> I realise this sounds obvious to many people but it clearly wasn't to those guys so maybe it's not!

It's worse: Gemini (and ChatGPT, but to a lesser extent) have started suggesting random follow-up topics when they conclude that a chat in a session has exhausted a topic. Well, when I say random, I mean that they seem to be pulling it from the 'memory' of our other chats.

For a naive user without preconceived notions of how to use these tools, this guidance from the tools themselves would serve as a pretty big hint that they should intermingle their sessions.