feat(template): make PDP variants instant

[laugharn]

Summary

• keep the PDP's coherent cached route shell and server-resolved initial variant
• use Hydrogen's product form store to resolve same-product option selections immediately from encoded availability plus sparse adjacent variants
• keep option controls as real links while replacing the URL after client selection, preserving refresh and no-JavaScript behavior
• document the hybrid server/client variant model

Why

The PDP intentionally remains a blocking, coherent product route rather than exposing a generic loading shell. Once the product is loaded, however, variant interaction should not be paced by a route round trip when Shopify already provides enough encoded and sparse variant data to resolve it locally.

Verification

• pnpm --dir apps/template format — passed
• pnpm --dir apps/template codegen — passed
• pnpm --dir apps/template exec next typegen — passed
• pnpm --dir apps/template exec tsc --noEmit — passed
• pnpm --dir apps/template lint — passed
• pnpm --dir apps/template build — passed

pnpm --dir apps/template exec hydrogen gql check --fail-on-warn is currently blocked by Hydrogen/gql.tada under the workspace's TypeScript 7: TypeError: a.parseConfigFileTextToJson is not a function. The repository GraphQL codegen validated and generated the changed documents successfully.

The session's tracked apps/template/lib/shopify/transforms/image-placeholders.test.ts does not exist on main; it belonged to the earlier demo branch and could not be run here.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
shop-docs	Ready	Preview, v0	Aug 22, 2026 4:21pm
shop-template	Ready	Preview, v0	Aug 22, 2026 4:21pm