[BUG] MCP server "mcp-registry" shows connection error on every session start

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?

Every time a new conversation or session is started in the Claude desktop app (macOS), an error toast appears saying "Could not connect to MCP server
mcp-registry". This also intermittently affects the built-in "Claude in Chrome" server. No user-configured MCP servers are involved —
claude_desktop_config.json has "mcpServers": {}.

The root cause is a connection lifecycle bug: when a new session is initialized, the web renderer calls connect-to-mcp-server for the built-in mcp-registry
internal server without first closing the existing connection from the previous session. The MCP SDK's Protocol instance rejects the second connection.

What Should Happen?

No error toast on session start. The previous transport should be closed before reconnecting, or a separate Protocol instance should be used per session.

Error Messages/Logs

From ~/Library/Logs/Claude/claude.ai-web.log:

  [MCP] Could not connect to MCP server mcp-registry Error: Error invoking remote method
  'connect-to-mcp-server': Error: Already connected to a transport. Call close() before
  connecting to a new transport, or use a separate Protocol instance per connection.

  From ~/Library/Logs/Claude/main.log, showing repeated connection requests without cleanup:

  2026-02-23 20:08:57 [info] MCP Server connection requested for: mcp-registry
  2026-02-23 20:08:58 [info] MCP Server connection requested for: mcp-registry
  2026-02-23 20:11:52 [info] MCP Server connection requested for: mcp-registry
  2026-02-23 20:11:53 [info] MCP Server connection requested for: mcp-registry

Steps to Reproduce

1. Open the Claude desktop app on macOS
2. Start a new conversation
3. Observe the error toast "Could not connect to MCP server mcp-registry"
4. Start another conversation — the error appears again

The error has been occurring across multiple app versions since at least late January 2026.

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.52

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_