[BUG] API Error 400: Tool use concurrency issues on all file operations

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?

I'm experiencing persistent "API Error: 400 due to tool use concurrency issues" when Claude Code attempts any file operations (Read, Write, Edit, Glob, Bash). This happens immediately when Claude tries to access files, even simple operations like reading a .tscn file or creating a test.txt file.

What Should Happen?

File operations (Read, Write, Edit, Glob, Bash) should execute successfully without concurrency errors.

Error Messages/Logs

API Error: 400 due to tool use concurrency issues.

This error appears every time Claude attempts to use:
- Read tool
- Write tool  
- Edit tool
- Glob tool
- Bash tool (even simple commands like echo "test" > test.txt)

Normal conversation works fine - only file operations fail.

Steps to Reproduce

1. Start Claude Code in project directory: d:\animation\MagiSao\magi-sao
2. Ask Claude to read any file (e.g., "read scenes/main_menu.tscn")
3. Claude attempts to use the Read tool
4. Error immediately appears: "API Error: 400 due to tool use concurrency issues"
5. Same error occurs with Write, Edit, Glob, and Bash operations
6. Creating new chat sessions doesn't fix the issue

Claude Model

None

Is this a regression?

I don't know

Last Working Version

Unknown

Claude Code Version

2.1.19

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

• This started suddenly during a session and persists across completely new chat sessions
• Appears to be a backend API issue, not related to specific project files
• Error specifically mentions "concurrency issues" which suggests a server-side problem
• Date/Time: January 24, 2026