Remotable = (
  _iface = 'Remotable',
  props = /** @type {L} */ ({}),
  remoteMethods = /** @type {R} */ ({}),
) => {
  const obj = remoteMethods;
  // Assign props to the object.
  for (const [key, value] of Object.entries(props)) {
    assert(!(key in obj));
    // @ts-expect-error Type 'R' is generic and can only be indexed for reading.
    obj[key] = value;
  }
  const ret =
    /** @type {L & R & import('@endo/eventual-send').RemotableBrand<L, R>} */ (
      obj
    );
  return ret;
}
Mock a Remotable maker.

@template {Record<string, any>} L
@template {Record<string, any>} R
@param {string} [_iface]
@param {L} [props]
@param {R} [remoteMethods]