[Swift] Add preload state observability

[markmur]

Adds observable lifecycle state to preloaded checkouts on iOS. preload(checkout:) returns a retained CheckoutPreload handle that exposes the current state and emits transitions — .loading → .ready → .expired, .failed(reason:) for HTTP, navigation, and keep-alive failures, and .idle on manual invalidation. State is driven from a single transition choke point in the preload cache and broadcast to a weak observer, so consumers can drive spinners or fall back to a fresh preload when a warm entry lapses.

CheckoutPreload is an ObservableObject, so you can observe it with a closure, Combine's $state, or directly in SwiftUI.

Observe with a closure

// Retain the handle for as long as you want to observe.
checkoutPreload = ShopifyCheckoutKit.preload(checkout: url)
checkoutPreload?.onStateChange = { state in
    switch state {
    case .loading:
        break
    case .ready:
        presentCheckout(url)
    case .expired:
        // warm entry is gone — kick off a fresh preload
        break
    case .failed(let reason):
        print("preload failed: \(reason)")
    case .idle:
        break
    }
}

onStateChange fires immediately with the current state on assignment, then on every transition.

Read the current state synchronously

let checkoutPreload = ShopifyCheckoutKit.preload(checkout: url)
// Synchronously check the current state of the cache
if checkoutPreload.state == .ready {
    // do something
}

Observe in SwiftUI

struct PreloadStatus: View {
    @ObservedObject var preload: CheckoutPreload

    var body: some View {
        switch preload.state {
        case .ready:
            Text("Ready")
        case .loading:
            ProgressView()
        default:
            Text("Not ready")
        }
    }
}

Fire-and-forget warming

// @discardableResult — warm the cache without retaining a handle to observe.
ShopifyCheckoutKit.preload(checkout: url)

[markmur]

• [Android] Evict preloaded checkout under memory pressure #453
• [Swift] Evict preloaded checkout under memory pressure #447
• [Android] Scope preload state to per-cache entry #455
• [Android] Add preload state observability #451
• [Swift] Scope preload state to per-cache entry #454
• [Swift] Add preload state observability #445 👈 (View in Graphite)
• main

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[github-actions]

React Native — Coverage Report

Lines	Statements	Branches	Functions
	91.85% (327/356)	87.98% (183/208)	100% (86/86)

[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
✅	tests/shared/launch-smoke.yaml	swift	ios	latest	iPhone 15 iOS 27 Beta