[BUG] 2.0.17 Stop hook systemMessages accumulate

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?

Every time a new systemMessage is sent from Stop hook the previous Stop systemMessages are resent along with the new message. Notification hook does NOT do this(only the new message is displayed each time).

What Should Happen?

It should only show the new message just sent via the hook response json.

Error Messages/Logs

Steps to Reproduce

add systemMessage to json response from Stop hook and sys.exit(0).

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.0.15

Claude Code Version

2.0.17

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Windows Terminal

Additional Information

This is in WSL2 Linux(Debian or Ubuntu which ever is the normal default for WSL2)