feat(fp): WP-27 — brief UX layer (undo/redo, standaardbrief, passage search, diff badges)

Brief letter-composition UX improvements:
- undo/redo history in the brief store (snapshot stacks, Ctrl/Cmd+Z) + retry-save
- "Standaardbrief invoegen" starter for empty sections; isDefault library passages
  (backend DTO/seed + adapter parse)
- passage-picker client-side search (rich-text textOf helper)
- rejection diff badges on the letter canvas + show/hide changes toggle
  (pure brief-diff domain fns + spec)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/brief/application/brief.store.spec.ts

@@ -1,7 +1,7 @@
 import { TestBed } from '@angular/core/testing';
 import { describe, it, expect, vi, afterEach } from 'vitest';
 import { Result } from '@shared/kernel/fp';
-import { Brief, BriefDecisions } from '@brief/domain/brief';
+import { Brief, BriefDecisions, LetterBlock } from '@brief/domain/brief';
 import { OrgTemplate } from '@brief/domain/org-template';
 import { BriefAdapter, BriefView } from '@brief/infrastructure/brief.adapter';
 import { LetterPreviewAdapter } from '@brief/infrastructure/letter-preview.adapter';
@@ -105,6 +105,104 @@ describe('BriefStore action state (Idle | Busy | Failed)', () => {
   });
 });
 
+// --- WP-27: undo/redo history + rejection diff ---
+
+function block(id: string, text: string): LetterBlock {
+  return { type: 'freeText', blockId: id, content: { paragraphs: [{ nodes: [{ type: 'text', text }] }] } };
+}
+const kern = (blocks: LetterBlock[]) => ({
+  sectionKey: 'kern',
+  title: 'Kern',
+  required: true,
+  locked: false,
+  blocks,
+});
+const filledBrief: Brief = { ...brief, sections: [kern([block('local-1', 'x')])] };
+const filledView: BriefView = { ...view, brief: filledBrief };
+
+function loadedBrief(store: BriefStore): Brief {
+  const s = store.model();
+  if (s.tag !== 'loaded') throw new Error('not loaded');
+  return s.brief;
+}
+
+async function loadedStore(over: Partial<BriefAdapter> = {}): Promise<BriefStore> {
+  const ok = (v: BriefView): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: v });
+  const store = setup({ load: () => ok(filledView), save: () => ok(filledView), ...over });
+  await store.load();
+  return store;
+}
+
+describe('BriefStore undo/redo history', () => {
+  it('records an edit, undoes and redoes it; buttons mirror; a no-op edit is not recorded', async () => {
+    const store = await loadedStore();
+    expect(store.canUndo()).toBe(false);
+
+    store.edit({ tag: 'BlockRemoved', blockId: 'local-1' });
+    expect(loadedBrief(store).sections[0].blocks.length).toBe(0);
+    expect(store.canUndo()).toBe(true);
+
+    store.undo();
+    expect(loadedBrief(store).sections[0].blocks.length).toBe(1);
+    expect(store.canRedo()).toBe(true);
+
+    store.redo();
+    expect(loadedBrief(store).sections[0].blocks.length).toBe(0);
+
+    // A no-op edit (unknown block) changes nothing → leaves no dead history step.
+    store.undo(); // back to 1 block, redo available
+    store.edit({ tag: 'BlockRemoved', blockId: 'does-not-exist' });
+    expect(store.canRedo()).toBe(true); // future NOT cleared by a no-op
+  });
+
+  it('a new edit clears the redo future', async () => {
+    const store = await loadedStore();
+    store.edit({ tag: 'FreeTextBlockAdded', sectionKey: 'kern' });
+    store.undo();
+    expect(store.canRedo()).toBe(true);
+    store.edit({ tag: 'FreeTextBlockAdded', sectionKey: 'kern' });
+    expect(store.canRedo()).toBe(false);
+  });
+
+  it('caps history at 50 snapshots', async () => {
+    const store = await loadedStore();
+    for (let i = 0; i < 55; i++) store.edit({ tag: 'FreeTextBlockAdded', sectionKey: 'kern' });
+    let undos = 0;
+    while (store.canUndo()) {
+      store.undo();
+      undos++;
+    }
+    expect(undos).toBe(50);
+  });
+});
+
+describe('BriefStore rejection diff', () => {
+  it('captures the rejected letter and diffs a subsequent edit against it', async () => {
+    const submitted: Brief = { ...filledBrief, status: { tag: 'submitted', submittedBy: 'u', submittedAt: 't' } };
+    const rejected: Brief = {
+      ...filledBrief,
+      status: { tag: 'rejected', rejectedBy: 'u2', rejectedAt: 't', comments: 'nee' },
+    };
+    const ok = (v: BriefView): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: v });
+    const store = setup({
+      load: () => ok({ ...filledView, brief: submitted }),
+      save: () => ok(filledView),
+      reject: () => ok({ ...filledView, brief: rejected }),
+    });
+    await store.load();
+    await store.reject('nee');
+    expect(store.hasRejectionDiff()).toBe(false); // nothing changed yet
+
+    store.edit({
+      tag: 'BlockContentEdited',
+      blockId: 'local-1',
+      content: { paragraphs: [{ nodes: [{ type: 'text', text: 'CHANGED' }] }] },
+    });
+    expect(store.blockDiffs().get('local-1')).toBe('changed');
+    expect(store.removedSinceReject()).toBe(0);
+  });
+});
+
 describe('BriefStore.previewLetter', () => {
   // vi.spyOn reuses an existing spy (and its call history) if one is already on
   // the property — window.open/URL.createObjectURL must be restored between tests.

