[Draft] Expand protocol to expose full envelope

[markmur]

What changes are you making?

The protocol layer now emits the full JSON-RPC envelope (params: { checkout } / params: { error }) as the UCP spec defines it, instead of pre-narrowing descriptors down to bare payloads. Each host kit re-narrows back to its ergonomic bare-payload API, so public consumer APIs are unchanged — the narrowing just moves from the protocol into the kits.

Scope: ec.* methods only. RN native bridges/JS, sample apps, and Models.* are untouched.

Protocol descriptors now carry the envelope

Kotlin (EmbeddedCheckoutProtocol.kt, generated):

// Before — descriptor pre-narrowed to the bare payload
public val start: NotificationDescriptor<Checkout> = notificationDescriptor(
    method = Event.start,
    paramsSerializer = CheckoutParams.serializer(),
    decode = { it.checkout },
)

// After — descriptor exposes the full params envelope
public val start: NotificationDescriptor<CheckoutParams> = notificationDescriptor(
    method = Event.start,
    paramsSerializer = CheckoutParams.serializer(),
    decode = { it },
)

Swift (EmbeddedCheckoutProtocol+Event.swift, generated) and TypeScript (ProtocolNotifications.ts, generated) get the same treatment — descriptors decode to JSONRPCCheckoutParams / { checkout } rather than Checkout.

Kits re-narrow to keep their public APIs identical

Swift kit (CheckoutProtocol.swift):

// Before
public static let start = EmbeddedCheckoutProtocol.Event.start
// After
public static let start = EmbeddedCheckoutProtocol.Event.start.map { $0.params.checkout }
public static let error = EmbeddedCheckoutProtocol.Event.error.map { $0.params.error }

Android kit (CheckoutProtocol.kt):

// Before
public val start: NotificationDescriptor<Checkout> = EmbeddedCheckoutProtocol.start
// After
public val start: NotificationDescriptor<Checkout> = EmbeddedCheckoutProtocol.start.map { it.checkout }
public val error: NotificationDescriptor<ErrorResponse> = EmbeddedCheckoutProtocol.error.map { it.error }

Web kit (checkout.ts) narrows at the handler site:

// Before
.on(Event.start, (checkout) => { … })
// After
.on(Event.start, ({ params: { checkout } }) => { … })

The Android kit's public .api baseline is unchanged (JVM erasure); the protocol module's .api gains only the two new public CheckoutParams / ErrorParams classes.

[github-actions]

Web — Coverage Report

Lines	Statements	Branches	Functions
	99.55% (222/223)	85.58% (95/111)	100% (61/61)

[github-actions]

React Native — Coverage Report

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

[github-actions]

Package Size

Platform	Artifact	Base	Head	Delta
Web	npm tarball	66.6 KiB	67.0 KiB	+445 B
React Native	npm tarball	99.4 KiB	100.2 KiB	+743 B
Android	release AAR	160.8 KiB	161.2 KiB	+418 B

Web file breakdown

File	Base	Head	Delta
dist/index.js.map	179.9 KiB	182.8 KiB	+2.9 KiB
dist/index.js	47.6 KiB	48.0 KiB	+494 B
dist/custom-elements.json	38.0 KiB	38.0 KiB	0 B
src/checkout.ts	26.5 KiB	26.6 KiB	+98 B
README.md	16.4 KiB	16.4 KiB	0 B
dist/checkout.d.ts	6.9 KiB	6.9 KiB	0 B
src/checkout.types.ts	4.1 KiB	4.1 KiB	0 B
dist/checkout.types.d.ts	3.0 KiB	3.0 KiB	0 B
package.json	2.9 KiB	2.9 KiB	0 B
src/checkout.styles.ts	2.8 KiB	2.8 KiB	0 B
src/utils.ts	1.7 KiB	1.7 KiB	0 B
dist/utils.d.ts	1.4 KiB	1.4 KiB	0 B
src/index.ts	1.2 KiB	1.2 KiB	0 B
LICENSE	1.1 KiB	1.1 KiB	0 B
dist/index.d.ts	738 B	738 B	0 B
src/checkout-web-component.ts	271 B	271 B	0 B
dist/checkout-web-component.d.ts	154 B	154 B	0 B
dist/checkout.styles.d.ts	79 B	79 B	0 B

React Native file breakdown

File	Base	Head	Delta
node_modules/@shopify/checkout-kit-protocol/src/generated/Models.ts	85.8 KiB	85.8 KiB	0 B
node_modules/@shopify/checkout-kit-protocol/src/generated/Models.d.ts	53.2 KiB	53.2 KiB	0 B
ios/ShopifyCheckoutKit.swift	15.0 KiB	15.0 KiB	0 B
ios/AcceleratedCheckoutButtons.swift	14.0 KiB	14.0 KiB	0 B
lib/commonjs/index.js	13.1 KiB	13.1 KiB	0 B
src/components/AcceleratedCheckoutButtons.tsx	12.9 KiB	12.9 KiB	0 B
src/index.ts	12.5 KiB	12.5 KiB	0 B
lib/commonjs/components/AcceleratedCheckoutButtons.js	11.4 KiB	11.4 KiB	0 B
android/src/main/java/com/shopify/reactnative/checkoutkit/ShopifyCheckoutKitModule.java	11.1 KiB	11.1 KiB	0 B
lib/module/index.js	10.4 KiB	10.4 KiB	0 B
lib/commonjs/components/AcceleratedCheckoutButtons.js.map	10.3 KiB	10.3 KiB	0 B
lib/module/components/AcceleratedCheckoutButtons.js	10.2 KiB	10.2 KiB	0 B
node_modules/@shopify/checkout-kit-protocol/src/generated/ProtocolNotifications.ts	8.5 KiB	10.0 KiB	+1.5 KiB
lib/module/components/AcceleratedCheckoutButtons.js.map	9.1 KiB	9.1 KiB	0 B
src/index.d.ts	8.9 KiB	8.9 KiB	0 B
lib/module/index.js.map	8.2 KiB	8.2 KiB	0 B
src/present-dispatcher.ts	8.0 KiB	8.0 KiB	0 B
lib/commonjs/index.js.map	7.7 KiB	7.7 KiB	0 B
node_modules/@shopify/checkout-kit-protocol/src/generated/ProtocolNotifications.d.ts	4.5 KiB	6.8 KiB	+2.3 KiB
lib/commonjs/present-dispatcher.js	6.8 KiB	6.8 KiB	0 B
…and 105 smaller files

Android file breakdown

File	Base	Head	Delta
classes.jar	170.2 KiB	170.6 KiB	+417 B
res/layout/dialog_checkout.xml	1.3 KiB	1.3 KiB	0 B
proguard.txt	798 B	798 B	0 B
AndroidManifest.xml	578 B	578 B	0 B
res/values/values.xml	564 B	564 B	0 B
R.txt	522 B	522 B	0 B
res/drawable/close.xml	431 B	431 B	0 B
res/menu/checkout_menu.xml	354 B	354 B	0 B
META-INF/com/android/build/gradle/aar-metadata.properties	157 B	157 B	0 B

Measured from the PR base SHA and PR head SHA. The file breakdown shows uncompressed sizes within each package artifact, so individual files do not sum to the compressed artifact total. This comment reports package artifact sizes only; it is not a final app binary-size report.