claude-code - 💡(How to fix) Fix [BUG] Image upload in cloud environment poisons session — all subsequent API calls return 400, /compact cannot recover [1 comments, 2 participants]

Uploading an image file to an active Claude Code session produced a malformed assistant turn that cannot be recovered from. Every subsequent message returns HTTP 400 from the messages API. /compact fails with the same error because it replays the poisoned history.

Error Messages/Logs

The image upload created an assistant message containing an empty text block, and the prompt cache breakpoint was attached to that empty block. Subsequent requests fail validation on either the empty text or the cache_control marker on it. Because the bad turn is now in persistent history, every replay including /compact triggers the same validation error.

TL;DR

Remove the empty text block created by the image upload to prevent validation errors and allow the session to recover.

Guidance

• Verify that the issue is caused by the empty text block by checking the request IDs and error messages for patterns related to cache_control and empty text blocks.
• Attempt to manually remove the problematic turn from the conversation history to see if the session recovers.
• Consider adding a check before sending messages to ensure that text blocks are not empty and do not contain cache_control markers.
• Investigate why the image upload is creating an empty text block and attach the image to the next user turn instead.

Example

No code snippet is provided as the issue does not contain sufficient information about the implementation details.

Notes

The root cause of the issue is likely related to the image upload creating an empty text block, but the exact implementation details are unclear. The provided guidance is based on the error messages and the probable root cause speculation.

Recommendation

Apply a workaround to remove or prevent the creation of empty text blocks until a permanent fix is available, as the issue has a medium-high severity and can cause session-destroying errors.