Implement Idempotent Order Creation

Prevent duplicate addresses for the same order:

async function getOrCreatePaymentAddress(orderId, options) {
  const order = await db.orders.get(orderId);

  // Return existing address if already created
  if (order.walletId) {
    const wallet = await waas.getWallet(order.walletId);
    return wallet.wallet;
  }

  // Create new address
  const result = await waas.createWallet({
    network: options.network,
    crypto: options.crypto,
    metadata: { orderId },
    expiresInMinutes: options.expiresInMinutes,
  });

  // Store wallet ID atomically
  await db.orders.update(orderId, {
    walletId: result.wallet.id,
    depositAddress: result.wallet.address,
  });

  return result.wallet;
}