# WP-07 — Brief on the shared idioms + RemoteData MDX

Status: todo
Phase: 1 — FP/DDD core
Depends on: WP-06 (typed `<app-async>`)

## Why

The brief context drifted from the repo's own reflexes: `brief.store.ts` (~lines 22-25)
holds `busy: signal<boolean>` + `lastError: signal<string|null>` + a separate `saveState`
union side by side — representable illegal combos, the exact "second boolean" smell
CLAUDE.md §3 bans. And `brief.page.ts` hand-renders its load lifecycle with `@switch` +
spinner/alert instead of `RemoteData` + `<app-async>` — the only async flow in the app
bypassing the shared molecule.

## Read first

- `CLAUDE.md` §3; `src/app/shared/application/remote-data.ts`
- `src/app/brief/application/brief.store.ts`, `src/app/brief/ui/brief.page.ts`,
  `src/app/brief/domain/brief.machine.ts` (+ spec)
- `src/app/registratie/application/applications.store.ts` (a store doing it right)

## Decisions (pre-made, don't relitigate)

- Transient submit/save state becomes **one** tagged union
  (`Idle | Busy | Failed{error}`), replacing `busy`+`lastError`. `saveState` keeps its
  union shape (align tag style).
- Load lifecycle → `RemoteData` + `<app-async>`; the machine keeps owning the letter's
  _domain_ lifecycle (loading tags move out of the machine only if they purely mirror
  the fetch — keep the seam: RemoteData = fetch, machine = letter).
- Keep the debounced-save sequencing identical; only re-type the state.

## Files

- `src/app/brief/application/brief.store.ts`
- `src/app/brief/ui/brief.page.ts`
- `src/app/brief/domain/brief.machine.ts` + `brief.machine.spec.ts`
- New `src/docs/remote-data.mdx` — title `Foundations/RemoteData & Async`

## Steps

1. Replace the signal trio with one union signal; update consumers (letter-composer bar,
   autosave status line).
2. Route the page's load through `RemoteData` + `<app-async>` (typed via WP-06); wire the
   existing loading/empty/failure templates.
3. Update machine/store specs for the union transitions.
4. MDX page: the four states, `map2`/`andThen`, the delay-gated spinner, and the
   `?scenario=` dev toggle — linking `brief.page.ts` and `dashboard.page.ts` as live
   examples.

## Acceptance criteria

- [ ] No boolean-plus-error signal pairs in `brief/`.
- [ ] `/brief` renders all four async states (check with `?scenario=slow|empty|error`).
- [ ] Specs cover the transition union (Busy→Failed, Busy→Idle).
- [ ] MDX renders under Foundations.

## Verification

GREEN + `npm run test-storybook:ci`. Manual: `npm start` → `/brief` with
`?scenario=slow`, `?scenario=error`; exercise autosave + submit + rejection flow.

## Out of scope

Brief component stories (WP-15); machine renaming conventions (WP-08).

## Risks

Autosave (debounced) interplay with the new transition union — flush ordering must stay
as-is; the machine spec pins it.