[BUG] Grep tool returns no results on Windows

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The built-in Grep tool always returns "No files found" on Windows, regardless of whether a path is specified or not. Searching with rg directly via the Bash tool against the same directory returns correct results.

What Should Happen?

The Grep tool should return matching files consistent with running rg directly.

Error Messages/Logs

No error is shown. The tool silently returns "No files found" with no further output.

Steps to Reproduce

1. Open a project containing Rust (or any) source files on Windows
2. Use the Grep tool to search for any pattern expected to match (e.g. fn in .rs files)
3. Observe "No files found" is returned
4. Run rg "fn " --type rust -l via Bash in the same directory — results are returned correctly

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.50 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Running from VSCode. This was tested on a Rust codebase.