This was maddening: I had written a very long and detailed prompt, then went to select "Codex" from the drop down menu at the top "start a new conversation", and it wiped out the entire prompt I was working on.
Well, of course it did: that drop down is part of the "Start a new Conversation" icon button, but it's position is too far away from the actual icon to infer that is its purpose. It should be a popup that shows the current choice for model (GPT-5, GPT 4.1, Codex).
ANOTHER lost prompt problem. If you have a prompt-in-progress (AI is maybe building some code), and Xcode crashes, it might not save that prompt for when you re-launch.
And how might that happen? Well, there's still numerous ways using the coding assistanty might crash. One I've notice is if you switch out to another app, or if you invoke a screen capture, it might crash.