---
id: 01-define-feature-helper
epic: conformance-system-v1
title: defineFeature helper + Instrumented/Captured/Audited brands
type: technical-story
status: in-progress
feature: core-shared
depends-on: []
blocks: [02-boot-assertions]
---

## Goal
Manifest helper + brand types enable type-level enforcement that every
use-case binding is wrapped with `withSpan` + `withCapture`
(and `withAudit` when mutating with audits declared).

## Why
Compile-time feedback is the cheapest layer and the foundation every other
milestone reads.

## Done when
Compile-time TS2322 fires when an unwrapped factory is bound through
`ProductionUseCase<...>`, and `auth.signIn` is rebound through the new slot.

## In scope
- `Instrumented<F>` and `Captured<F>` brand types in `@repo/core-shared/conformance`
- Brand attachment in `withSpan` and `withCapture`
- `Audited<F>` brand and `withAudit` wrapper in `@repo/core-audit`
- `defineFeature` helper + `FeatureManifest` / `UseCaseManifest` types
- `ProductionUseCase<I, O, M>` branded slot type
- `authManifest` declaring `signIn`, `signUp`, `signOut`
- `auth.signIn` rebound through the branded slot

## Out of scope
- `auth.signUp` / `auth.signOut` rebinding through branded slots (separate tasks within this story or a follow-up story; signUp requires `Audited<F>` once we declare its `audits`)
- Boot-time `assertConformance` (story 02)
- ESLint rules reading the manifest (story 03)
- Generator emitting manifest stubs (story 05)

## Tasks
- [ ] Brand types: `Instrumented<F>` and `Captured<F>`
- [ ] `withSpan` attaches `Instrumented`
- [ ] `withCapture` attaches `Captured`
- [ ] `defineFeature` helper + manifest types
- [ ] `ProductionUseCase<I, O, M>` slot type
- [ ] `withAudit` wrapper + `Audited` brand
- [ ] `authManifest` declaration
- [ ] `auth.signIn` rebound through branded slot
- [ ] Negative test: unwrapped factory rejected at type level