Lost Updated Files When Undo All Changes

## Problem
When Agentic Coding turn on and the agent made some changes in some files, and then 'Undo all changes', all affected files were deleted but NO original files. They gone and cannot be recovered. It happen twice for me.

## Steps to reproduce the issue

## Expected behavior
Fix the process and provide a backup for any files changed.

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS: Windows 11 Pro
- Visual Studio Code version: 1.000.0
- AWS Toolkit version:
- Amazon Q version: before this version 1.66.0

Start by reproducing the Agentic Coding workflow in Visual Studio Code on Windows 11: make an agent change, then select “Undo all changes.” Trace the undo-all-changes entry point and verify whether the original files remain available. Done means affected files are not lost and a recoverable backup is provided.

Written by the indexing model from the issue text.