Exercise 1: The Parent Picker — Possible Solution
====================================================================

// src/pages/api/pages/candidates.ts
export const GET: APIRoute = async ({ url }) => {
  const excludeId = Number(url.searchParams.get('exclude'));
  const candidates = await db
    .select({ id: pages.id, fullPath: pages.fullPath })
    .from(pages)
    .where(ne(pages.id, excludeId));

  return new Response(JSON.stringify(candidates), {
    headers: { 'Content-Type': 'application/json' },
  });
};

// admin page (excerpt) - a plain <input> filtering a <select>
<input id="filter" placeholder="Search pages..." />
<select id="parent-select">
  {candidates.map((c) => <option value={c.id}>{c.fullPath}</option>)}
</select>

<script>
  document.getElementById('filter').addEventListener('input', (e) => {
    const query = e.target.value.toLowerCase();
    document.querySelectorAll('#parent-select option').forEach((opt) => {
      opt.hidden = !opt.textContent.toLowerCase().includes(query);
    });
  });
</script>

WHY THIS WORKS AS AN ANSWER
------------------------------
It correctly excludes the page being edited from its own candidate
list via ne(pages.id, excludeId) - reparenting a page under itself
would corrupt the tree - and correctly implements simple client-side
filtering over the resulting flat list, matching the same
searchable-flat-list convention every sibling course already used.