feat: render OneNote notebook hierarchy

src/components/SectionNavigation.test.tsx

@@ -0,0 +1,46 @@
+import { describe, expect, it } from 'vitest';
+
+import type { OneNotePageSummaryDto } from '../onenote/model/dto.js';
+import { buildPageTree } from './page-tree.js';
+
+function page(id: string, level?: number): OneNotePageSummaryDto {
+  return { id, level, title: id, text: '', textPreview: '' };
+}
+
+describe('section navigation trees', () => {
+  it('turns authored page levels into parent/subpage relationships', () => {
+    expect(
+      buildPageTree([
+        page('root', 1),
+        page('child', 2),
+        page('grandchild', 3),
+        page('next-root', 1),
+        page('skipped-level', 3),
+      ])
+    ).toEqual([
+      {
+        page: page('root', 1),
+        children: [
+          {
+            page: page('child', 2),
+            children: [{ page: page('grandchild', 3), children: [] }],
+          },
+        ],
+      },
+      {
+        page: page('next-root', 1),
+        children: [{ page: page('skipped-level', 3), children: [] }],
+      },
+    ]);
+  });
+
+  it('treats absent and invalid levels as top-level pages', () => {
+    expect(
+      buildPageTree([page('unset'), page('zero', 0), page('nan', Number.NaN)])
+    ).toMatchObject([
+      { page: { id: 'unset' }, children: [] },
+      { page: { id: 'zero' }, children: [] },
+      { page: { id: 'nan' }, children: [] },
+    ]);
+  });
+});