[BUG] Sandbox debug output contaminating JSON stream in Codespaces

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?

Write(CLAUDE_CODE_BUG_REPORT.md)
⎿ Wrote 138 lines to CLAUDE_CODE_BUG_REPORT.md
# Claude Code Bug Report: Sandbox Debug Output Contaminating JSON Stream
## Summary
Claude Code v2.0.47 fails to start in GitHub Codespaces due to sandbox debug messages being written to stdout instead of stderr, causing JSON parsing errors in the
VSCode extension.
## Environment

• Claude Code Version: 2.0.47
• VS Code Version: 1.x (Codespaces)
• OS: Linux (GitHub Codespaces)
• Architecture: x86_64

… +128 lines (ctrl+o to expand)

● Perfect! I've created a comprehensive bug report at /workspaces/x50app/CLAUDE_CODE_BUG_REPORT.md

How to Submit

Option 1: Copy & Paste (Recommended)

1. Open the bug report file:

cat /workspaces/x50app/CLAUDE_CODE_BUG_REPORT.md

1. Go to: https://github.com/anthropics/claude-code/issues/new
2. Copy entire contents and paste into the issue
3. Title: Sandbox debug output contaminating JSON stream in Codespaces

Option 2: Using GitHub CLI (If Available)

gh issue create \
--repo anthropics/claude-code \
--title "Sandbox debug output contaminating JSON stream in Codespaces" \
--body-file /workspaces/x50app/CLAUDE_CODE_BUG_REPORT.md

What I Included

✅ Clear summary - One-sentence problem description
✅ Environment details - Exact versions and platform
✅ Reproduction steps - How to trigger the bug
✅ Log evidence - Exact error messages and timestamps
✅ Root cause analysis - Technical explanation of the bug
✅ Suggested fixes - 3 concrete solutions for Anthropic
✅ Impact assessment - Severity and scope
✅ Investigation history - What we already tried

What Should Happen?

Claude code chat should open and run in vscode with codespace.

Error Messages/Logs

Steps to Reproduce

See above.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.8.47

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_