[BUG] /resume cannot load sessions created with older Claude Code versions

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?

/resume cannot load sessions created with older Claude Code versions

Description

Sessions created with Claude Code v2.1.12 do not appear in the /resume session list when using Claude Code v2.1.37. Only sessions created with the current version are visible.

Root Cause Investigation

After debugging, I found:

• Old session files (v2.1.12) start with {"type":"file-history-snapshot",...} entries
• New session files (v2.1.37) start with {"type":"summary",...} entries
• v2.1.37 appears to only recognize the newer format and silently skips older sessions
• The sessions-index.json file is not read by v2.1.37 — it scans .jsonl files directly
• Deleting sessions-index.json does not trigger a rebuild
• The old .jsonl files are valid JSON and still exist in ~/.claude/projects/

Additional Observations

• Some old session .jsonl files are 20-22 MB despite having only 9-14 messages (index metadata), which may also contribute to them being skipped
• Platform: Windows (MINGW64)
• Project path includes OneDrive directory (unsure if relevant; however, it had been off since before I used Claude code.)

Environment

• Current version: Claude Code v2.1.37
• Old session version: Claude Code v2.1.12
• OS: Windows 10/11 (MINGW64_NT)

Expected Behavior

• /resume should either load sessions from older Claude Code versions or display a message indicating they are incompatible
• Ideally, Claude Code should migrate older session formats automatically

Error Messages/Logs

No Previous Conversation.

Steps to Reproduce

1. Have existing sessions created with Claude Code v2.1.12
2. Update to Claude Code v2.1.37
3. Run /resume
4. Old sessions do not appear in the list (only visible after pressing Ctrl+W, and even then only newer-format sessions show)

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

v2.1.12

Claude Code Version

2.13.37

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other (Git bash)

Additional Information

At first, I was receiving something like "No previous conversation." I started talking with Claude Code itself for debugging, and after a while, I started to see the following, as shown in the image.

<img width="983" height="564" alt="Image" src="https://github.com/user-attachments/assets/6073341e-dea2-4c27-9687-2d5928710150" />