[BUG] API Error: 400 - tool_use ids must be unique when making sequential tool calls

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?

What's Wrong?
When making sequential (non-parallel) tool calls during a conversation, the API returns:

The extension appears to be generating duplicate tool_use IDs, causing the API to reject requests.

This occurs after extended conversations with multiple tool calls. The error is also sometimes displayed as "API Error: 400 due to tool use concurrency issues".

Environment:

• VS Code Extension (Claude Code)
• Windows 11
• Model: Opus 4.5
• Claude Code version: Latest (just updated via npm update -g @anthropic-ai/claude-code)

Steps to Reproduce:

1. Start a conversation in VS Code extension
2. Make multiple tool calls throughout the conversation (file reads, bash commands, etc.)
3. After a single prompt that involves running multiple tool uses the error shows itself.

Workaround:
Running /clear is SUPPOSE to start a fresh conversation temporarily resolves the issue until it reoccurs,
BUT EVEN THIS WORKAROUND DOESN'T WORK!

What Should Happen?

Each tool call should generate a unique ID automatically. Sequential tool calls should execute without ID conflicts regardless of conversation length.

The /clear command should fully reset the conversation state, but currently it does not resolve the issue - the error persists even after clearing.

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.15.content.1: tool_use ids must be unique"},"request_id":"req_011CXSeQMVwcE7aXrAmrs6bY"}

and 

error: 400 due to tool use concurrency issues.

Steps to Reproduce

1. Start a conversation in VS Code Claude Code extension
2. Make multiple tool calls throughout the conversation (file reads, bash commands, glob searches, etc.)
3. After approximately 1-2 tool calls, request another tool call
4. Error occurs: "tool_use ids must be unique" or "API Error: 400 due to tool use concurrency issues"
5. Run /clear to attempt reset
6. Make another tool call
7. Error persists even after clearing

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

~2.1.17 or earlier (approximately 2 versions before 2.1.19)

Claude Code Version

2.1.19 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

• Issue occurs immediately when Claude attempts 2 or more sequential tool calls in a single response
• Does not require extended conversation - can happen on first or second message
• Issue occurs with both Sonnet and Opus models
• Windows 11, VS Code latest version
• Just updated Claude Code via npm update -g @anthropic-ai/claude-code - issue persists
• Completely uninstalled and reinstalled Claude Code, including deletion of ALL cache folders/files - issue persists