent Cards, top-level url, kebab-case TaskState normalization, /.well-known/agent.json legacy discovery path) was deprecated in v0.12.3 and removed in v0.13.0 (DD-186). This package accepts A2A v1.0.0 shapes only; see docs/MIGRATION_CURRENT.md for the migration guide.

How Do I Use It?

Validate an A2A v1.0.0 Agent Card

import { normalizeAgentCard } from '@peac/mappings-a2a';

const card = {
  name: 'billing-agent',
  supportedInterfaces: [
    { url: 'https://billing.example.com', protocolBinding: 'http+json', protocolVersion: '1.0.0' },
  ],
};
const normalized = normalizeAgentCard(card);

if (normalized) {
  console.log(normalized.url); // 'https://billing.example.com'
}
// Cards without a valid supportedInterfaces[0].url (including legacy
// v0.3.0 cards that used top-level `url`) return null.

Attach a receipt to A2A TaskStatus metadata

import { attachReceiptToTaskStatus } from '@peac/mappings-a2a';
import type { PeacEvidenceCarrier } from '@peac/kernel';

const carrier: PeacEvidenceCarrier = {
  receipt_ref: 'sha256-abc123...',
  receipt_jws: 'eyJ...',
};

const status = { state: 'TASK_STATE_COMPLETED', metadata: {} };
attachReceiptToTaskStatus(status, [carrier]);
// status.metadata now contains the PEAC extension payload

Extract receipts from A2A metadata

import { extractReceiptFromMetadata } from '@peac/mappings-a2a';

const result = extractReceiptFromMetadata(taskStatus.metadata);
if (result) {
  console.log(result.receipts.length); // number of valid carriers
  console.log(result.meta.transport); // 'a2a'
}

Use the carrier adapter

import { A2ACarrierAdapter, createA2ACarrierMeta } from '@peac/mappings-a2a';

const adapter = new A2ACarrierAdapter();
const meta = createA2ACarrierMeta();

// Extract from incoming TaskStatus
const extracted = adapter.extract(incomingStatus);

// Attach to outgoing TaskStatus
const outgoing = adapter.attach(responseStatus, carriers, meta);

Discover PEAC capabilities from a remote agent

import { discoverPeacCapabilities } from '@peac/mappings-a2a';

const result = await discoverPeacCapabilities('https://agent.example.com');
if (result) {
  console.log(result.source); // 'agent_card' | 'well_known' | 'header_probe'
  console.log(result.kinds); // supported receipt kinds
  console.log(result.carrier_formats); // supported carrier formats
}

Integrates With

@peac/kernel (Layer 0): Evidence carrier types and constants
@peac/schema (Layer 1): Carrier schema validation and receipt ref consistency
@peac/protocol (Layer 3): Receipt issuance and verification
@peac/mcp-server (Layer 5): MCP tool server with A2A interoperability

For Agent Developers

If you are building an AI agent that communicates via A2A and needs signed interaction receipts:

Use normalizeAgentCard() to validate incoming A2A v1.0.0 Agent Cards (cards without a valid supportedInterfaces[0].url return null)
Use attachReceiptToTaskStatus() to embed evidence in outgoing A2A messages
Use extractReceiptFromMetadata() to retrieve evidence from incoming A2A messages
Use A2ACarrierAdapter for a transport-agnostic carrier interface
Use discoverPeacCapabilities() to check whether a remote agent supports PEAC before sending receipts