I wonder if it's the same behavior as copilot cli. I dug into it when I got annoyed and found that there's a fundamental tension between rendering the cell based UI and supporting the terminal's native copy paste. At least on copilot cli there were extra zero width characters being copied.

My memory is that once you begin using the alternate screen, you need to turn on mouse reporting, and then you lose native copy. Different terminal emulators also act totally differently when in this state.