[BUG] Add --bg as a valid flag to --help to stop Claude Code getting confused all the time

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?

Now that I'm deep into using claude agents I often ask one sessionto spin off a new one that I want to see in my claude agents view. I think the only way to do that is claude --bg. The problem is Claude doesn't know about this flag, it tries to verify it with claude --help and can't find it, so keeps thinking I'm lying and doing something silly like running it as a Sub Agent.

What Should Happen?

Document --bg in --help so Claude doesn't get confused any more.

Error Messages/Logs

Steps to Reproduce

1. claude agents
2. Open a new session to tell you a joke
3. Ask it start a background agent with claude --bg to research better jokes
4. Watch it fail/do something wrong/ask you about the unknown flag you specified

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.169

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

_No response_