Sandbox mode leaves read-only bind mounts that persist after disable

Problem

After running Claude Code with the default sandbox mode enabled, certain files get mounted as read-only via bind mounts (likely from the filesystem sandbox implementation). These mounts persist even after disabling sandbox with /sandbox, making it impossible to:

• git checkout -- <file> (error: unable to unlink old file: Read-only file system)
• git stash (same error)
• git pull (same error, can't update the file)
• rm -f <file> (cannot remove: Read-only file system)
• git reset --hard (same)

The only recovery is restarting the entire Claude Code session, which loses all conversation context.

Reproduction

1. Start Claude Code in a git repo with sandbox mode enabled (default)
2. Edit a file that the sandbox has restricted (e.g., .github/workflows/pr.yml)
3. Switch branches or try to pull -- the file is now locked
4. Run /sandbox to disable -- files remain locked
5. All git operations involving that file fail permanently

Environment

• Claude Code CLI on Linux (Fedora/kernel 6.18)
• Terminal: Kitty
• Git repo with GitHub Actions workflows in .github/

Impact

This is a workflow-breaking issue. During a session today, I:

• Could not switch branches
• Could not pull from remote
• Could not push a hotfix to main
• Could not stash or reset
• Had to abandon the session entirely

The sandbox filesystem restrictions should be fully reversible when disabled. Read-only bind mounts must be unmounted on /sandbox disable, not left as zombie mounts that corrupt the working tree.

Expected Behavior

/sandbox disable should:

1. Unmount all sandbox bind mounts immediately
2. Restore full read-write access to all files
3. Allow normal git operations to resume

Alternatively, provide a way to completely opt out of sandbox mode at the project level (e.g., in .claude/settings.json) so it never activates.