VS Code/Cursor proxy setting prevents Codex extension from exposing/calling Streamable HTTP MCP tools

What version of the IDE extension are you using?

openai.chatgpt 26.5601.20914

What subscription do you have?

ChatGPT Pro

Which IDE are you using?

Cursor

What platform is your computer?

Microsoft Windows NT 10.0.19044.0 x64

What issue are you seeing?

Summary

When a proxy is configured in VS Code/Cursor user settings, the Codex VS Code extension can fail to expose or call configured Streamable HTTP MCP tools. Removing the proxy setting immediately made the same 1C MCP servers callable again.

Environment

• Extension: Codex - OpenAI's coding agent (openai.chatgpt)
• Extension version: 26.5601.20914
• Codex CLI: codex-cli 0.58.0
• Host editor: Cursor / VS Code-compatible extension host
• OS: Windows
• MCP transport: Streamable HTTP
• MCP servers: internal 1C MCP servers, for example:
• http://1c-mcp:8002/mcp
• http://1c-mcp:8003/mcp
• http://1c-mcp:8004/mcp
• http://1c-mcp:8007/mcp
• http://1c-mcp:8008/mcp
• http://1c-mcp:8011/mcp
• http://1c-mcp:8300/mcp

What happened

With a proxy configured in VS Code/Cursor settings, Codex did not expose the configured 1C MCP tools in the active session. Tool discovery did not show the expected MCP tools even though the MCP servers were configured.

At the same time, network-level checks showed that the MCP host and ports were reachable:

1c-mcp resolved to 172.22.111.113
TCP checks succeeded for ports 8002, 8003, 8004, 8007, 8008, 8011, 8300

Direct MCP initialize requests through the same environment returned gateway-level failures before the proxy setting was removed:

HTTP/1.0 502 Bad Gateway

After removing the proxy from VS Code/Cursor settings, the exact same MCP servers became callable from Codex. Verified successful calls included:

• 1c-code-metadata-mcp.stats
• 1c-syntax-checker-mcp.syntaxcheck
• 1c-docs-mcp.docinfo
• 1c-ssl-mcp.ssl_search
• 1c-templates-mcp.list_templates
• 1c-code-checker.onec_help

Expected behavior

Codex should either:

1. Respect VS Code/Cursor proxy settings correctly for MCP connections, including internal host bypass rules, or
2. Provide a clear diagnostic when proxy settings affect MCP tool discovery/calls, for example indicating which MCP URL failed through the proxy and suggesting NO_PROXY / proxy bypass configuration.

Actual behavior

The extension appeared as if the MCP tools were unavailable/not exposed, while the underlying cause was a VS Code/Cursor proxy setting. The failure mode was not obvious from the Codex UI.

Reproduction outline

1. Configure a Streamable HTTP MCP server on an internal hostname, e.g. http://1c-mcp:8002/mcp.
2. Configure a proxy in VS Code/Cursor user settings.
3. Start Codex extension and check available MCP tools.
4. Observe that expected MCP tools are missing or calls fail.
5. Remove the proxy setting from VS Code/Cursor settings.
6. Restart/reload Codex extension session.
7. Observe that the same MCP tools are now callable.

Notes

This may be related to proxy handling for extension-host HTTP requests to MCP servers. The important diagnostic gap is that Codex currently surfaces the symptom as missing/unavailable MCP tools, while the actionable cause is the editor proxy setting.

What steps can reproduce the bug?

What steps can reproduce the bug?

1. Configure a Streamable HTTP MCP server on an internal hostname, for example `http://1c-mcp:8002/mcp`.
2. Configure a proxy in VS Code/Cursor user settings.
3. Start the Codex extension and check available MCP tools.
4. Observe that the expected MCP tools are missing or calls fail.
5. Remove the proxy setting from VS Code/Cursor settings.
6. Restart or reload the Codex extension session.
7. Observe that the same MCP tools are now callable.

### What is the expected behavior?

Codex should either respect VS Code/Cursor proxy settings correctly for MCP connections, including internal host bypass rules, or provide a clear diagnostic when proxy settings affect MCP tool discovery or calls.

### Additional information

_No response_