ACP merchant endpoint

packages/commerce/src/acp/ implements the merchant side of the Agentic Commerce Protocol so external buyer agents (e.g. ChatGPT shopping) can discover the catalog and check out, mounted at /acp.

Method + path	Purpose
GET /acp/feed	paginated product feed (?limit&offset), OpenAI product-feed shape
POST /acp/checkout_sessions	create a session from {items, buyer, fulfillment_address}
GET /acp/checkout_sessions/:id	retrieve
POST /acp/checkout_sessions/:id	update (terminal sessions are no-ops)
POST /acp/checkout_sessions/:id/complete	charge + create order (idempotent)
POST /acp/checkout_sessions/:id/cancel	cancel

Auth: /acp is declared in the commerce plugin’s selfAuthenticatingMounts (threaded into authMiddleware by createApp), so the global JWT middleware skips bearer parsing for it. The router compares Authorization: Bearer … against env.ACP_API_KEY in constant time (src/security/constant-time.ts); when the key is unset the surface returns 503 not_configured. Single-merchant: sessions belong to env.ACP_MERCHANT_TENANT (default default).

Pricing is server-side only — the buyer agent supplies items, address, and a payment token, never amounts. complete rebuilds the session to lock pricing, then settles a Stripe Shared Payment Token by creating + confirming a PaymentIntent (delegated payment: buyer credentials never reach the Worker). Sessions persist in D1 acp_checkout_sessions (full session JSON with status / order_id promoted to columns).

Payment idempotency for complete is shared with the conversational checkout path — see Conversational shopping.