export async function onRequestPost({ request, env }) {
  try {
    const { username, pass_hash } = await request.json();
    if (!username || !pass_hash) return new Response('Missing fields', { status: 400 });
    if (await env.D1_EV.prepare("SELECT 1 FROM users WHERE username = ?").bind(username).first())
      return new Response('User already exists', { status: 409 });
    await env.D1_EV.prepare("INSERT INTO users (username, pass_hash) VALUES (?, ?)")
      .bind(username, pass_hash).run();
    return Response.json({ success: true, username }, { status: 201 });
  } catch (e) { return new Response(e.message, { status: 500 }); }
}