Update POS cart api docs to reflect discount per unit allocation

[janezhu918]

Background

Resolves https://github.com/shop/issues-retail/issues/26385

Update documentation for discount allocation change from ACROSS to EACH starting in API version 2026-04.

Solution

Update docs and provide example

🎩

• Ran yarn docs:point-of-sale 2026-04-rc in this repo.
• Ran this to copy over the generated files (temporary command while the migration is finalized):

cp -r /Users/janezhu/src/github.com/Shopify/ui-extensions/packages/ui-extensions/docs/surfaces/point-of-sale/generated/pos_ui_extensions/2026-04-rc \
    /Users/janezhu/world/trees/root/src/areas/platforms/shopify-dev/db/data/docs/templated_apis/pos_ui_extensions/

• In shopify-dev repo (now in the monorepo), run dev server
• Go to your local https://shopify-dev.shop.dev/docs/api/pos-ui-extensions/2026-04-rc/target-apis/contextual-apis/cart-api to see the updated docs:

Checklist

• I have 🎩'd these changes
• I have updated relevant documentation

[github-actions]

🚨🚨🚨 Docs migration in progress 🚨🚨🚨

We are actively migrating UI extension reference docs to MDX in the areas/platforms/shopify-dev zone of the monorepo. This impacts docs for the following surfaces:

• Admin UI extensions
• App Home
• Checkout UI extensions
• Customer account UI extensions
• POS UI extensions

During this migration, please be aware of the following:

.doc.ts files are being deprecated. Changes to .doc.ts files in this repo will not be reflected in the new MDX-based docs. If you need to update docs for a reference that has already been migrated, make your changes directly in the areas/platforms/shopify-dev zone of the monorepo instead.

Doc comments in .ts source files (the comment blocks above types and functions) are also affected. Generating docs from these comments currently requires a newer version of the @shopify/generate-docs library that isn't yet available. Updates to doc comments may not produce the expected output until the migration is complete.

Examples that previously lived in this repo are being moved to the areas/platforms/shopify-dev zone of the monorepo and should be authored there going forward.

What should I do?

• If your PR includes changes to .doc.ts files, doc comments, or examples, please reach out to us in #devtools-proj-templated-refs so we can help ensure your updates are captured correctly.
• If your PR is limited to source code changes (non-docs), you can ignore this notice.

Thanks for your patience while we complete the migration! 🙏

[janezhu918]

• Update POS cart api docs to reflect discount per unit allocation #4231 👈 (View in Graphite)
• 2026-04-rc

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[janezhu918]

Merge activity

• Mar 27, 3:01 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Mar 27, 3:01 PM UTC: @janezhu918 merged this pull request with Graphite.