[3/6] Add POS List web component types

[ajanth-u]

Background

The 2026-10 POS UI Extensions surface needs a virtualized list component for structured, incrementally loaded data. The public shape is under TAG review in Shopify/ui-api-design#1576.

Solution

Add the s-pos-list web component contract to the 2026-10 release branch:

• structured rows with labels, up to three subtitles, badges, images, trailing labels, chevrons, and toggle state
• per-row onClick callbacks that receive the callback event; row context is held by each callback's closure
• imageDisplayStrategy, loadingMore, and loadmore support
• a header slot for composable content above the rows; no component-owned title
• availability on supported POS action extension targets
• default and incremental-loading examples
• a minor changeset

The web-component names intentionally replace legacy React-oriented names: data becomes rows, isLoadingMore becomes loadingMore, and onEndReached becomes loadmore / onLoadMore.

Alternatives considered

1. Restore the legacy List contract unchanged — rejected because React-specific names and listHeaderComponent do not fit the web-component surface.
2. Add a title property — rejected because headings compose outside the list or through the header slot.
3. Add a component-level click event carrying row data — rejected because row activation is modeled by per-row onClick callbacks, with row context already available through the closure.

Verification

• yarn build
• yarn type-check
• yarn test (no related Jest suites)
• Prettier on all changed files
• Focused ESLint: StandardComponents.ts passes; generated declarations and examples are intentionally ignored by this repository's ESLint configuration
• Full yarn lint reaches only pre-existing generated checkout/preact.js and customer-account/preact.js errors after yarn build

Dependencies

This draft is blocked on approval of Shopify/ui-api-design#1576. End-to-end availability also requires the POS host implementation linked below.

After this PR merges, regenerate the 2026-10 POS reference data in World before the Shopify Dev documentation PR can merge.

Related PRs

• API design: https://github.com/Shopify/ui-api-design/pull/1576
• POS host implementation: https://meteorite.shopify.io/repos/shop/world/pulls/2030122
• Shopify Dev documentation: https://meteorite.shopify.io/repos/shop/world/pulls/2030135

🎩

Manual POS verification is intentionally deferred to the author.

Checklist

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

[ajanth-u]

/snapIt

[ajanth-u]

/snapit

[shopify-github-actions-access]

🫰✨ Thanks @ajanth-u! Your snapshots have been published to npm.

Test the snapshots by updating your package.json with the newly published versions:

"@shopify/ui-extensions": "0.0.0-snapshot-20260901153420",
"@shopify/ui-extensions-tester": "0.0.0-snapshot-20260901153420"

[ajanth-u]

/snapit

[shopify-github-actions-access]

🫰✨ Thanks @ajanth-u! Your snapshots have been published to npm.

Test the snapshots by updating your package.json with the newly published versions:

"@shopify/ui-extensions": "0.0.0-snapshot-20260901162303",
"@shopify/ui-extensions-tester": "0.0.0-snapshot-20260901162303"