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From ucp-agentic-commerce
Implements UCP Checkout via A2A protocol for autonomous agent-to-agent commerce using Agent Cards and structured DataParts. For multi-agent architectures.
npx claudepluginhub orcaqubits/agentic-commerce-skills-plugins --plugin ucp-agentic-commerceHow this skill is triggered — by the user, by Claude, or both
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**Fetch live spec**: Web-search `site:ucp.dev specification checkout-a2a` and fetch the page for the exact message structure, DataPart keys, and Agent Card format.
Implements UCP AP2 Mandates for autonomous agent payments using SD-JWT credentials, JWS merchant signatures, and Agent Payments Protocol in 7-step flow with security lock.
Implements AP2 payment protocol as A2A extension in multi-agent systems: mandates DataParts in messages, Agent Cards for capabilities, payment task flows, and inter-agent communication.
Implements ACP REST checkout API: create, update, retrieve, complete, cancel sessions with state machine, data models, and headers. For merchant endpoints and AI agent flows.
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Fetch live spec: Web-search site:ucp.dev specification checkout-a2a and fetch the page for the exact message structure, DataPart keys, and Agent Card format.
Also review Google's A2A protocol spec for the underlying transport: https://google.github.io/A2A/
A2A (Agent-to-Agent) is a protocol for autonomous inter-agent communication. UCP's A2A binding lets a Platform agent talk to a Business agent using structured messages rather than REST calls.
/.well-known/ucp profile under services.dev.ucp.shopping.a2a.endpoint.DataPart objects. Business agent responds with checkout state in DataPart objects.UCP-Agent header and X-A2A-Extensions header referencing the UCP spec version.| Key | Direction | Purpose |
|---|---|---|
a2a.ucp.checkout | Both | Checkout session data |
a2a.ucp.checkout.payment_data | Platform → Business | Payment credentials for completion |
a2a.ucp.checkout.risk_signals | Platform → Business | Optional risk signals |
ap2.merchant_authorization | Business → Platform | Merchant's JWS detached content signature for AP2 mandate flow |
ap2.checkout_mandate | Platform → Business | SD-JWT+kb credential proving user-authorized agent checkout |
Messages use A2A's standard format:
messageId: Unique ID (used for idempotency)contextId: Session/conversation IDkind: "message"role: "user" (from platform) or "agent" (from business)parts: Array of TextPart and DataPart objectsCheckout data is carried in DataPart with the appropriate key.
The Business agent uses messageId to detect duplicate requests. Task tracking uses taskId with contextId.
Before implementing, fetch the latest sample A2A Business Agent from https://github.com/Universal-Commerce-Protocol/samples (look for the a2a/ directory) to see the reference pattern.