Raise Accelerated Checkouts coverage above 85%

[markmur]

Add regression coverage for Apple Pay address validation and checkout fallback, discount aggregation and subscription shipping, and Storefront response decoding and error descriptions. The tests check customer-visible fields, amounts, recovery details, and retained response data.

ShopifyAcceleratedCheckouts line coverage increases from 77.31% to 86.83% with no production code or coverage-exclusion changes, preparing the target for the following 85% threshold PR.

Stack

• Cover native protocol model serialization contracts #936
• Cover protocol runtime mapping and JSON contracts #935
• Report protocol runtime and generated coverage separately #934
• Enforce 85% line coverage for each Swift SDK target #929
• Raise Accelerated Checkouts coverage above 85% #928
• Enforce 85% Android SDK line coverage #927
• Report Swift and Android test coverage #924
• Aggregate existing JavaScript coverage reports into one PR comment #948
• Enforce 85% test coverage thresholds #923

[github-actions]

Bundle Size Budgets

Budget	Size	Limits	Result
—	—	—	➖ No configured budgets affected

Bundle and package size

Web bundle sizes cover shipped runtime JavaScript. Package sizes cover the full published archive, including any source maps, declarations, and documentation it contains.

Platform	Measurement	Compression	Base	Head	Delta
-	-	-	-	-	-

How sizes are measured

Measured from the PR base SHA and PR head SHA. Web bundle rows sum shipped .js, .mjs, and .cjs files under dist/, excluding source maps and declarations. The gzip bundle size sums files compressed individually with gzip -n -9. npm package sizes are gzip-compressed .tgz archives; Android AAR sizes are ZIP archives. Package sizes are not final app binary sizes.