Review `remaining` endpoint response in ElemRoute

The endpoint returns a default RemainingElems when there are no remaining elems.

Start by locating the ElemRoute implementation and tracing the `remaining` endpoint response when no elements remain. Compare that behavior with the endpoint's intended response and existing API conventions; done means the default `RemainingElems` behavior is reviewed and the response matches the established expectation.

Written by the indexing model from the issue text.