needs a field to not return a given set of IDs for a start

a signal for more available in that time range before the end of the window would be useful also, in the result, so you can put a "since" in a subsequent and get pages in a dense patch or wide window or minimal filter (like `{"kinds":[1]}` )

there is some complications with this stuff because of concurrency and timestamp divergence and tolerance, that probably needs some extra thing too, in the EVENT envelope to signify it's new or a rebroadcast