getInterfaceOf = val => {
  if (
    !isObject(val) ||
    val[PASS_STYLE] !== 'remotable' ||
    !checkRemotable(val)
  ) {
    // @ts-expect-error narrowed
    return undefined;
  }
  // @ts-expect-error narrowed
  return getTag(val);
}
Simple semantics, just tell what interface spec a Remotable has,
or undefined if not deemed to be a Remotable.

@type {{
<T extends string>(val: PassStyled<any, T>): T;
(val: any): InterfaceSpec | undefined;
}}