Build Data

Create the feature's data/ layer (pure spec; depends on nothing but @adobe/data and other data/ declarations):

• one namespace folder per data type — <type>/{<type>.ts, public.ts, <helper>.ts} (+ schema.ts only when a runtime boundary needs it);
• data/state/ — the State aggregate plus its pure transforms/derivations.

Always create data/state/ — even for a shell feature whose only field is a boolean or enum. A feature with ECS resources/transactions but no State is incomplete: the transaction must wrap a pure transform, not invent the logic. In rare circumstances, there may be no real state in a feature in which case the state type = {}

The hand-authored type in <type>.ts is the source of truth. The schema is optional up front — add schema.ts only when a runtime boundary (persistence, wire, or an ECS component/resource) needs one, write it to match the type, and pin it with type _Pin = Assert<Equal<Schema.ToType<typeof schema>, <Type>>> so it cannot drift. Schema.ToType is used only in that assertion, never as the exported type. Helpers are pure and unit-tested. Run this first — every other layer imports data/.

The how is in the auto-loading rules: features/data/index.md, features/data/state.md, and global/namespace.md.