[BUG] API Error: 400 due to tool use concurrency issues.

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?

After prompt submission I see this "API Error: 400 due to tool use concurrency issues."

What Should Happen?

answer prompt

Error Messages/Logs

API Error: 400 due to tool use concurrency issues.

Steps to Reproduce

create a prompt and press send

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.19

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_