function parseOpId(opId) {
  const match = /^(\d+)@(.*)$/.exec(opId || "")
  if (!match) {
    throw new RangeError(`Not a valid opId: ${opId}`)
  }
  return { counter: parseInt(match[1], 10), actorId: match[2] }
}
Takes a string in the form that is used to identify operations (a counter concatenated
with an actor ID, separated by an `@` sign) and returns an object `{counter, actorId}`.