message: don't allow sending 2**64 tokens at once (throw an exception)
diff: @@ -641,6 +641,12 @@ export function makeTokenTransferSkeleton(recipientAddress: string,
  const tokenTypeHexPadded = `00000000000000000000000000000000000000${tokenTypeHex}`.slice(-38)
  const tokenValueHex = tokenAmount.toHex()
  +
  + if (tokenValueHex.length > 16) {
  + // exceeds 2**64; can't fit
  + throw new Error(`Cannot send tokens: cannot fit ${tokenAmount.toString()} into 8 bytes`)
  + }
  +
  const tokenValueHexPadded = `0000000000000000${tokenValueHex}`.slice(-16)
  opReturnBuffer.write('id$', 0, 3, 'ascii')
  