Pay native USDC on Arc

// Pays USDC on Arc as native value. Arc's gas coin is USDC: the native balance has 18 decimals and
// the ERC-20 `USDC` has 6, and both read one balance. The program reads the Pot's native balance
// (`pot.balance`) and its token balance (`pot.USDC`), requires the token reading to equal the native
// reading divided by 10^12, sends `amountNative` to `to` with `evm.call`, and measures what `to`
// received at both scales. The cook reverts, and nothing moves, when `amountNative` is zero or not
// a whole number of USDC base units (a multiple of 10^12), when `to` is the zero address or the
// Pot, when the Pot holds less, when the two readings disagree, or when `to` receives a different
// amount.
//
//   sauce simulate arc-native-payment.sauce.ts --chain arc --owner <address> \
//     --assume-balance USDC:<whole-tokens> --args <amountNative> <to>
//   sauce run arc-native-payment.sauce.ts --chain arc --wallet <name> --args <amountNative> <to>
//
//   amountNative: Uint256  the USDC to pay as native value, in 18 decimals:
//                          1000000000000000000 is 1 USDC; a multiple of 10^12
//   to: Address            who is paid
//
// On Arc, pay 1.5 USDC to 0x2154…676d:
//
//   sauce run arc-native-payment.sauce.ts --chain arc --wallet me \
//     --args 1500000000000000000 0x21543327A3f4282A3649a7b1AAe499fdCaB3676d
function main(
  amountNative: Uint256,
  to: Address,
): {
  potNative: Uint256;
  potUsdc: Uint256;
  receivedNative: Uint256;
  receivedUsdc: Uint256;
} {
  const scale = 10 ** 12;
  require(amountNative > 0, "amountNative is zero");
  require(amountNative % scale == 0, "amountNative is not a whole number of USDC base units");
  require(to != 0 && to != pot, "to is the zero address or the Pot");

  // One balance, two readings: 18 decimals natively, 6 through the token.
  const potNative = pot.balance;
  const potUsdc = pot.USDC;
  require(potUsdc == potNative / scale, "the native and token readings disagree");
  require(potNative >= amountNative, "not enough USDC in the Pot");

  // Pay as native value: evm.call is the only call that sends value; empty calldata.
  const empty = hex``;
  const nativeBefore = ctx.balance(to);
  const usdcBefore = USDC.balanceOf(to);
  evm.call(to, amountNative, empty);
  const receivedNative = ctx.balance(to) - nativeBefore;
  const receivedUsdc = USDC.balanceOf(to) - usdcBefore;
  require(receivedNative == amountNative, "to received a different native amount");
  require(receivedUsdc == amountNative / scale, "to's USDC balance moved a different amount");

  return { potNative, potUsdc, receivedNative, receivedUsdc };
}