src/app/brief/application/brief.store.ts

@@ -10,6 +10,7 @@ import {
   unresolvedPlaceholders,
 } from '@brief/domain/brief';
 import { BriefMsg, BriefState, initial, reduce } from '@brief/domain/brief.machine';
+import { BlockDiffKind, changedBlocks, diffBlocks } from '@brief/domain/brief-diff';
 import { OrgTemplate } from '@brief/domain/org-template';
 import { BriefAdapter, BriefView } from '@brief/infrastructure/brief.adapter';
 import { LetterPreviewAdapter } from '@brief/infrastructure/letter-preview.adapter';
@@ -52,6 +53,35 @@ export class BriefStore {
   /** Surfaced autosave state for the indicator + aria-live region. */
   readonly saveState = signal<SaveState>({ tag: 'Idle' });
 
+  /** Undo/redo is SHELL state, not machine state (WP-27): a stack of past/future
+      `Brief` snapshots. Each is a deep-frozen immutable value, so sharing is safe.
+      Only CONTENT edits are recorded (they flow through `edit()`); status transitions
+      never enter history, or undo would replay workflow state. Capped so a long session
+      can't grow unbounded. Restore re-dispatches the existing `Seed` Msg — zero machine
+      changes. */
+  private static readonly HISTORY_CAP = 50;
+  private past = signal<readonly Brief[]>([]);
+  private future = signal<readonly Brief[]>([]);
+  readonly canUndo = computed(() => this.past().length > 0);
+  readonly canRedo = computed(() => this.future().length > 0);
+
+  /** The letter as it stood when it was REJECTED, captured shell-side (WP-27). The
+      approver diffs it against the resubmitted letter. POC limit: in-memory only, so a
+      full page reload loses it — a real system would persist the rejected revision. */
+  private rejectionSnapshot = signal<Brief | null>(null);
+  /** Changed/added/removed blocks since rejection — a pure fold over two snapshots. */
+  readonly blockDiffs = computed<ReadonlyMap<string, BlockDiffKind>>(() => {
+    const before = this.rejectionSnapshot();
+    const after = this.brief();
+    return before && after ? changedBlocks(diffBlocks(before, after)) : new Map();
+  });
+  /** Count of blocks removed since rejection — badged as a summary, since a removed
+      block no longer renders inline. */
+  readonly removedSinceReject = computed(
+    () => [...this.blockDiffs().values()].filter((k) => k === 'removed').length,
+  );
+  readonly hasRejectionDiff = computed(() => this.blockDiffs().size > 0);
+
   /** The org template the letter renders with (WP-24). Server-owned appearance data,
       not letter state — held beside the machine, never inside it (`brief.machine.ts`
       stays untouched by design). Set from every server view that carries it. */
@@ -104,18 +134,50 @@ export class BriefStore {
     const r = await this.adapter.load();
     if (r.ok) {
       this.orgTemplate.set(r.value.orgTemplate);
+      this.clearHistory();
       this.store.dispatch({ tag: 'BriefLoaded', ...r.value });
     } else {
       this.store.dispatch({ tag: 'BriefLoadFailed', reason: r.error });
     }
   }
 
-  /** An edit: apply it optimistically in the pure reducer, then debounce-save. */
+  /** An edit: apply it optimistically in the pure reducer, then debounce-save. Records
+      an undo step only when the reducer actually changed the brief (a no-op edit — e.g.
+      a locked section — returns the same value and leaves no dead history step). */
   edit(msg: BriefMsg) {
+    const before = this.brief();
     this.store.dispatch(msg);
+    const after = this.brief();
+    if (before && after && after !== before) {
+      this.past.update((p) => [...p, before].slice(-BriefStore.HISTORY_CAP));
+      this.future.set([]);
+    }
     this.scheduleSave();
   }
 
+  /** Undo: restore the previous snapshot via the existing `Seed` Msg, push the current
+      onto the redo stack, then autosave. Redo is the mirror image. */
+  undo() {
+    this.step(this.past, this.future);
+  }
+  redo() {
+    this.step(this.future, this.past);
+  }
+  private step(from: typeof this.past, to: typeof this.future) {
+    const s = this.model();
+    const target = from().at(-1);
+    if (s.tag !== 'loaded' || !target) return;
+    from.update((x) => x.slice(0, -1));
+    to.update((x) => [...x, s.brief].slice(-BriefStore.HISTORY_CAP));
+    this.store.dispatch({ tag: 'Seed', state: { ...s, brief: target } });
+    this.scheduleSave();
+  }
+
+  private clearHistory() {
+    this.past.set([]);
+    this.future.set([]);
+  }
+
   private saveTimer?: ReturnType<typeof setTimeout>;
   private scheduleSave() {
     if (!this.canEdit()) return;
@@ -136,6 +198,11 @@ export class BriefStore {
     }
   }
 
