[BUG] Assertion failed in uv_handle_closing durante claude mcp list su 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?

When running the claude mcp list command on Windows, the application crashes with a libuv assertion failure. The MCP server itself works correctly and responds to requests properly, but the Claude Code client fails with a low-level error in the async handling code.

claude mcp list
Checking MCP server health...

lampadina-winforms: http://localhost:5001/mcp (HTTP) - ✓ Connected
Assertion failed: !(handle->flags & UV_HANDLE_CLOSING), file src\win\async.c, line 76

can try here: https://github.com/Walt7/Mcp-Lampadina, project: MCP-Lampadina-WinForms

What Should Happen?

The claude mcp list command should complete successfully and display the available MCP servers without any crashes or assertion failures. It should list the configured MCP servers and their status.

Error Messages/Logs

[Debug MCP]
[12:13:00] 📝 Log pulito dall'utente
[12:13:04] 🌐 POST /mcp da [::1]:62347
[12:13:04] 📨 Body ricevuto: {"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{"roots":{}},"clientInfo":{"name":"claude-code","version":"1.0.113"}},"jsonrpc":"2.0","id":0}
[12:13:04] 🔍 Metodo estratto: 'initialize', ID: 0
[12:13:04] 📤 Risposta inviata: {"jsonrpc":"2.0","id":0,"result":{"protocolVersion":"2025-06-18","capabilities":{"tools":{}},"serverInfo":{"name":"mcp-lampadina-winforms","version":"1.0.0"}}}
[12:13:04] 🌐 POST /mcp da [::1]:62349
[12:13:04] 📨 Body ricevuto: {"method":"notifications/initialized","jsonrpc":"2.0"}
[12:13:04] 🔔 Notifica ricevuta: 'notifications/initialized'. Rispondo HTTP 204 No Content.

Steps to Reproduce

Set up an MCP server (HTTP on localhost:5001)
Verify the MCP server is running and responding to requests correctly
Run claude mcp list command in terminal
The command crashes immediately with the assertion error
Note: The MCP server continues to work fine and can handle other requests

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

1.0.113 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

test winform with .net 4.7 (visual studio 2022) in https://github.com/Walt7/Mcp-Lampadina

The server is a WinForms .NET 4.7 application using HttpListener with KeepAlive=false and responding with 204 to notifications. The error appears to originate from libuv in Claude Code, likely related to keep-alive handling or connections being closed too early.