Expert guidance for building Shopify Apps using modern best practices. Use when developing Shopify Apps, creating app extensions, working with Shopify APIs (GraphQL Admin/Storefront), implementing webhooks, managing app authentication/authorization, building embedded apps, creating custom app extensions (checkout UI, product subscription, theme extensions), or any Shopify app development task. Assumes Shopify Dev MCP server is available at https://shopify.dev/docs/apps/build/devmcp for accessing Shopify's development resources and documentation.