Build an agent application that uses ACP's April 2026 Cart, Feed, Orders, and MCP capabilities to manage the full purchase lifecycle via the updated protocol

Steps

1. Review the ACP changelog for the April 17, 2026 release which added Cart, Feed, Orders, Authentication, and MCP capabilities to the protocol; pull the latest spec from github.com/agentic-commerce-protocol/agentic-commerce-protocol.
2. Implement the Cart endpoint (POST /cart) which replaced the earlier single-step checkout session in the updated spec; the cart allows multi-item accumulation, shipping option selection, and discount application before triggering payment.
3. Subscribe to the Orders feed endpoint so your agent can poll or receive webhooks on order status changes (confirmed, shipped, delivered, cancelled) using the new Orders capability added in April 2026.
4. Implement the ACP Authentication flow for the MCP capability: ACP now supports MCP server connections as of the April update, allowing agents to call merchant tools directly via MCP rather than only REST; authenticate using the OAuth 2.0 client credentials flow specified in the Authentication capability.
5. Test the full lifecycle: feed product discovery → cart creation → cart update → checkout (via Stripe SPT) → order status polling; use the ACP sandbox environment for end-to-end testing before pointing to production merchant endpoints.