[BUG] .mcp.json not loaded when project is in Windows drive root (e.g. B:\)

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?

When a project is opened directly from the root of a Windows drive (e.g. B:\),the .mcp.json file is not discovered and MCP servers are not loaded. No error is shown — the tools are simply unavailable.

What Should Happen?

.mcp.json placed in the project root should be discovered and MCP servers should load, regardless of whether the project root is a drive root (B:\) or a subdirectory (B:\myproject\).

Error Messages/Logs

None. The MCP server silently fails to load with no warning or error message.

Steps to Reproduce

1. Use a Windows drive root as project root (e.g. B:\ mapped via SMB)
2. Place .mcp.json in B:\.mcp.json
3. Open the project in VSCode with Claude Code
4. MCP tools are unavailable

Workaround: moving the project to B:\myproject\ and placing .mcp.json there works correctly.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.91

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

Drive B:\ is a network drive mapped via SMB to a Synology NAS. The issue is specific to drive roots — subdirectory projects work as expected.