[BUG] Garbled UTF-8 characters in TUI when piping external service output 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?

Description:

OS: Windows 11
Terminal: VS Code integrated terminal + PowerShell 7.5.5
Claude Code version: v2.1.128

Issue: Garbage characters (‘, “, â€") appear in Claude Code's TUI only when it spawns subprocesses to call external services (AWS CLI, Kibo, SFCC). Direct CLI calls from the same terminal work perfectly fine (e.g. aws sts get-caller-identity returns clean output).
Profile settings: chcp 65001, UTF8 encoding set for Console Input/Output, PYTHONUTF8=1, PYTHONIOENCODING=utf-8, AWS_CLI_FILE_ENCODING=utf-8. System-level env vars are clean.
Conclusion: Issue is in how Claude Code pipes/renders subprocess output back into its TUI on Windows, not in the terminal or CLI tools themselves.

What Should Happen?

Description:

OS: Windows 11
Terminal: VS Code integrated terminal + PowerShell 7.5.5
Claude Code version: v2.1.128

Issue: Garbage characters (‘, “, â€") appear in Claude Code's TUI only when it spawns subprocesses to call external services (AWS CLI, Kibo, SFCC). Direct CLI calls from the same terminal work perfectly fine (e.g. aws sts get-caller-identity returns clean output).
Profile settings: chcp 65001, UTF8 encoding set for Console Input/Output, PYTHONUTF8=1, PYTHONIOENCODING=utf-8, AWS_CLI_FILE_ENCODING=utf-8. System-level env vars are clean.
Conclusion: Issue is in how Claude Code pipes/renders subprocess output back into its TUI on Windows, not in the terminal or CLI tools themselves.

Error Messages/Logs

Steps to Reproduce

Description:

OS: Windows 11
Terminal: VS Code integrated terminal + PowerShell 7.5.5
Claude Code version: v2.1.128

Issue: Garbage characters (‘, “, â€") appear in Claude Code's TUI only when it spawns subprocesses to call external services (AWS CLI, Kibo, SFCC). Direct CLI calls from the same terminal work perfectly fine (e.g. aws sts get-caller-identity returns clean output).
Profile settings: chcp 65001, UTF8 encoding set for Console Input/Output, PYTHONUTF8=1, PYTHONIOENCODING=utf-8, AWS_CLI_FILE_ENCODING=utf-8. System-level env vars are clean.
Conclusion: Issue is in how Claude Code pipes/renders subprocess output back into its TUI on Windows, not in the terminal or CLI tools themselves.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.131

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_