PayPal BFF components

Component	Responsibility
Create-order route	Validate item identifiers and quantities, reconstruct trusted totals, and request a Sandbox order.
Capture-order route	Validate the order reference and capture through PayPal Sandbox.
PayPal client	Acquire a server-side access token, apply timeouts, and map vendor failures without exposing credentials.
Catalog pricing boundary	Reject unknown items and browser-supplied prices.

Production endpoints are prohibited. Runtime configuration must explicitly select sandbox and provide credentials through the approved secret path.