remove buyer change in web

[kiftio]

What changes are you making?

It looks like we intentionally removed this from native - so this is aimed at parity. Totally fine to go the otherway and introduce to native though.

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Removes the checkout:buyerChange event (ec.buyer.change protocol message) from the web platform. This includes removing the event class (ShopifyCheckoutBuyerChangeEvent), its associated detail interface (ShopifyCheckoutBuyerChangeEventDetail), the typed addEventListener overload, the protocol message handler, and all related type definitions (CheckoutBuyerChangeEvent, CheckoutProtocolMessageMap["ec.buyer.change"]). The event is also removed from the public exports, the sample app event list, and the README documentation.

The test suite is updated to verify that ec.buyer.change is now treated as an unsupported/ignored notification alongside other unknown methods.

How to test

1. Run the existing test suite: pnpm test in platforms/web.
2. Confirm that the "ignores unsupported notification" test now covers both "customMethod" and "ec.buyer.change".
3. Confirm that no checkout:buyerChange events are dispatched or exported by the package.
4. Verify the sample app no longer lists checkout:buyerChange as a subscribable event type.

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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

Tip

See the Contributing documentation for the full release process per platform.

[kiftio]

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

• hide communication client #288
• remove buyer change in web #290 👈 (View in Graphite)
• Use typed Android JSON-RPC params #300
• Use typed Swift JSON-RPC envelopes #299
• respond to unknown requests with error #289
• ignore unknown messages #287
• main

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

[github-actions]

Web — Coverage Report

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	98.5% (263/267)	88.48% (146/165)	100% (58/58)

[kieran-osgood-shopify]

Buyer change exists in the CheckoutProtocol - not public, but should we go through with removing there till we decide to support?

[markmur]

@kieran-osgood-shopify yeah agree that we should just strip this from the protocol everywhere until we decide to add it. I'll open a PR for this today

[github-actions]

React Native — Coverage Report

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	91.66% (319/348)	87.86% (181/206)	100% (82/82)