[BUG] C# MCP Server stdio transport fails to connect - health check timeout issue

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?

C# MCP servers using stdio transport fail to connect with Claude Code, even though they work correctly when tested manually.

What Should Happen?

C# MCP Server stdio transport connects successfully

Error Messages/Logs

Steps to Reproduce

Environment:

• Claude Code on WSL2 Ubuntu
• MCP Server: Microsoft's C# SDK (ModelContextProtocol v0.1.0-preview.10)
• Transport: stdio

Issue:
claude mcp list shows "✗ Failed to connect" and /mcp fails with "Failed to reconnect"

Root Cause:
When the MCP server starts with closed/empty stdin, it hangs waiting for input:
timeout 5 /path/to/MssqlMcp < /dev/null
# Hangs until timeout

Manual test shows server works:
echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{...}}' | /path/to/MssqlMcp
# Returns valid JSON-RPC response immediately

Conclusion:
Claude Code's health check doesn't send an initialize request or doesn't properly establish stdio connection. The C# SDK stdio transport expects stdin to be open with data available.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.17

Platform

Anthropic API

Operating System

Ubuntu

Terminal/Shell

PowerShell

Additional Information

_No response_