[BUG] "Tool names must be unique" error after MCP server reconnection via /mcp

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?

After reconnecting to an MCP server via /mcp → Reconnect, subsequent operations like /compact fail with error:
Error: API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."}}

This error does NOT occur:

• On initial connection
• When MCP server is disconnected
• Before reconnection

## Environment

• Claude Code Version: 2.0.70
• OS: Windows 11
• MCP Server: Custom stdio server with 17 tools (verified no duplicates in server code)

What Should Happen?

Reconnection should clear the previous tool registration before re-registering tools from the MCP server.

Error Messages/Logs

Error: API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."}}

Steps to Reproduce

1. Start Claude Code in a project with MCP server configured
2. MCP server connects successfully (tools available)
3. Run /mcp
4. Select the MCP server → Reconnect
5. Run /compact (or wait for auto-compact)
6. Error occurs: "tools: Tool names must be unique"

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.0.65

Claude Code Version

2.0.70

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_