mcp-server-git argument injection in git_diff and git_checkout functions allows overwriting local files

In mcp-server-git versions prior to 2025.12.18, the git_diff and git_checkout functions passed user-controlled arguments directly to git CLI commands without sanitization. Flag-like values (e.g., --output=/path/to/file for git_diff) would be interpreted as command-line options rather than git refs, enabling arbitrary file overwrites. The fix adds validation that rejects arguments starting with - and verifies the argument resolves to a valid git ref via rev_parse before execution. Users are advised to update to 2025.12.18 resolve this issue.

Thank you to https://hackerone.com/yardenporat for reporting.