feat(tag): hasAnyDocuments recursive helper + unit tests

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

frontend/src/lib/tag/tagUtils.test.ts

@@ -0,0 +1,29 @@
+import { describe, it, expect } from 'vitest';
+import { hasAnyDocuments } from './tagUtils';
+import type { components } from '$lib/generated/api';
+
+type TagTreeNodeDTO = components['schemas']['TagTreeNodeDTO'];
+
+function makeNode(documentCount: number, children: TagTreeNodeDTO[] = []): TagTreeNodeDTO {
+	return { id: 'id', name: 'name', documentCount, children };
+}
+
+describe('hasAnyDocuments', () => {
+	it('returns false for a leaf node with documentCount=0', () => {
+		expect(hasAnyDocuments(makeNode(0))).toBe(false);
+	});
+
+	it('returns true for a leaf node with documentCount=3', () => {
+		expect(hasAnyDocuments(makeNode(3))).toBe(true);
+	});
+
+	it('returns true for a root with documentCount=0 but a child with documentCount=5', () => {
+		const node = makeNode(0, [makeNode(5)]);
+		expect(hasAnyDocuments(node)).toBe(true);
+	});
+
+	it('returns false for a root with documentCount=0 and all children also 0', () => {
+		const node = makeNode(0, [makeNode(0), makeNode(0)]);
+		expect(hasAnyDocuments(node)).toBe(false);
+	});
+});

frontend/src/lib/tag/tagUtils.ts

@@ -0,0 +1,7 @@
+import type { components } from '$lib/generated/api';
+
+type TagTreeNodeDTO = components['schemas']['TagTreeNodeDTO'];
+
+export function hasAnyDocuments(node: TagTreeNodeDTO): boolean {
+	return (node.documentCount ?? 0) > 0 || (node.children ?? []).some(hasAnyDocuments);
+}