[E2E] Prepare native preload ready-flow validation

[kyle-schellen]

What changed

• e2e/tests/shared/native-preload-ready.yaml — top-level test, tagged preload/smoke.
• e2e/flows/checkout/assert-native-preload-ready.yaml — the reusable subflow, including the existing enabled-button and close-animation safeguards.
• e2e/flows/app/launch.yaml — enables preload observability for diagnostic runs so the Swift marker stays out of the normal sample accessibility tree.
• e2e/config/matrix.yml — Swift and Kotlin adopt the preload journey. React Native is unchanged, and matrix tests ensure native overrides retain every shared default tag.
• preload added to the journey-tag taxonomy, with matrix and tag tests.

Why

Presenting checkout is not proof that preload was reused. This asserts the whole chain:

preload-state-ready  →  cached WebView selected  →  real checkout content

Both platforms run the same flow with no platform branch, because each sample republishes its SDK's cache-hit diagnostic as the same preload-cache-hit-* identifier (#627). The flow pins both ends — preload-cache-hit-none before presentation, preload-cache-hit-observed after — so a marker stuck on "observed" cannot pass.

Testing

• All e2e/test/*_test.rb — 261 runs, 710 assertions, 0 failures
• Matrix expansion verified: launch,checkout,preload on the two native rows, React Native unchanged
• dev android e2e --tags preload — passed on Android emulator
• dev swift e2e --tags preload — passed on iOS simulator

Stack

1. [E2E] Expose native preload state markers #626 — preload state markers in the samples
2. [E2E] Prove ready preload cache hits on both native samples #627 — proof that the ready cache entry was reused
3. [E2E] Prepare native preload ready-flow validation #631 — this PR: the E2E test and matrix wiring

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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 the SwiftPM/CocoaPods version snippets in platforms/swift/README.md (major version only)

Releasing a new Embedded Checkout Protocol version?

• I have bumped embeddedCheckoutProtocolAndroid in platforms/android/gradle/libs.versions.toml
• I have updated protocol/languages/kotlin/embedded-checkout-protocol/api/embedded-checkout-protocol.api if the public API changed

Releasing a new Android version?

• I have bumped checkoutKitAndroid in platforms/android/gradle/libs.versions.toml
• 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.

[kyle-schellen]

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

• [E2E] Prepare native preload ready-flow validation #631 👈 (View in Graphite)
• [E2E] Prove ready preload cache hits on both native samples #627
• [E2E] Expose native preload state markers #626
• main

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

[bitrise]

Install this build

Open Tophat, select your target device, then click Install. Links open on the Mac running Tophat.

SDK	Install
React Native	Install with Tophat
Swift	Install with Tophat
Kotlin	Install with Tophat

Checkout Kit E2E results

Status	Suite	Target	Platform	OS version tag	Device
✅	react-native-ios	react-native	ios	latest	iPhone 15 iOS 27 Beta
✅	react-native-android	react-native	android	latest	Google Pixel 9 Android 17.0
✅	kotlin-android	kotlin	android	latest	Google Pixel 9 Android 17.0
✅	swift-ios	swift	ios	latest	iPhone 15 iOS 27 Beta