+  /** Retry a failed autosave — reuses the existing flush path, no new state (WP-27). */
+  retrySave() {
+    void this.flushSave();
+  }
+
   /** Demo "start over": recreate the brief server-side and load the fresh view. */
   async resetDemo() {
     this.actionState.set({ tag: 'Busy' });
@@ -145,6 +212,8 @@ export class BriefStore {
     if (r.ok) {
       this.actionState.set({ tag: 'Idle' });
       this.orgTemplate.set(r.value.orgTemplate);
+      this.clearHistory();
+      this.rejectionSnapshot.set(null);
       this.store.dispatch({ tag: 'BriefLoaded', ...r.value });
     } else {
       this.actionState.set({ tag: 'Failed', error: r.error });
@@ -198,6 +267,9 @@ export class BriefStore {
         this.store.dispatch({ tag: 'Approved', by: s.approvedBy, at: s.approvedAt, decisions });
         break;
       case 'rejected':
+        // Capture the letter as-rejected for the resubmission diff (WP-27). This is the
+        // "before" snapshot the approver later compares against.
+        this.rejectionSnapshot.set(brief);
         this.store.dispatch({
           tag: 'Rejected',
           by: s.rejectedBy,

src/app/brief/domain/brief-diff.spec.ts

@@ -0,0 +1,41 @@
+import { describe, it, expect } from 'vitest';
+import { Brief, LetterBlock } from './brief';
+import { diffBlocks, changedBlocks } from './brief-diff';
+
+function block(id: string, text: string): LetterBlock {
+  return { type: 'freeText', blockId: id, content: { paragraphs: [{ nodes: [{ type: 'text', text }] }] } };
+}
+
+function brief(blocks: LetterBlock[]): Brief {
+  return {
+    briefId: 'b1',
+    beroep: 'arts',
+    templateId: 't1',
+    placeholders: [],
+    sections: [{ sectionKey: 'kern', title: 'Kern', required: true, locked: false, blocks }],
+    status: { tag: 'draft' },
+    drafterId: 'u1',
+  };
+}
+
+describe('diffBlocks', () => {
+  it('marks added, removed, changed and unchanged by blockId', () => {
+    const before = brief([block('local-1', 'a'), block('local-2', 'b'), block('local-3', 'c')]);
+    const after = brief([block('local-1', 'a'), block('local-2', 'B!'), block('local-4', 'd')]);
+    const diffs = diffBlocks(before, after);
+    const byId = new Map(diffs.map((d) => [d.blockId, d.kind]));
+    expect(byId.get('local-1')).toBe('unchanged');
+    expect(byId.get('local-2')).toBe('changed');
+    expect(byId.get('local-3')).toBe('removed'); // gone from after
+    expect(byId.get('local-4')).toBe('added'); // new in after
+  });
+
+  it('changedBlocks drops unchanged and keeps added/removed/changed', () => {
+    const before = brief([block('local-1', 'a'), block('local-2', 'b')]);
+    const after = brief([block('local-1', 'a'), block('local-2', 'B'), block('local-3', 'c')]);
+    const map = changedBlocks(diffBlocks(before, after));
+    expect(map.has('local-1')).toBe(false);
+    expect(map.get('local-2')).toBe('changed');
+    expect(map.get('local-3')).toBe('added');
+  });
+});

src/app/brief/domain/brief-diff.ts

@@ -0,0 +1,50 @@
+import { Brief, LetterBlock, allBlocks } from './brief';
+
+/**
+ * The rejection diff as a PURE function over two immutable `Brief` values — the whole
+ * teaching payload of WP-27: because state is one value, "what changed since the letter
+ * was rejected" is just a fold over two snapshots, no change-tracking bookkeeping.
+ *
+ * Blocks are matched by `blockId` (stable `local-N`/seed ids):
+ *  - in `after` but not `before` → `added`
+ *  - in `before` but not `after` → `removed`
+ *  - in both, different content   → `changed`
+ *  - in both, same content        → `unchanged`
+ */
+
+export type BlockDiffKind = 'added' | 'removed' | 'changed' | 'unchanged';
+
+export interface BlockDiff {
+  readonly blockId: string;
+  readonly kind: BlockDiffKind;
+}
+
+/** Content equality by value. Blocks are JSON-shaped immutable trees, so a canonical
+    stringify is an honest deep-equal here (no functions, no cycles). */
+function contentEqual(a: LetterBlock, b: LetterBlock): boolean {
+  return JSON.stringify(a.content) === JSON.stringify(b.content);
+}
+
+export function diffBlocks(before: Brief, after: Brief): BlockDiff[] {
+  const beforeById = new Map(allBlocks(before).map((b) => [b.blockId, b]));
+  const afterById = new Map(allBlocks(after).map((b) => [b.blockId, b]));
+  const out: BlockDiff[] = [];
+  for (const a of afterById.values()) {
+    const b = beforeById.get(a.blockId);
+    out.push({
+      blockId: a.blockId,
+      kind: !b ? 'added' : contentEqual(a, b) ? 'unchanged' : 'changed',
+    });
+  }
+  for (const b of beforeById.values()) {
+    if (!afterById.has(b.blockId)) out.push({ blockId: b.blockId, kind: 'removed' });
+  }
+  return out;
+}
+
+/** Lookup of only the blocks that changed since rejection (drops `unchanged`), for
+    badging the canvas. Keyed by `blockId`; removed ids are present too (the caller
+    surfaces them as a count — a removed block no longer renders inline). */
+export function changedBlocks(diffs: readonly BlockDiff[]): ReadonlyMap<string, BlockDiffKind> {
+  return new Map(diffs.filter((d) => d.kind !== 'unchanged').map((d) => [d.blockId, d.kind]));
+}

src/app/brief/domain/brief.ts

@@ -25,6 +25,7 @@ export interface LibraryPassage {
   readonly label: string;
   readonly content: RichTextBlock;
   readonly version: number; // library version, for provenance only
+  readonly isDefault?: boolean; // part of the "standaardbrief" (kern) starter set
 }
 
