test(PersonMentionEditor): add placeholder show/hide behavior coverage

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

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

@@ -363,6 +363,38 @@ describe('PersonMentionEditor — XSS resistance', () => {
 	});
 });
 
+// ─── Placeholder behavior ─────────────────────────────────────────────────────
+
+describe('PersonMentionEditor — placeholder behavior', () => {
+	it('sets data-placeholder on the inner element when editor is empty', async () => {
+		render(PersonMentionEditorHost, {
+			initialValue: '',
+			initialMentions: [],
+			placeholder: 'Gib Text ein...',
+			onChange: () => {}
+		});
+		await vi.waitFor(() => {
+			const inner = document.querySelector('.tiptap-editor-inner') as HTMLElement | null;
+			expect(inner).not.toBeNull();
+			expect(inner!.getAttribute('data-placeholder')).toBe('Gib Text ein...');
+		});
+	});
+
+	it('omits data-placeholder on the inner element when editor has content', async () => {
+		render(PersonMentionEditorHost, {
+			initialValue: 'Bestehender Text',
+			initialMentions: [],
+			placeholder: 'Gib Text ein...',
+			onChange: () => {}
+		});
+		await vi.waitFor(() => {
+			const inner = document.querySelector('.tiptap-editor-inner') as HTMLElement | null;
+			expect(inner).not.toBeNull();
+			expect(inner!.hasAttribute('data-placeholder')).toBe(false);
+		});
+	});
+});
+
 // ─── Touch target (WCAG 2.2 AA) ──────────────────────────────────────────────
 
 describe('PersonMentionEditor — touch target', () => {