This is the final layer in the design layers framework, where conceptual models and interaction flows become actual interface elements people touch, read, or hear. It's a library of auditing techniques to check whether your surface honors what's been decided below: vocabulary checks against your ubiquitous language, object consistency passes to catch shapeshifters, completeness checks in both directions between breadboard and UI, feedback inventories, hierarchy reviews, accessibility passes. The core discipline is knowing when something is a surface fix versus a symptom of a deeper model or flow problem that needs to be routed back down. Use it when you're producing or auditing an interface and need to make sure nothing slipped through the cracks between layers.
npx skills add https://github.com/jamiemill/layers-skills --skill layers-surface