 /** A block inside a letter section: a frozen passage snapshot, or free text. */

src/app/brief/infrastructure/brief.adapter.ts

@@ -249,6 +249,7 @@ function parsePassage(dto: LibraryPassageDto): Result<string, LibraryPassage> {
     content: content.value,
     version: dto.version,
     ...(dto.beroep != null ? { beroep: dto.beroep } : {}),
+    ...(dto.isDefault ? { isDefault: true } : {}),
   });
 }
 

src/app/brief/ui/brief.page.ts

@@ -12,6 +12,7 @@ import { LetterComposerComponent } from '@brief/ui/letter-composer/letter-compos
 @Component({
   selector: 'app-brief-page',
   imports: [PageShellComponent, AlertComponent, ButtonComponent, ...ASYNC, LetterComposerComponent],
+  host: { '(document:keydown)': 'onKey($event)' },
   styles: [
     `
       .brief-toolbar {
@@ -21,6 +22,11 @@ import { LetterComposerComponent } from '@brief/ui/letter-composer/letter-compos
         gap: var(--rhc-space-max-md);
         margin-block-end: var(--rhc-space-max-lg);
       }
+      .toolbar-start {
+        display: flex;
+        align-items: center;
+        gap: var(--rhc-space-max-md);
+      }
       .save {
         color: var(--rhc-color-foreground-subtle);
         font-size: 0.9em;
@@ -42,7 +48,30 @@ import { LetterComposerComponent } from '@brief/ui/letter-composer/letter-compos
           @if (loaded(); as s) {
             @if (store.orgTemplate(); as orgTemplate) {
               <div class="brief-toolbar">
-                <span class="save" role="status" aria-live="polite">{{ saveText() }}</span>
+                <div class="toolbar-start">
+                  @if (store.canEdit()) {
+                    <app-button
+                      variant="subtle"
+                      [disabled]="!store.canUndo()"
+                      [attr.aria-label]="undoLabel"
+                      (click)="store.undo()"
+                      >{{ undoLabel }}</app-button
+                    >
+                    <app-button
+                      variant="subtle"
+                      [disabled]="!store.canRedo()"
+                      [attr.aria-label]="redoLabel"
+                      (click)="store.redo()"
+                      >{{ redoLabel }}</app-button
+                    >
+                  }
+                  <span class="save" role="status" aria-live="polite">{{ saveText() }}</span>
+                  @if (store.saveState().tag === 'Error') {
+                    <app-button variant="secondary" (click)="store.retrySave()">{{
+                      retrySaveLabel
+                    }}</app-button>
+                  }
+                </div>
                 <app-button variant="subtle" [disabled]="store.busy()" (click)="resetDemo()">{{
                   resetLabel
                 }}</app-button>
@@ -53,6 +82,8 @@ import { LetterComposerComponent } from '@brief/ui/letter-composer/letter-compos
                 [logoUrl]="store.logoUrl()"
                 [availablePassages]="s.availablePassages"
                 [diagnostics]="store.diagnostics()"
+                [blockDiffs]="store.blockDiffs()"
+                [removedCount]="store.removedSinceReject()"
                 [canEdit]="store.canEdit()"
                 [canApprove]="store.canApprove()"
                 [canReject]="store.canReject()"
@@ -83,10 +114,13 @@ export class BriefPage {
   protected failedText = $localize`:@@brief.page.failed:De brief kon niet worden geladen.`;
   protected retryText = $localize`:@@brief.page.retry:Opnieuw proberen`;
   protected resetLabel = $localize`:@@brief.page.reset:Opnieuw beginnen (demo)`;
+  protected undoLabel = $localize`:@@brief.page.undo:Ongedaan maken`;
+  protected redoLabel = $localize`:@@brief.page.redo:Opnieuw uitvoeren`;
+  protected retrySaveLabel = $localize`:@@brief.page.retrySave:Opnieuw proberen`;
 
   private savingText = $localize`:@@brief.page.saving:Concept opslaan…`;
   private savedText = $localize`:@@brief.page.saved:Concept opgeslagen`;
-  private saveErrorText = $localize`:@@brief.page.saveError:Opslaan mislukt`;
+  private saveErrorText = $localize`:@@brief.page.saveError:Niet opgeslagen — opnieuw proberen`;
 
