[BUG] SessionStart hooks break input after execution on Windows

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 I set up a SessionStart hook, the input field breaks after it runs. The text ^[[I briefly appears underneath the input field after the hook executes, and then all subsequent input continues in that space underneath the input field. Other terminal inputs produce other control codes (^[[O when unfocusing etc.). I do not have any issues with hooks on MacOS, only on Windows.

<img width="812" height="101" alt="Image" src="https://github.com/user-attachments/assets/311b6670-2713-4d70-bf62-f4dc595ab45b" />

After typing \, the input field seems to fix itself.

What Should Happen?

The input field should not break after the hook runs.

Error Messages/Logs

Steps to Reproduce

1. Create a config file at .claude/settings.local.json with the following content:

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "startup",
        "hooks": [
          {
            "type": "command",
            "command": "echo OK"
          }
        ]
      }
    ]
  }
}

1. Run Claude Code (claude)
2. Observe the text ^[[I print briefly underneath the input, and then the input field breaks, as noted above.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.30

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

This happens in both Powershell and Git Bash. This also occurs with SessionStart hooks from plugins (I was only attempting to use hooks to replace my deprecated output styles).