feat(persons): add sort toggle to person document list (issue #24)

Extracted sortDocumentsByDate utility with full Vitest coverage (6 tests),
wired it into the person detail page with a DESC/ASC toggle button, and
added an E2E smoke test for the toggle interaction.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/e2e/persons.spec.ts

@@ -72,6 +72,25 @@ test.describe('New person', () => {
 	});
 });
 
+test.describe('Person detail — sort toggle', () => {
+	test('sort toggle changes the button label when person has documents', async ({ page }) => {
+		await page.goto('/persons');
+		const firstPerson = page.locator('a[href^="/persons/"]').first();
+		await firstPerson.click();
+		await page.waitForSelector('[data-hydrated]');
+
+		const sortBtn = page.getByRole('button', { name: /Neueste zuerst|Älteste zuerst/i });
+		if (await sortBtn.isVisible()) {
+			await expect(sortBtn).toContainText('Neueste zuerst');
+			await sortBtn.click();
+			await expect(sortBtn).toContainText('Älteste zuerst');
+			await sortBtn.click();
+			await expect(sortBtn).toContainText('Neueste zuerst');
+			await page.screenshot({ path: 'test-results/e2e/person-sort-toggle.png' });
+		}
+	});
+});
+
 test.describe('Conversations', () => {
 	test('shows the empty state when no persons are selected', async ({ page }) => {
 		await page.goto('/conversations');

frontend/src/lib/utils/sort.spec.ts

@@ -0,0 +1,44 @@
+import { describe, expect, it } from 'vitest';
+import { sortDocumentsByDate } from './sort';
+
+const doc = (id: string, documentDate: string | null) =>
+	({ id, documentDate } as { id: string; documentDate: string | null });
+
+describe('sortDocumentsByDate', () => {
+	it('sorts DESC by default — newest first', () => {
+		const docs = [doc('a', '1920-01-01'), doc('b', '1950-06-15'), doc('c', '1935-03-10')];
+		const result = sortDocumentsByDate(docs, 'DESC');
+		expect(result.map((d) => d.id)).toEqual(['b', 'c', 'a']);
+	});
+
+	it('sorts ASC — oldest first', () => {
+		const docs = [doc('a', '1920-01-01'), doc('b', '1950-06-15'), doc('c', '1935-03-10')];
+		const result = sortDocumentsByDate(docs, 'ASC');
+		expect(result.map((d) => d.id)).toEqual(['a', 'c', 'b']);
+	});
+
+	it('places documents without a date last in DESC', () => {
+		const docs = [doc('a', null), doc('b', '1940-01-01'), doc('c', null)];
+		const result = sortDocumentsByDate(docs, 'DESC');
+		expect(result[0].id).toBe('b');
+		expect(result.slice(1).map((d) => d.id)).toContain('a');
+		expect(result.slice(1).map((d) => d.id)).toContain('c');
+	});
+
+	it('places documents without a date last in ASC', () => {
+		const docs = [doc('a', null), doc('b', '1940-01-01'), doc('c', null)];
+		const result = sortDocumentsByDate(docs, 'ASC');
+		expect(result[0].id).toBe('b');
+	});
+
+	it('does not mutate the original array', () => {
+		const docs = [doc('a', '1950-01-01'), doc('b', '1920-01-01')];
+		const original = [...docs];
+		sortDocumentsByDate(docs, 'ASC');
+		expect(docs).toEqual(original);
+	});
+
+	it('returns an empty array unchanged', () => {
+		expect(sortDocumentsByDate([], 'DESC')).toEqual([]);
+	});
+});

frontend/src/lib/utils/sort.ts

@@ -0,0 +1,19 @@
+export type SortDir = 'ASC' | 'DESC';
+
+/**
+ * Returns a new array of documents sorted by documentDate.
+ * Documents without a date are always placed last, regardless of direction.
+ */
+export function sortDocumentsByDate<T extends { documentDate?: string | null }>(
+	docs: T[],
+	dir: SortDir
+): T[] {
+	return [...docs].sort((a, b) => {
+		const da = a.documentDate ?? '';
+		const db = b.documentDate ?? '';
+		if (!da && !db) return 0;
+		if (!da) return 1;
+		if (!db) return -1;
+		return dir === 'DESC' ? db.localeCompare(da) : da.localeCompare(db);
+	});
+}

frontend/src/routes/persons/[id]/+page.svelte

@@ -2,12 +2,16 @@
     import { enhance } from '$app/forms';
     import PersonTypeahead from '$lib/components/PersonTypeahead.svelte';
     import { m } from '$lib/paraglide/messages.js';
+    import { sortDocumentsByDate, type SortDir } from '$lib/utils/sort';
 
     let { data, form } = $props();
 
     const person = $derived(data.person);
     const documents = $derived(data.documents);
 
+    let sortDir = $state<SortDir>('DESC');
+    const sortedDocuments = $derived(sortDocumentsByDate(documents, sortDir));
+
     let editMode = $state(false);
     let mergeTargetId = $state('');
     let showMergeConfirm = $state(false);
@@ -200,10 +204,21 @@
     <!-- Linked Documents Section -->
     <div>
         <div class="flex items-center justify-between mb-6 border-b border-brand-navy/10 pb-2">
-            <h2 class="text-xl font-serif text-brand-navy">{m.person_docs_heading()}</h2>
-            <span class="bg-brand-navy text-white text-xs font-bold px-2 py-1 rounded-full">
-                {documents.length}
-            </span>
+            <div class="flex items-center gap-3">
+                <h2 class="text-xl font-serif text-brand-navy">{m.person_docs_heading()}</h2>
+                <span class="bg-brand-navy text-white text-xs font-bold px-2 py-1 rounded-full">
+                    {documents.length}
+                </span>
+            </div>
+            {#if documents.length > 0}
+                <button
+                    onclick={() => (sortDir = sortDir === 'DESC' ? 'ASC' : 'DESC')}
+                    class="text-xs font-bold uppercase tracking-widest text-gray-400 hover:text-brand-navy transition-colors"
+                    aria-label={m.conv_sort_label()}
+                >
+                    {sortDir === 'DESC' ? m.conv_sort_newest() : m.conv_sort_oldest()}
+                </button>
+            {/if}
         </div>
 
         {#if documents.length === 0}
@@ -212,7 +227,7 @@
             </div>
         {:else}
             <ul class="space-y-3">
-                {#each documents as doc}
+                {#each sortedDocuments as doc}
                     <li class="group">
                         <a href="/documents/{doc.id}" class="block bg-white border border-brand-sand p-4 hover:border-brand-navy hover:shadow-md transition-all duration-200">
                             <div class="flex items-center justify-between">