build-spec

Legacy feature (has `data/state/` or `services/main-service/`)? Extend it in place per the legacy rules; don't migrate unless asked. Create the feature's `spec/` folder, the specification the ECS will be conformed to: - `state.ts` — `State` built from `data/` types (singletons named for resources, `ReadonlyMap` entity collections), pinned with `Conformance.StateMatches`; `create.ts`, `samples.ts`, `public.ts`. - One file per **action** (each operation the app performs) and per **derivation** (each derived value it shows), each with its inert `*.cases.ts`. A real-time feature adds `systems.ts`: one pure function per ECS system it will have, named the same, each with cases, plus `noOp` states every system leaves unchanged. - `transforms.ts` (the barrel of every action and derivation), `spec.ts` (`Conformance.spec`) and `spec.test.ts` (`Conformance.checkSpec`). Build one action or derivation plus its cases at a time. Logic the ECS will share goes into `data/values/` helpers, never here. Gate: `checkSpec` passes. The how is in the auto-loading `features/spec/index.md` rule.