[Bug] Plan file overwrites existing plan file loses tracking content when creating new plan

Bug Description
[Overwriting existing plan with new plan, losing progress tracking] - ● Done. I've saved the new plan to ui-integration-gaps.md as its own file.

The old happy-chasing-island.md content is unfortunately gone — it wasn't git-tracked and the other chat
overwrote it in place. If you have any notes or recollection of what was in it, I can help reconstruct it.
Otherwise, happy-chasing-island.md currently contains the "4 UI Gaps" plan content which is now duplicated
in the new file.

I'll also save a feedback memory so this doesn't happen again.

To Reproduce:
Work on active plan to near completion. track progress of plan with phases done for later review and verification of what was done.
Now have Claude create a similar plan (these 4 items are still issue, should we work on them?) - Yes and it creates a new plan
The existing plan will be overwritten with the new plan and lost information on the last plan (which may or may not be complete)
The current plan file is stepped on by the new file and lost.

Expected Results
Create a new different plan file for the new effort.

Environment Info

• Platform: win32
• Terminal: windows-terminal
• Version: 2.1.96
• Feedback ID: 54c23267-bd4b-42d1-972e-cf1d35b74019