# WP-24 — Letter canvas (edit on the letter)

Status: done
Phase: 6 — Brief v2 (edit-on-the-letter, org templates, server-rendered preview)

## Why

The drafter should compose **on the letter** — letterhead above, footer/signature
below, content blocks edited in place — instead of in an abstract form next to a
separate preview. PRD Brief v2 §4. This is a **presentation rebuild only**: the
domain model, `brief.machine.ts`, and every `BriefMsg` stay byte-identical.

## Read first

- PRD Brief v2 §2b (fidelity note), §4, §10; the sample `voorbeeldbrief-inschrijving.pdf`
- `src/app/brief/ui/letter-composer/letter-composer.component.ts` (the `canEdit` pivot)
- `src/app/brief/ui/letter-preview/letter-preview.component.ts` (rendering that migrates in)
- `docs/backlog/WP-23-org-template-backend.md` (the `orgTemplate` on `BriefViewDto`)

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

- **One stylesheet is the FE⇄BE rendering contract**: `public/letter.css` — class
  vocabulary `.letter`, `.letter__letterhead`, `.letter__body`, `.letter__signature`,
  `.letter__footer`, `.letter__page-break`; margins as `--letter-margin-*` custom
  props; `@page`/print rules. Loaded via `<link>` in `index.html` (app + Storybook).
  WP-25's backend renderer inlines the same file; its parity test is the fence.
- **`LetterCanvasComponent`** (new organism, `Domein/Brief/Letter Canvas`) with
  `editableRegions: 'content' | 'template' | 'none'` — one component serves drafter
  composing, approver review (and in WP-26, the admin editor). Letter typography on
  the canvas is the letter's, not the portal UI's — but still token-bridged.
- `'content'` mode hosts the **existing** `letter-section`/`letter-block` components
  unchanged; letterhead/footer/signature render read-only with a subtle tint and a
  first-use caption ("komt uit de huisstijl van de organisatie").
- `'none'` mode absorbs `letter-preview`'s rendering (paragraph grouping, placeholder
  chips, sample-values toggle); **`ui/letter-preview/` is then deleted** — the PRD
  explicitly supersedes it; no third rendering is maintained.
- **Page-break indicator is approximate by design**: a dashed line per A4-content
  interval with the caption "±pagina-einde — afdrukvoorbeeld is leidend" (PRD §2b
  honesty requirement).
- `brief.machine.ts` and `BriefMsg` are untouched — `git diff` must prove it.

## Files

- `public/letter.css` (new), `src/index.html` (link)
- `src/app/brief/domain/org-template.ts` (new, pure) — `OrgTemplate` type
- `src/app/brief/infrastructure/brief.adapter.ts` (+spec) — parse `orgTemplate`
- `src/app/brief/ui/letter-canvas/*` (new: component + stories)
- `src/app/brief/ui/letter-composer/letter-composer.component.ts` (pivot swap) + stories
- `src/app/brief/ui/brief.page.ts` (pass orgTemplate through)
- delete `src/app/brief/ui/letter-preview/*`

## Steps

1. `letter.css` from the sample PDF's geometry (A4 proportions, letterhead, address
   window + reference block, footer rule, signature).
2. `OrgTemplate` domain type + `parseOrgTemplate` boundary in the adapter (+spec).
3. Canvas organism: three modes, zoom input, page-break indicator.
4. Migrate `letter-preview` rendering into `'none'` mode; delete the component,
   fold its stories into the canvas stories.
5. Swap the composer's `@if (canEdit())` pivot for
   `<app-letter-canvas [editableRegions]="canEdit() ? 'content' : 'none'">`.
6. Stories: three modes + zoom + page-break, all axe-gated.

## Acceptance criteria

- [x] Drafter edits blocks in place on the letter surface; passage picker and
      diagnostics click-to-locate still work on the canvas.
- [x] Approver sees the identical surface read-only with the action bar.
- [x] Letterhead/footer/signature come from `orgTemplate` and are visibly non-editable.
- [x] `git diff` shows zero changes in `brief.machine.ts` / `brief.ts` Msg surface.
- [x] `letter-preview` is gone; no story regression (`test-storybook:ci` green).
- [x] Full GREEN + e2e smoke.

Field notes (landed alongside): the CIBG huisstijl styles bare `<header>`/`<footer>`
elements (robijn background), so the canvas regions are `<div>`s — the letter surface
must stay letter.css-only. The passage picker's checkboxes now get unique
`checkboxId`s (all previously resolved to `id="undefined"`, so labels toggled only
the first box — multi-select was broken) and an opaque background; `.letter__body`
stacks above the page-break marks so the dashed line never draws through content,
while the "±pagina-einde" caption floats above everything for legibility.

## Verification

GREEN one-liner; `npm run e2e` (brief flow); manual: `?role=drafter` compose on
canvas, `?role=approver` review; `?scenario=slow|error` still degrade gracefully
through `<app-async>`.

## Out of scope

Server-rendered preview + `[NOG IN TE VULLEN]` resolution (WP-25); admin `'template'`
mode wiring beyond the input existing (WP-26 gives it a consumer); zoom controls
polish + standaardbrief + diff badges (WP-27).

## Risks

The canvas duplicates the letter markup that WP-25's backend renderer will emit —
acceptable *only* because `letter.css` is shared and WP-25 adds the class-parity
test; until WP-25 lands, the canvas is the sole consumer, so no drift is possible.
Deleting `letter-preview` breaks any deep import of it — repo-wide grep before delete.