# WP-27 — Brief UX layer (undo/redo, standaardbrief, search, diff badges)

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

## Why

PRD Brief v2 §7: the working-day features that make the composer pleasant daily.
Several are nearly free **because** state is one immutable value — that's the
teaching payload: undo/redo is a shell-side snapshot list, the rejection diff is a
pure function over two values. Say so in code comments and stories.

## Read first

- PRD Brief v2 §7 (and the plan-review trim recorded below)
- `src/app/brief/application/brief.store.ts` (autosave + `SaveState` already exist)
- `src/app/brief/domain/brief.machine.ts` — the `Seed` Msg (undo/redo's restore path)

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

- **Trim agreed at plan review.** IN: undo/redo, autosave retry affordance,
  standaardbrief, passage search, canvas zoom controls, Ctrl+Z/Ctrl+Shift+Z,
  block-level rejection-diff badges. OUT (deferred, one line each in Out of scope):
  soft lock/takeover, case-context panel, 401 autosave grace, per-user usage counts,
  shortcut-overlay dialog, inline character-level text diff.
- **Undo/redo is shell state, not machine state**: `past`/`future: Brief[]` in
  `BriefStore` (cap 50; push on `edit()`; clear `future` on a new edit); restore
  dispatches the **existing `Seed` Msg** — zero machine changes — then `scheduleSave()`.
- **Standaardbrief**: backend seeds `IsDefault` on 2–3 kern passages
  (`LibraryPassageDto` gains the flag); one button, visible only while the kern
  section is empty, dispatches the existing `PassagesInserted` with the default set —
  one Msg, one undo step.
- **Passage search is a client-side filter** in the picker (label + content match) —
  the library is small; no server search, no usage tracking.
- **Rejection diff**: pure `diffBlocks(before, after): BlockDiff[]` in
  `domain/brief-diff.ts` (added/removed/changed by `blockId`); the "before" snapshot
  is captured shell-side when the `Rejected` dispatch happens (POC limit: lost on
  reload — comment it). Rendered as "gewijzigd sinds afwijzing" badges on the canvas;
  the approver gets a "Toon wijzigingen" toggle on resubmission.
- **Autosave retry**: `SaveState.Error` already exists; add the "Opnieuw proberen"
  button that calls the existing flush path. No new state.

## Files

- `src/app/brief/application/brief.store.ts` (+spec: history bounds, clear-on-edit,
  redo, rejection snapshot)
- `src/app/brief/domain/brief-diff.ts` (new, +spec)
- `backend/src/BigRegister.Api/Data/BriefStore.cs` (`IsDefault` seed) +
  `Contracts/Dtos.cs` (`LibraryPassageDto`) + gen:api + adapter parse
- `src/app/brief/ui/passage-picker/*` (search input)
- `src/app/brief/ui/letter-canvas/*` (diff badges, standaardbrief button, zoom controls)
- `src/app/brief/ui/brief.page.ts` (undo/redo buttons + keydown listener, retry button)

## Steps

1. `diffBlocks` + spec (added/removed/changed/unchanged; changed = same blockId,
   different content).
2. Store: history + undo/redo + rejection snapshot (+spec).
3. Backend `IsDefault` + gen:api + parse.
4. UI: standaardbrief button, search, zoom, badges, keyboard, retry.
5. Stories for the new states (axe).

## Acceptance criteria

- [ ] Remove a block → Ctrl+Z restores it → Ctrl+Shift+Z re-removes; buttons mirror;
      history capped at 50; a new edit clears redo; restore re-triggers autosave.
- [ ] Empty kern + "Standaardbrief invoegen" → default passages inserted as one undo
      step; button gone once kern is non-empty.
- [ ] Search filters passages by label and content.
- [ ] Reject → edit → resubmit: approver toggles "Toon wijzigingen", changed/added/
      removed blocks are badged (block granularity).
- [ ] Autosave failure shows "Niet opgeslagen — opnieuw proberen"; retry works;
      content never lost locally.
- [ ] Full GREEN.

## Verification

GREEN one-liner; store + diff specs; manual reject→edit→diff walk with two roles.

## Out of scope (deferred, per plan review)

Soft lock/heartbeat/takeover (real session infra, no FP teaching value here).
Case-context panel (no case data exists). 401 autosave grace (auth is faked).
Per-user passage usage counts (bookkeeping, demos nothing). Shortcut overlay dialog
(no modal component exists; not worth building one). Inline character-level diff
(block granularity carries the teaching point).

## Risks

Undo history holds `Brief` snapshots — deep-frozen immutable values, so sharing is
safe, but never push non-content dispatches (status transitions, `Seed` itself) into
history or undo will replay workflow state. The rejection snapshot lives in memory
only — document it where it's captured.