[BUG] Cannot invoke built-in SubAgents with the @ prefix

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?

I cannot invoke Claude Code's built-in SubAgents with the @ prefix.

What Should Happen?

I should see an option to select the required SubAgent using the @ prefix.

Error Messages/Logs

Steps to Reproduce

Open Claude Code and type '@'. I should be able to see the options to select files, MCP servers and also SubAgents

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.0.25

Claude Code Version

2.0.28

Platform

Google Vertex AI

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_