   /** Debounced-save state, surfaced in a polite live region. */
   protected saveText = computed(() => {
@@ -121,4 +155,16 @@ export class BriefPage {
   protected reload() {
     void this.store.load();
   }
+
+  /** Ctrl/Cmd+Z = undo, Ctrl/Cmd+Shift+Z = redo (WP-27). Ignored while focus is in the
+      rich-text editor or a form control, so the browser's own text undo keeps working
+      there — our shell-level undo is for structural edits (add/remove/reorder blocks). */
+  protected onKey(e: KeyboardEvent) {
+    if (!(e.ctrlKey || e.metaKey) || e.key.toLowerCase() !== 'z' || !this.store.canEdit()) return;
+    const t = e.target as HTMLElement | null;
+    if (t && (t.isContentEditable || t.tagName === 'INPUT' || t.tagName === 'TEXTAREA')) return;
+    e.preventDefault();
+    if (e.shiftKey) this.store.redo();
+    else this.store.undo();
+  }
 }

src/app/brief/ui/letter-canvas/letter-canvas.component.ts

@@ -6,6 +6,7 @@ import {
   effect,
   inject,
   input,
+  linkedSignal,
   output,
   signal,
   viewChild,
@@ -21,6 +22,7 @@ import { OrgTemplate } from '@brief/domain/org-template';
 import { OrgTemplateTextField } from '@brief/domain/org-template.machine';
 import { Diagnostic } from '@brief/domain/placeholders';
 import { BriefMsg } from '@brief/domain/brief.machine';
+import { BlockDiffKind } from '@brief/domain/brief-diff';
 import { LetterSectionComponent } from '@brief/ui/letter-section/letter-section.component';
 
 /** A run of consecutive lines to render together: a list (bullet/number) or a single plain line. */
@@ -66,9 +68,40 @@ const A4_HEIGHT_PX = (297 * 96) / 25.4;
       }
       .toolbar {
         display: flex;
-        justify-content: flex-end;
+        justify-content: space-between;
+        align-items: center;
+        gap: var(--rhc-space-max-sm);
         margin-block-end: var(--rhc-space-max-sm);
       }
+      .zoom {
+        display: flex;
+        align-items: center;
+        gap: var(--rhc-space-max-sm);
+      }
+      .zoom-pct {
+        min-width: 3.5ch;
+        text-align: center;
+        color: var(--rhc-color-foreground-subtle);
+        font-variant-numeric: tabular-nums;
+      }
+      /* Rejection-diff badge (WP-27): a small pill above a changed/added block. */
+      .diff-block.diff-changed {
+        border-inline-start: 3px solid var(--rhc-color-oranje-500);
+        padding-inline-start: var(--rhc-space-max-sm);
+      }
+      .diff-badge {
+        display: inline-block;
+        margin-block-end: 1mm;
+        padding: 0 1.5mm;
+        border-radius: var(--rhc-border-radius-sm);
+        font-size: 7.5pt;
+        /* dark text, not white: oranje-500/groen-500 fail 4.5:1 contrast with white (WP-27 axe). */
+        color: var(--rhc-color-foreground-default);
+        background: var(--rhc-color-oranje-500);
+      }
+      .diff-badge.added {
+        background: var(--rhc-color-groen-500);
+      }
       /* Portal-side chrome around the letter surface (not part of the contract file). */
       .surface {
         background: var(--rhc-color-grijs-100);
@@ -139,20 +172,40 @@ const A4_HEIGHT_PX = (297 * 96) / 25.4;
       }
     </ng-template>
 
-    @if (editableRegions() === 'none') {
+    @if (editableRegions() !== 'template') {
       <div class="toolbar">
-        <app-button
-          variant="subtle"
-          (click)="showSample.set(!showSample())"
-          [attr.aria-pressed]="showSample()"
-        >
-          {{ showSample() ? hideSampleLabel() : showSampleLabel() }}
-        </app-button>
+        <div class="zoom" role="group" [attr.aria-label]="zoomGroupLabel()">
+          <app-button
+            variant="subtle"
+            [disabled]="zoomLevel() <= 0.5"
+            [attr.aria-label]="zoomOutLabel()"
+            (click)="zoomBy(-0.1)"
+            >−</app-button
+          >
+          <span class="zoom-pct">{{ zoomPct() }}</span>
+          <app-button
+            variant="subtle"
+            [disabled]="zoomLevel() >= 1.5"
+            [attr.aria-label]="zoomInLabel()"
+            (click)="zoomBy(0.1)"
+            >+</app-button
+          >
+          <app-button variant="subtle" (click)="zoomLevel.set(1)">{{ zoomResetLabel() }}</app-button>
+        </div>
+        @if (editableRegions() === 'none') {
+          <app-button
+            variant="subtle"
+            (click)="showSample.set(!showSample())"
+            [attr.aria-pressed]="showSample()"
+          >
+            {{ showSample() ? hideSampleLabel() : showSampleLabel() }}
+          </app-button>
+        }
       </div>
     }
 
