[BUG] API Error: 400 The request body is not valid JSON: unexpected character: line 1 column 1 (char 0)

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?

Claude Code sessions break after compaction if it had URL in context.

What Should Happen?

It should continue to work :)

Error Messages/Logs

API Error: 400 The request body is not valid JSON: unexpected character: line 1 column 1 (char 0)

Steps to Reproduce

1. Start new session in Claude Code
2. Pass any message with URL, for example can you read this document https://www.anthropic.com/news ?
3. Execute /compact command, wait until completed
4. Ask any follow up question -> observe session is broken due to API Error: 400 The request body is not valid JSON: unexpected character: line 1 column 1 (char 0) error

<img width="1581" height="1071" alt="Image" src="https://github.com/user-attachments/assets/0f1e4126-3cf3-44a8-9173-0eb3067f5755" />

Claude Model

Other

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.207 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_