[BUG] Plugin marketplace MCP connector remains stuck "still connecting" when mcp-remote requires OAuth

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?

A Claude plugin installed from an organization plugin marketplace registers an MCP connector correctly, but the connector never becomes available when the connector command uses mcp-remote against a remote OAuth-protected MCP server.

The same mcp-remote command works from a terminal, including browser-based OAuth authorization and successful proxy establishment. In Claude, tool discovery reports that the MCP server is still connecting indefinitely.

Environment

• Claude app / organization plugin marketplace
• Plugin installed from a GitHub-backed Claude plugin marketplace
• MCP in private GitHub repo
• Connector command:

{
  "command": "npx",
  "args": [
    "-y",
    "mcp-remote",
    "https://my-mcp-311582256818.us-east1.run.app/mcp"
  ]
}

Running npx -y mcp-remote https://my-mcp-3115822568178.us-east1.run.app/mcp works correctly: the oauth workflow runs in the user's browser and authentications without issues.

What Should Happen?

Connectors (MCPs) in custom plugins should work in Claude Cowork. Currently, they do not.

Error Messages/Logs

Steps to Reproduce

See above

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude 1.9255.2

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_