[BUG] Sessions lost since upgrade to 2.1.31 (downgrading to 2.1.29 fixes it)

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 come to use Claude Code tonight and /resume look like this:

<img width="1732" height="575" alt="Image" src="https://github.com/user-attachments/assets/e534eac5-55b8-43b4-819e-bc037784495e" />

That is a LOT less chat sessions than I've seen previously, and you can see some seem to be outputting tags.

Asking Claude about this, he downgraded me to 2.1.29, and the sessions are back:

<img width="1811" height="956" alt="Image" src="https://github.com/user-attachments/assets/30047f46-5168-4c46-b3e2-e077929fdaa9" />

And then when I get auto-upgraded to .31 again, the sessions history broke again. Until Claude and I worked out that deleting the sessions-index.json AND downgrading seemed to keep the conversation history intact.

Is this isolated to me or an issue with .31 generally? Here's what Claude said was happening when I was originally on .31 and past chats were broken:

<img width="1857" height="463" alt="Image" src="https://github.com/user-attachments/assets/89a62eff-119d-47b2-b650-cc4435d9dd38" />

Here's Claude seeing it is a corrupted sessions-index.json file and saying when I relaunch with "claude /resume" the index is rebuilt successfully. But only with 2.1.29.

<img width="1145" height="585" alt="Image" src="https://github.com/user-attachments/assets/76a0c747-6a7c-4760-96c8-57f730539257" />

What Should Happen?

Version 2.1.31 should stop losing my past chats!

Error Messages/Logs

Steps to Reproduce

• I guess if conversation histories don't break on upgrade to 2.1.31, then you can't! But if you do:
• delete sessions-index.json
• quit
• re-run Claude Code with "claude /resume"

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.29

Platform

Other

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

Using tmux over SSH within a Debian environment