Rest doesn't mean no state in the world exists. It's not a violation at all that an endpoint changes its output. Rest only reasons about idempotency, not reproducibility.
> Rest only reasons about idempotency, not reproducibility.
Absolutely. If you GET a collection resource, then POST a new item into the collection, then GET the collection again, the response will have changed. Having these kind of temporal dependencies on the answer you receive is not something REST argues against.
