A2A Gateway Pattern Example

Demonstrates the PEAC evidence carrier contract with A2A (Agent-to-Agent Protocol) task state transitions. A gateway agent issues one receipt per state change and attaches it to the A2A TaskStatus metadata.

Quick Start

pnpm install
pnpm demo

What It Does

1. Declares PEAC support in an Agent Card extension
2. Issues a receipt at each state transition (submitted, working, completed)
3. Attaches receipts to A2A TaskStatus metadata via the carrier contract
4. Extracts receipts from metadata on the consumer side
5. Verifies each receipt offline

Gateway Pattern

Consumer          Gateway             Agent
   |                 |                  |
   |--- task ------->|                  |
   |                 |-- receipt #1 --> (submitted)
   |                 |                  |
   |                 |-- receipt #2 --> (working)
   |                 |                  |
   |                 |-- receipt #3 --> (completed)
   |<-- receipts ----|                  |
   |                 |                  |
   (verify chain)

Each receipt records the state transition as an observable fact. Receipts are attached to A2A TaskStatus.metadata under the PEAC extension URI.

Agent Card Extension

The agent-card.json file declares PEAC support:

{
  "uri": "https://www.peacprotocol.org/ext/traceability/v1",
  "required": false,
  "params": {
    "supported_kinds": ["commerce", "attestation"],
    "carrier_formats": ["embed"]
  }
}

References

• A2A Carrier Mapping
• Evidence Carrier Contract
• PEAC Protocol