[BUG] Sessions disappear from sidebar — sessions-index.json out of sync with .jsonl files

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?

All previous sessions disappeared from the Claude Code sidebar. Only the current active session is visible. Investigation shows sessions-index.json only lists 2 of 10 .jsonl session files that exist on disk.

What Should Happen?

All sessions with .jsonl files on disk should appear in the sidebar. The sessions-index.json should stay in sync with the actual session files.

Error Messages/Logs

No error messages. The issue is silent — sessions simply don't appear in the sidebar.

Steps to Reproduce

1. Use Claude Code across multiple sessions over several days (10 sessions in my case, spanning Feb 2-9)
2. Notice that previous sessions disappear from the left sidebar
3. Check ~/.claude/projects/<project>/ — all .jsonl session files are still on disk
4. Check sessions-index.json in the same directory — only 2 of 10 sessions are listed
5. The sidebar only shows sessions present in the index file

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.34

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

No data loss — all 10 .jsonl files are intact on disk. The issue is purely that sessions-index.json becomes stale/incomplete, causing the UI to hide sessions that exist.