Agents app: In progress updates in session list generating screen cheese

Specifically for cloud sessions providing longer updates, it looks like it's putting the full update in the subheader. I've seen this inconsistently but on two occasions today. Problem resolves itself when there's another update or the session is no longer in progress.

<img src="https://github.com/user-attachments/assets/d1c73a75-6285-43df-9927-4757ae475f5a" alt="Image" width="372" height="81">

