feat(RN): Wire up accelerated checkouts with protocol events

[kieran-osgood-shopify]

Stack Context

This stack is adding Checkout Protocol event support to the React Native wrapper. The parent PR introduces the first protocol event (ec.start) for the imperative present() path; this PR wires the same start event into instance-based accelerated checkout buttons.

What?

• Adds an events?: ProtocolHandlers prop to AcceleratedCheckoutButtons using computed CheckoutProtocol keys.
• Routes native component dispatch envelopes to JS handlers for [CheckoutProtocol.start].
• Connects iOS accelerated checkout buttons to the existing protocol relay.
• Exposes native supported protocol event constants through constantsToExport and warns if JS/native event lists drift.
• Adds tests and sample usage in the RN sample cart screen.

Why?

Consumers need to observe checkout protocol events from declarative component instances, not only from ShopifyCheckout.present(). This keeps the public TypeScript interface consistent across both surfaces while intentionally keeping protocol support scoped to CheckoutProtocol.start for this PR.

How to test

• pnpm --dir platforms/react-native/modules/@shopify/checkout-kit-react-native typecheck
• pnpm --dir platforms/react-native/sample typecheck
• pnpm --dir platforms/react-native test -- AcceleratedCheckoutButtons.test.tsx --runInBand
• pnpm --dir platforms/react-native exec jest --runInBand
• swift test --package-path platforms/react-native/modules/@shopify/checkout-kit-react-native/ios
• Manual iOS simulator validation with agent-device: tapped the sample cart Shop Pay accelerated checkout button and confirmed the [CheckoutProtocol.start] handler ran by observing the checkout start event state during validation.

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Before you merge

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines
• I have read and agree with the Code of Conduct
• I've updated the relevant platform README (platforms/swift/README.md and/or platforms/android/README.md)

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Releasing a new Swift version?

• I have bumped the version in ShopifyCheckoutKit.podspec
• I have bumped the version in platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
• I have updated platforms/swift/CHANGELOG.md
• I have updated the SwiftPM/CocoaPods version snippets in platforms/swift/README.md (major version only)

Releasing a new Android version?

• I have bumped the versionName in platforms/android/lib/build.gradle
• I have updated platforms/android/CHANGELOG.md
• I have updated the Gradle/Maven version snippets in platforms/android/README.md

[kieran-osgood-shopify]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(RN): Include remaining public protocol events from native #186
• feat(RN): Wire up accelerated checkouts with protocol events #181 👈 (View in Graphite)
• feat(RN): Add wiring for protocol events - add ec.start  #170
• feat(RN): replace addEventListener with callback args #119 : 2 other dependent PRs (#125 , #134 )
• feat(react-native): use local android/swift project references #115 : 1 other dependent PR (#116 )
• feat(protocol): add typescript interfaces #114
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

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React Native — Coverage Report

Lines	Statements	Branches	Functions
	92.46% (319/345)	87.62% (177/202)	100% (86/86)

[kieran-osgood-shopify]

still need to work on the key here - if passing a string literal it accept "ec.start" which I'm not sure we want

might be able to make this an enum instead so it has to be a key