I can't see the previous discussion, when I get added to a room. I just see what arrives after I got there. I was thinking it might be cached. 🤷‍♀

Not exactly. It uses a coordinator where messages are stored so async comms can happen. The coordinator is a cvm server ( which is basically rpc over nostr contextvm.org ) so relays are just uses as an ephemeral bus for commands/messages. All messages are ephemeral and encrypted so the identity of the sender, receiver or even the cordn being used is totally obfuscated across other cvm traffic. Also coordinators are as dumb as relays and learns nothing (almost, nothing insightful in any case), and ofc you can deploy your own coordinator easily for maximum privacy/sovereignty

Check https://cordn.net