New `PRODUCT_UNAVAILABLE_IN_BUYER_LOCATION` warning code in the Storefront API Cart

Starting with the 2026-07 version of the Storefront API, the Cart emits a PRODUCT_UNAVAILABLE_IN_BUYER_LOCATION warning when a cart line contains a product that isn't available in the buyer's location.

Each affected cart line returns its own warning. The warning's target is set to the CartLine ID so you can map it back to the line in your UI.

For background on cart warnings and an example of handling them, refer to our docs on cart warnings.