git checkout with uncommitted changes causes silent data loss

Problem

Claude Code performs git checkout <branch> on its own initiative (e.g., to switch to a feature branch for committing) while there are uncommitted changes in the working directory. Modified files are silently overwritten by the target branch's version, causing loss of work.

Steps to reproduce

1. User makes changes to files on branch A (doesn't commit yet)
2. Claude Code decides on its own to switch to branch B (e.g., for organizing commits)
3. Claude runs git checkout B — files from branch B overwrite local changes
4. Changes from step 1 are lost without warning

Expected behavior

Claude Code should NEVER run git checkout when there are uncommitted changes. It should either:

• Commit changes first (even as a WIP commit)
• Refuse to switch branches and warn the user about uncommitted changes
• Use git worktree for parallel work

The user did not ask to switch branches — Claude Code made this decision autonomously and destroyed work in the process.

Impact

Lost ~30 minutes of work (CSS changes, template edits across 8 files) that had to be manually recreated.

Environment

• Claude Code CLI
• macOS
• git 2.x