Shopify POS UI Extension: `shopify.cart.addLineItem` Performance Bottleneck

Hey @adamwooding

We’ve fixed the issue where using bulkCartUpdate for duplicate quantity increments could cause cart line prices to show as $0.00 on-device. We’re now avoiding bulkCartUpdate for duplicate adds, which prevents that from happening. This will be in POS 11.9.

The broader cart speed improvements will take a little longer, but the next improvement we’re working on is adding the ability to include cart properties in the same call as adding a line item. This will be apart of the 2026-07 ui extensions release.

Hope that helps give merchants a clearer update for now. Thanks!