test(briefwechsel): cover the index page branches

Hero state when no senderId set, results card when senderId set,
SinglePersonHintBar gating on senderId × !receiverId, empty-results
message branch.

5 tests covering ~15 branches in the orchestrator.

Refs #496.

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

frontend/src/routes/briefwechsel/page.svelte.test.ts

@@ -0,0 +1,93 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+
+vi.mock('$app/navigation', () => ({
+	beforeNavigate: () => {},
+	afterNavigate: () => {},
+	goto: vi.fn(),
+	invalidate: vi.fn(),
+	invalidateAll: vi.fn(),
+	preloadCode: vi.fn(),
+	preloadData: vi.fn(),
+	pushState: vi.fn(),
+	replaceState: vi.fn(),
+	disableScrollHandling: vi.fn(),
+	onNavigate: () => () => {}
+}));
+
+const { default: BriefwechselPage } = await import('./+page.svelte');
+
+afterEach(cleanup);
+
+const baseData = (overrides: Record<string, unknown> = {}) => ({
+	filters: { senderId: '', receiverId: '', from: '', to: '', dir: 'DESC' },
+	initialValues: { senderName: '', receiverName: '' },
+	documents: [],
+	canWrite: false,
+	...overrides
+});
+
+describe('briefwechsel/+ page', () => {
+	it('renders the hero when no senderId is set', async () => {
+		render(BriefwechselPage, { props: { data: baseData() } });
+
+		// CorrespondenzHero should render
+		const inputs = document.querySelectorAll('input');
+		expect(inputs.length).toBeGreaterThan(0);
+	});
+
+	it('renders the results card when a senderId is set', async () => {
+		render(BriefwechselPage, {
+			props: {
+				data: baseData({
+					filters: { senderId: 'p1', receiverId: '', from: '', to: '', dir: 'DESC' },
+					initialValues: { senderName: 'Anna Schmidt', receiverName: '' }
+				})
+			}
+		});
+
+		// CorrespondenzPersonBar should render with results context
+		await expect.element(page.getByText(/Anna Schmidt/)).toBeVisible();
+	});
+
+	it('renders the SinglePersonHintBar when there is a sender but no receiver', async () => {
+		render(BriefwechselPage, {
+			props: {
+				data: baseData({
+					filters: { senderId: 'p1', receiverId: '', from: '', to: '', dir: 'DESC' },
+					initialValues: { senderName: 'Anna', receiverName: '' }
+				})
+			}
+		});
+
+		// "Alle Briefe von Anna" message from SinglePersonHintBar
+		await expect.element(page.getByText(/wähle einen korrespondenten/i)).toBeVisible();
+	});
+
+	it('renders the empty results message when documents is empty and a sender is set', async () => {
+		render(BriefwechselPage, {
+			props: {
+				data: baseData({
+					filters: { senderId: 'p1', receiverId: '', from: '', to: '', dir: 'DESC' },
+					initialValues: { senderName: 'Anna', receiverName: '' }
+				})
+			}
+		});
+
+		await expect.element(page.getByText('Keine Dokumente gefunden.')).toBeVisible();
+	});
+
+	it('hides the SinglePersonHintBar when both sender and receiver are set', async () => {
+		render(BriefwechselPage, {
+			props: {
+				data: baseData({
+					filters: { senderId: 'p1', receiverId: 'p2', from: '', to: '', dir: 'DESC' },
+					initialValues: { senderName: 'Anna', receiverName: 'Bert' }
+				})
+			}
+		});
+
+		await expect.element(page.getByText(/wähle einen korrespondenten/i)).not.toBeInTheDocument();
+	});
+});