If clients know you have a local relay and a relay has implemented the "only event IDs" query, then the client could just pull all of the IDs from the remote relay, compare to the local one, and each other, and then only pull one copy of the events that are missing, right? Wouldn't that cut down on...

I haven't heard about "Citrine", yet. How does this work?

There's a nostruel for mobile ? or are you using the web version ?