Feature Request: Implement VS Code Agent Integration (@codex hand-off support)

What feature would you like to see?

The OpenAI Codex VS Code extension should integrate with VS Code's Agent framework to enable @codex session hand-off functionality as documented in official VS Code documentation.

Background

According to the official VS Code documentation on Agents:

"You can hand off a local agent session from chat in VS Code by using the Continue In control, or by typing @cli, @cloud, or @codex in your prompt to pass the task to another agent type."

The documentation also states:

"Third party agents are background agents developed by other providers, such as OpenAI Codex, and that are integrated into the VS Code agent experience."

And lists the command: Codex: New Codex Agent: start a new OpenAI Codex agent session in a chat editor

Current Behavior

When typing @codex in VS Code Copilot Chat:

• The @codex participant is not recognized
• No hand-off to the Codex agent occurs
• The documented workflow does not work

Environment Tested

• VS Code Insiders: 1.108.0-insider
• GitHub Copilot: v1.388.0
• GitHub Copilot Chat: v0.36.2026010502
• OpenAI Codex Extension: Installed (openai.chatgpt)
• OS: Windows 11 Pro Build 26200
• Subscriptions: Both ChatGPT Plus AND GitHub Copilot Pro+ (tried both authentication methods)
• Settings tried: Including "Run Codex in WSL" option

Expected Behavior

According to VS Code documentation, users should be able to:

1. Type @codex in chat to hand off a session to the OpenAI Codex agent
2. Use the "Continue In" control to delegate to Codex
3. Run Codex: New Codex Agent command to start a Codex agent session

Technical Implementation Suggestion

VS Code provides the Chat Participant API and the chatSessionsProvider proposed API for third-party agent integration.

The extension would need to:

1. Register a chat participant with name: "codex" in package.json
2. Implement a ChatRequestHandler to handle hand-off requests
3. Optionally integrate with the chatSessionsProvider API for session management in the Agents view

Why This Matters

• The official VS Code documentation explicitly mentions @codex as a supported hand-off target
• Users following the documentation expect this feature to work
• This would enable seamless workflow integration between GitHub Copilot and OpenAI Codex within VS Code

References

• VS Code Agents Overview: https://code.visualstudio.com/docs/copilot/agents/overview
• VS Code Chat Participant API: https://code.visualstudio.com/api/extension-guides/ai/chat
• Related VS Code issue: https://github.com/microsoft/vscode/issues/285933

Additional information

I understand the VS Code extension is currently closed-source (per issue #5822), but this feature request is for implementing the integration that VS Code's documentation already describes as available.