[BUG] Dispatch generates unbounded empty turns responding to injected system messages

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?

STOP breaks it, lowercase stop does not

What Should Happen?

Should stop on word stop in any form.

Error Messages/Logs

Claude Code (native CLI): 2.1.226
Claude Desktop:           1.26832.0.0
Bundled CLI:              2.1.222
OS:                       Windows 11 Home 10.0.26200
Model:                    Opus 5

Steps to Reproduce

a wt-cleanup session removed its own worktree registration; the directory remained but git worktree list no longer showed it; the session then spun

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.226

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

<img width="593" height="417" alt="Image" src="https://github.com/user-attachments/assets/b4c26e2e-1e56-48d5-a92f-7715401b6f1d" />

<img width="632" height="904" alt="Image" src="https://github.com/user-attachments/assets/3522236a-4e26-47ef-95f2-5e99ff4fdb95" />