[BUG] Claude Code on windows desktop fails to recover from API Error 400

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?

You ran into this issue and could not recover.
error API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.3.content.109: thinking or redacted_thinking blocks in the latest assistant message cannot be modified. These blocks must remain as they were in the original response."},"request_id":"req_011Caon6ZHXxT3YBHw1JTLvT"}

Ack. That error = harness bug, not code bug.

Cause: API rejected request because thinking/redacted_thinking block in last assistant message got modified between turns. Anthropic API requires extended-thinking blocks pass back unchanged when tool_use follows.

Common triggers:

Harness re-serializes assistant message, drops/edits thinking block
Mid-stream interrupt then retry without preserving signature
Compaction touched a thinking block it shouldn't
Recovery options:

/clear — fresh conversation, lose context
/compact — compress, may strip thinking blocks cleanly
Restart Claude Code session
Prevention: Not in your control — API/harness contract. If reproducing, file at https://github.com/anthropics/claude-code/issues with request_id: req_011Caon6ZHXxT3YBHw1JTLvT.

What Should Happen?

Respond to prompts.

Error Messages/Logs

Steps to Reproduce

Feedback sent. If you''re working with Anthropic support, include the reference ID below.

a960ac06-7ec2-4d08-88c2-903fba760df6

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.132 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_