Copilot CLI loses todos and edits the wrong plan after forked

[xj-ms]

Describe the bug

If Copilot is asked to update the plan and the todo list, it will update the old plan in the forked session and reports the todo list being empty.

This is likely a problem not only for the plan mode, but whenever it needs to edit a file in the session folder.

Affected version

1.0.78

Steps to reproduce the behavior

1. Ask the agent to create a plan with todos
2. Fork the session
3. Ask it to update the plan and todos

Expected behavior

The agent should edit the plan file and the todo list under the new session folder. The todo list should be copied over for the new session

Additional context

No response