---
name: bff-endpoint
description: Add a screen-shaped read — backend endpoint returning a decision-enriched DTO, regenerated typed client, contracts DTO, adapter with parse boundary, application store, <app-async> in the page. Use for any new data a page needs.
---

# BFF-lite read endpoint (decision DTO)

One screen = one endpoint returning everything that screen needs, **decisions
included**. The FE renders the server's decisions; it never recomputes business
rules (ADR-0001). Per rule choose: **decision flag** (server computes the boolean)
or **config value** (server sends the threshold, FE applies it for instant feedback,
server re-validates as authority).

## Steps

1. **Backend** (`backend/src/BigRegister.Api/`): minimal-API endpoint under `/api/v1`,
   wire DTO in `Contracts/`, rule in `Domain/` with a test in
   `backend/tests/BigRegister.Tests/`. Rejections are ProblemDetails (RFC 7807, 422).
2. **Regenerate the client**: `npm run gen:api` — commits `backend/swagger.json` +
   `src/app/shared/infrastructure/api-client.ts` (CI has a drift check; never edit the generated file).
3. **DTO** in `<context>/contracts/<name>.dto.ts` — plain interfaces/string-literal
   unions. Contracts import **nothing** (lint-enforced): no Angular, no aliases, no relative imports.
4. **Adapter** in `<context>/infrastructure/<name>.adapter.ts` — the only place HTTP lives:

   ```ts
   @Injectable({ providedIn: 'root' })
   export class DashboardViewAdapter {
     private client = inject(ApiClient);
     viewResource() { return resource({ loader: () => this.client.dashboardView() }); }
   }
   // The trust boundary: validate the untrusted shape AND map DTO → domain.
   export function parseDashboardView(json: unknown): Result<string, DashboardView> { … }
   ```

   The mapping may read as an identity copy today — the point is the **types** differ,
   so the compiler forces a real mapping the moment the wire diverges.

5. **Application store** exposes the resource as `RemoteData` (`fromResource`,
   combine sources with `map`/`map2`/`andThen` from `@shared/application/remote-data`).
   UI never imports infrastructure (lint-enforced).
6. **Page** renders through `<app-async>` (`shared/ui/async`) — one of
   loading/empty/error/loaded by construction. Check all four states with the
   dev-only `?scenario=slow|loading|empty|error` toggle.

## Worked example (trace one name through all layers)

`dashboard-view`: `backend/src/BigRegister.Api` endpoint →
`src/app/registratie/contracts/dashboard-view.dto.ts` →
`src/app/registratie/infrastructure/dashboard-view.adapter.ts` (+ spec on `parseDashboardView`) →
`src/app/registratie/application/big-profile.store.ts` → dashboard page.

## Verify

```bash
cd backend && dotnet test && cd ..
npm run gen:api && git diff --exit-code src/app/shared/infrastructure/api-client.ts
npm test && npm run lint && npm run build
```