     <div class="surface">
-      <div class="letter" #page [style]="marginStyle()" [style.zoom]="zoom()">
+      <div class="letter" #page [style]="marginStyle()" [style.zoom]="zoomLevel()">
         <!-- div, not <header>/<footer>: the CIBG huisstijl styles those bare elements
              (robijn footer background) — the letter surface must stay letter.css-only. -->
         <div class="letter__letterhead" [class.from-template]="tintTemplate()">
@@ -211,7 +264,14 @@ const A4_HEIGHT_PX = (297 * 96) / 25.4;
               <section>
                 <h3>{{ section.title }}</h3>
                 @for (block of section.blocks; track block.blockId) {
-                  @for (seg of segmentsOf(block); track $index) {
+                  @let diffKind = showDiff() ? blockDiffs().get(block.blockId) : undefined;
+                  <div class="diff-block" [class.diff-changed]="!!diffKind">
+                    @if (diffKind) {
+                      <span class="diff-badge" [class.added]="diffKind === 'added'">{{
+                        diffLabel(diffKind)
+                      }}</span>
+                    }
+                    @for (seg of segmentsOf(block); track $index) {
                     @if (seg.list === 'bullet') {
                       <ul>
                         @for (para of seg.items; track $index) {
@@ -242,7 +302,8 @@ const A4_HEIGHT_PX = (297 * 96) / 25.4;
                         />
                       </p>
                     }
-                  }
+                    }
+                  </div>
                 }
               </section>
             }
@@ -315,7 +376,13 @@ export class LetterCanvasComponent {
   availablePassages = input<readonly LibraryPassage[]>([]);
   placeholders = input<readonly PlaceholderOption[]>([]);
   diagnostics = input<readonly Diagnostic[]>([]);
+  /** Initial zoom; the in-canvas controls take over from here (WP-27). */
   zoom = input(1);
+  /** Blocks changed/added/removed since the letter was rejected (WP-27); badged when
+      `showDiff` is on. Removed blocks aren't in the map's rendered set — they no longer
+      exist in the letter — the composer surfaces them as a count. */
+  blockDiffs = input<ReadonlyMap<string, BlockDiffKind>>(new Map());
+  showDiff = input(false);
   /** The org logo's content URL (letterhead), or null when none is set. */
   logoUrl = input<string | null>(null);
   edit = output<BriefMsg>();
@@ -343,10 +410,26 @@ export class LetterCanvasComponent {
   signatureRoleLabel = input($localize`:@@brief.canvas.signatureRole:Functie ondertekenaar`);
   footerContactLabel = input($localize`:@@brief.canvas.footerContact:Contactgegevens (voettekst)`);
   footerLegalLabel = input($localize`:@@brief.canvas.footerLegal:Juridische voettekst`);
+  zoomGroupLabel = input($localize`:@@brief.canvas.zoom:Zoomniveau`);
+  zoomInLabel = input($localize`:@@brief.canvas.zoomIn:Inzoomen`);
+  zoomOutLabel = input($localize`:@@brief.canvas.zoomOut:Uitzoomen`);
+  zoomResetLabel = input($localize`:@@brief.canvas.zoomReset:100%`);
+  addedLabel = input($localize`:@@brief.diff.added:nieuw`);
+  changedLabel = input($localize`:@@brief.diff.changed:gewijzigd sinds afwijzing`);
 
   protected showSample = signal(false);
   protected letterDate = formatDatumNl(new Date());
 
+  /** Zoom seeded from the input; the +/−/reset controls drive it from there. */
+  protected zoomLevel = linkedSignal(() => this.zoom());
+  protected zoomPct = computed(() => `${Math.round(this.zoomLevel() * 100)}%`);
+  protected zoomBy(delta: number) {
+    // clamp 0.5–1.5; round to avoid float drift accumulating on repeated clicks.
+    this.zoomLevel.update((z) => Math.round(Math.min(1.5, Math.max(0.5, z + delta)) * 10) / 10);
+  }
+  protected diffLabel = (kind: BlockDiffKind) =>
+    kind === 'added' ? this.addedLabel() : this.changedLabel();
+
   /** The letterhead/signature/footer are tinted "not yours" only while composing —
       in 'none' the whole surface is read-only, in 'template' they ARE the editable focus. */
   protected tintTemplate = computed(() => this.editableRegions() === 'content');

src/app/brief/ui/letter-canvas/letter-canvas.stories.ts

@@ -148,6 +148,19 @@ export const TemplateMode: Story = { args: { editableRegions: 'template' } };
 
 export const Zoomed: Story = { args: { editableRegions: 'none', zoom: 0.6 } };
 
+/** Approver's "Toon wijzigingen": blocks changed/added since rejection are badged (WP-27). */
+export const WithDiff: Story = {
+  args: {
+    editableRegions: 'none',
+    diagnostics: [],
+    showDiff: true,
+    blockDiffs: new Map([
+      ['local-1', 'added'],
+      ['local-2', 'changed'],
+    ]),
+  },
+};
+
 /** Long letter: the approximate ±page-break marks appear per A4 interval. */
 export const PageBreak: Story = {
   args: { editableRegions: 'none', brief: longBrief, diagnostics: [] },

src/app/brief/ui/letter-composer/letter-composer.component.ts

@@ -1,4 +1,4 @@
-import { Component, computed, input, output } from '@angular/core';
+import { Component, computed, input, output, signal } from '@angular/core';
 import { HeadingComponent } from '@shared/ui/heading/heading.component';
 import { StatusBadgeComponent } from '@shared/ui/status-badge/status-badge.component';
 import { ButtonComponent } from '@shared/ui/button/button.component';
@@ -8,6 +8,7 @@ import { Brief, LibraryPassage } from '@brief/domain/brief';
 import { OrgTemplate } from '@brief/domain/org-template';
 import { Diagnostic } from '@brief/domain/placeholders';
 import { BriefMsg } from '@brief/domain/brief.machine';
+import { BlockDiffKind } from '@brief/domain/brief-diff';
 import { LetterCanvasComponent } from '@brief/ui/letter-canvas/letter-canvas.component';
 import { DiagnosticsPanelComponent } from '@brief/ui/diagnostics-panel/diagnostics-panel.component';
 import { RejectionCommentsComponent } from '@brief/ui/rejection-comments/rejection-comments.component';
@@ -62,6 +63,14 @@ import { RejectionCommentsComponent } from '@brief/ui/rejection-comments/rejecti
     <div class="head">
       <app-heading [level]="2">{{ title() }}</app-heading>
       <div class="head-end">
+        @if (hasRejectionDiff()) {
+          <app-button
+            variant="subtle"
+            [attr.aria-pressed]="showDiff()"
+            (click)="showDiff.set(!showDiff())"
+            >{{ showDiff() ? hideDiffLabel() : showDiffLabel() }}</app-button
+          >
+        }
         <app-button variant="subtle" [disabled]="busy()" (click)="preview.emit()">{{
           previewLabel()
         }}</app-button>
@@ -73,6 +82,10 @@ import { RejectionCommentsComponent } from '@brief/ui/rejection-comments/rejecti
       <app-rejection-comments mode="show" [comments]="rejectComments()" />
     }
 
