I have created a custom AI agent and my goal is to allow users to:

1. Install it via npm OR as a VS Code extension

2. See my agent appear inside GitHub Copilot Chat

3. Select my agent from the dropdown (arrow menu next to the chat input)

I would like to know whether it is technically possible for a third-party npm package or VS Code extension to register itself as a Copilot Chat agent so that it appears in that dropdown.

Is there any official API, Chat Participant API, or Model Context Protocol (MCP) integration method to achieve this?
Or is the Copilot Chat agent dropdown limited to Microsoft-approved agents only?

Additionally, I tried publishing my extension to the Visual Studio Marketplace.

When attempting to create a publisher, it requested a Personal Access Token.
I tried generating one via https://dev.azure.com, but after completing the CAPTCHA and clicking continue, the page does not proceed and remains on the same screen.

Could you please advise:

• The correct process for creating a Marketplace publisher and generating the required access token

• Whether there are known issues with Azure DevOps CAPTCHA verification

• If there is an alternative method to obtain the required access credentials

Thank you for your assistance.