Codex should probably trigger from a mention in the first issue comment

What version of Codex is running?

github mention

What subscription do you have?

Pro

Which model were you using?

_No response_

What platform is your computer?

_No response_

What issue are you seeing?

In https://github.com/ratatui/ratatui/issues/2178, I mentioned codex when raising an issue. I expected to see this trigger the codex action to look at the issue, but instead saw no action until I added a new comment.

What steps can reproduce the bug?

Create a GitHub issue tagging @.codex

What is the expected behavior?

Codex is triggered to start work

Additional information

_No response_