+    @if (showDiff() && removedCount() > 0) {
+      <app-alert type="info">{{ removedText() }}</app-alert>
+    }
+
     <app-letter-canvas
       [brief]="brief()"
       [orgTemplate]="orgTemplate()"
@@ -81,6 +94,8 @@ import { RejectionCommentsComponent } from '@brief/ui/rejection-comments/rejecti
       [availablePassages]="availablePassages()"
       [placeholders]="menu()"
       [diagnostics]="diagnostics()"
+      [blockDiffs]="blockDiffs()"
+      [showDiff]="showDiff()"
       (edit)="edit.emit($event)"
     />
 
@@ -149,6 +164,12 @@ export class LetterComposerComponent {
   canSend = input(false);
   canSubmit = input(false);
   busy = input(false);
+  /** Rejection diff (WP-27): the changed/added/removed blocks and their count. The
+      "Toon wijzigingen" toggle only appears when there's something to show. */
+  blockDiffs = input<ReadonlyMap<string, BlockDiffKind>>(new Map());
+  removedCount = input(0);
+  protected hasRejectionDiff = computed(() => this.blockDiffs().size > 0);
+  protected showDiff = signal(false);
 
   edit = output<BriefMsg>();
   submit = output<void>();
@@ -160,6 +181,12 @@ export class LetterComposerComponent {
 
   title = input($localize`:@@brief.title:Brief aan de zorgverlener`);
   previewLabel = input($localize`:@@brief.preview.open:Voorbeeld`);
+  showDiffLabel = input($localize`:@@brief.diff.show:Toon wijzigingen`);
+  hideDiffLabel = input($localize`:@@brief.diff.hide:Verberg wijzigingen`);
+  removedText = computed(
+    () =>
+      $localize`:@@brief.diff.removed:${this.removedCount()}:count: blok(ken) verwijderd sinds afwijzing.`,
+  );
   submitLabel = input($localize`:@@brief.submit:Indienen ter beoordeling`);
   resubmitLabel = input($localize`:@@brief.resubmit:Opnieuw indienen`);
   submitHint = input(

src/app/brief/ui/letter-section/letter-section.component.ts

@@ -63,6 +63,11 @@ import { PassagePickerComponent } from '@brief/ui/passage-picker/passage-picker.
 
     @if (editable()) {
       <div class="actions">
+        @if (showStandardLetter()) {
+          <app-button variant="primary" (click)="insertStandardLetter()">{{
+            standardLetterLabel()
+          }}</app-button>
+        }
         <app-button variant="secondary" (click)="pickerOpen.set(!pickerOpen())">{{
           addPassageLabel()
         }}</app-button>
@@ -89,11 +94,27 @@ export class LetterSectionComponent {
   emptyLabel = input($localize`:@@brief.section.empty:Nog geen tekst in deze sectie.`);
   addPassageLabel = input($localize`:@@brief.section.addPassage:Standaardtekst toevoegen`);
   addFreeLabel = input($localize`:@@brief.section.addFree:Vrije tekst toevoegen`);
+  standardLetterLabel = input($localize`:@@brief.section.standardLetter:Standaardbrief invoegen`);
 
   protected pickerOpen = signal(false);
   protected sectionPassages = computed(() =>
     this.availablePassages().filter((p) => p.sectionKey === this.section().sectionKey),
   );
+  /** The "standaardbrief" starter set for this section (server-flagged defaults). */
+  protected defaultPassages = computed(() => this.sectionPassages().filter((p) => p.isDefault));
+  /** One-click starter, offered only while the section is still empty and defaults exist. */
+  protected showStandardLetter = computed(
+    () => this.section().blocks.length === 0 && this.defaultPassages().length > 0,
+  );
+
+  protected insertStandardLetter() {
+    // One Msg → one undo step (see brief.store `edit`).
+    this.edit.emit({
+      tag: 'PassagesInserted',
+      sectionKey: this.section().sectionKey,
+      passages: this.defaultPassages(),
+    });
+  }
 
   protected onContent(blockId: string, content: RichTextBlock) {
     this.edit.emit({ tag: 'BlockContentEdited', blockId, content });

src/app/brief/ui/letter-section/letter-section.stories.ts

@@ -36,6 +36,7 @@ const passages: LibraryPassage[] = [
     sectionKey: 'kern',
     label: 'Toelichting arts',
     version: 1,
+    isDefault: true, // part of the standaardbrief starter set (WP-27)
     content: { paragraphs: [{ nodes: [{ type: 'text', text: 'Als arts ...' }] }] },
   },
 ];
@@ -52,4 +53,5 @@ type Story = StoryObj<LetterSectionComponent>;
 
