test(person-mention): assert popup degrades to empty state on fetch reject

Tester #5506 §4: there was a test for fetch returning ok:false but no
test for the broad catch covering thrown rejections (DNS failure,
TypeError: Failed to fetch). Pin that path so a future refactor can't
accidentally bubble the error and crash the editor.

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

frontend/src/lib/components/PersonMentionEditor.svelte.spec.ts

@@ -52,6 +52,12 @@ function mockFetchEmpty() {
 	return fetchMock;
 }
 
+function mockFetchRejects() {
+	const fetchMock = vi.fn().mockRejectedValue(new TypeError('Failed to fetch'));
+	vi.stubGlobal('fetch', fetchMock);
+	return fetchMock;
+}
+
 function getTextarea(): HTMLTextAreaElement {
 	return document.querySelector('textarea')!;
 }
@@ -182,6 +188,21 @@ describe('PersonMentionEditor — typeahead', () => {
 		await expect.element(page.getByText('Keine Personen gefunden')).toBeInTheDocument();
 	});
 
+	it('falls back to the empty state when the typeahead fetch rejects (network error)', async () => {
+		mockFetchRejects();
+		renderHost();
+
+		const ta = getTextarea();
+		ta.focus();
+		ta.value = '@Aug';
+		ta.selectionStart = 4;
+		ta.selectionEnd = 4;
+		ta.dispatchEvent(new Event('input', { bubbles: true }));
+		await flushDebounce();
+
+		await expect.element(page.getByText('Keine Personen gefunden')).toBeInTheDocument();
+	});
+
 	it('keeps the popup open when the query has a trailing space (multi-word names)', async () => {
 		mockFetchWithPersons();
 		renderHost();