getInterfaceMethodKeys = interfaceGuard => {
  const { methodGuards, symbolMethodGuards = emptyCopyMap } =
    getInterfaceGuardPayload(interfaceGuard);
  /** @type {(string | symbol)[]} */
  // TODO at-ts-expect-error works locally but not from @endo/exo
  // @ts-ignore inference is too weak to see this is ok
  return harden([
    ...Reflect.ownKeys(methodGuards),
    ...getCopyMapKeys(symbolMethodGuards),
  ]);
}
@param {InterfaceGuard} interfaceGuard
@returns {(string | symbol)[]}