 export const ReadOnly: Story = { args: { editable: false } };
 export const Editable: Story = { args: { editable: true } };
+/** Empty section: the one-click "Standaardbrief invoegen" starter appears (WP-27). */
 export const EditableEmpty: Story = { args: { section: emptySection, editable: true } };

src/app/brief/ui/passage-picker/passage-picker.component.ts

@@ -1,7 +1,9 @@
-import { Component, input, output, signal } from '@angular/core';
+import { Component, computed, input, output, signal } from '@angular/core';
 import { FormsModule } from '@angular/forms';
 import { CheckboxComponent } from '@shared/ui/checkbox/checkbox.component';
 import { ButtonComponent } from '@shared/ui/button/button.component';
+import { TextInputComponent } from '@shared/ui/text-input/text-input.component';
+import { textOf } from '@shared/kernel/rich-text';
 import { LibraryPassage } from '@brief/domain/brief';
 
 /** Molecule: multi-select list of the section's library passages. One "Voeg toe"
@@ -9,7 +11,7 @@ import { LibraryPassage } from '@brief/domain/brief';
     single-insert path. Presentational: emits the chosen passages in list order. */
 @Component({
   selector: 'app-passage-picker',
-  imports: [FormsModule, CheckboxComponent, ButtonComponent],
+  imports: [FormsModule, CheckboxComponent, ButtonComponent, TextInputComponent],
   styles: [
     `
       :host {
@@ -19,6 +21,9 @@ import { LibraryPassage } from '@brief/domain/brief';
         border-radius: var(--rhc-border-radius-md);
         padding: var(--rhc-space-max-md);
       }
+      .search {
+        margin-block-end: var(--rhc-space-max-md);
+      }
       ul {
         list-style: none;
         margin: 0 0 var(--rhc-space-max-md);
@@ -29,11 +34,24 @@ import { LibraryPassage } from '@brief/domain/brief';
       .scope {
         color: var(--rhc-color-foreground-subtle);
       }
+      .empty {
+        color: var(--rhc-color-foreground-subtle);
+        font-style: italic;
+        margin: 0 0 var(--rhc-space-max-md);
+      }
     `,
   ],
   template: `
+    <div class="search">
+      <app-text-input
+        [placeholder]="searchLabel()"
+        [attr.aria-label]="searchLabel()"
+        [ngModel]="query()"
+        (ngModelChange)="query.set($event)"
+      />
+    </div>
     <ul>
-      @for (p of passages(); track p.passageId) {
+      @for (p of filtered(); track p.passageId) {
         <li>
           <app-checkbox
             [checkboxId]="'passage-' + p.passageId"
@@ -43,6 +61,8 @@ import { LibraryPassage } from '@brief/domain/brief';
           />
           <span class="scope"> · {{ p.scope === 'beroep' ? beroepLabel() : globalLabel() }}</span>
         </li>
+      } @empty {
+        <li class="empty">{{ noMatchLabel() }}</li>
       }
     </ul>
     <app-button variant="secondary" [disabled]="count() === 0" (click)="add()"
@@ -57,8 +77,20 @@ export class PassagePickerComponent {
   addLabel = input($localize`:@@brief.picker.add:Voeg toe`);
   globalLabel = input($localize`:@@brief.picker.global:algemeen`);
   beroepLabel = input($localize`:@@brief.picker.beroep:beroepsspecifiek`);
+  searchLabel = input($localize`:@@brief.picker.search:Zoek in standaardteksten…`);
+  noMatchLabel = input($localize`:@@brief.picker.noMatch:Geen standaardteksten gevonden.`);
 
   protected checked = signal<Record<string, boolean>>({});
+  protected query = signal('');
+  /** Client-side filter on label + rendered content text — the library is small, so no
+      server search (WP-27). Placeholder keys are searchable too (see `textOf`). */
+  protected filtered = computed(() => {
+    const q = this.query().trim().toLowerCase();
+    if (!q) return this.passages();
+    return this.passages().filter(
+      (p) => p.label.toLowerCase().includes(q) || textOf(p.content).includes(q),
+    );
+  });
   protected count = () => Object.values(this.checked()).filter(Boolean).length;
 
   protected set(id: string, on: boolean) {

src/app/shared/infrastructure/api-client.ts

@@ -1712,6 +1712,7 @@ export interface LibraryPassageDto {
     content?: RichTextBlockDto;
     version?: number;
     beroep?: string | undefined;
+    isDefault?: boolean;
 }
 
 export interface ManualDiplomaPolicyDto {

src/app/shared/kernel/rich-text.ts

@@ -49,6 +49,15 @@ export function deepCopyBlock(block: RichTextBlock): RichTextBlock {
   return structuredClone(block) as RichTextBlock;
 }
 
+/** All visible text of a block as one lowercased string — for client-side search over
+    passages. Placeholders contribute their key so "naam" matches a `naam_zorgverlener` chip. */
+export function textOf(block: RichTextBlock): string {
+  return block.paragraphs
+    .flatMap((p) => p.nodes.map((n) => (n.type === 'text' ? n.text : n.type === 'placeholder' ? n.key : '')))
+    .join(' ')
+    .toLowerCase();
+}
+
 /** Every placeholder key used in a block, in document order (duplicates kept — the
     caller dedupes when it wants a set). */
 export function placeholderKeysIn(block: RichTextBlock): string[] {