[BUG] MCP slash command followed by task silently returns empty response in v2.1.132

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?

When an MCP slash command (/superpowers:using-superpowers) is invoked alone (as a workaround for #6657), and the task is sent as a separate follow-up message, Claude Code processes for ~8 seconds and returns a blank response — a single bullet point with no text.

What Should Happen?

Task executes normally, and CC responds with output.

Error Messages/Logs

Steps to Reproduce

1. Open CC v2.1.132 in a project session
2. Send /superpowers:using-superpowers alone
3. Receive "What would you like me to do?" — command works
4. Send a multi-line task as the follow-up message
5. CC shows "Worked for 8s" and renders a blank bullet point — no output

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.132

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

IntelliJ IDEA terminal

Additional Information

This was working in a prior version. The same prompt that now fails worked before v2.1.132. Issue #6657 (closed as not planned) describes the related slash command + inline prompt problem; this is a separate regression where even the split-message workaround fails.