Editor scrambled after ctrl+z during edit session

[alexr00]

Testing #274930

My steps, as best as I can tell:

1. Agent mode. Ask for an edit which adds a new method.
2. Edit is made. Accept it.
3. Ask for a second edit, which modified the new method. Accept it.
4. Change my mind about the second edit. Restore check point to after the first edit.
5. Chang my mind about changing my mind, and ctrl + z to bring back the second edit.

[alexr00]

Confirmed those are the steps, as it repro'd a second time.