[BUG] rename command makes sessions unresumable

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?

When running Claude via CLI, sessions renamed via /rename cannot be resumed with --resume or found in the session list. The renamed session disappears from the resume UI entirely.
Session is not listed. Cannot be resumed by name or by browsing.

What Should Happen?

Session appears in the list with its new name and can be resumed.

Error Messages/Logs

Steps to Reproduce

1. Start a new Claude Code session in a project
2. Do some work (send a few messages)
3. Run /rename my-descriptive-name
4. Exit the session
5. Try to resume it (claude --resume or pick from session list)

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.42 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Root Cause:

/rename does not update sessions-index.json (located at ~/.claude/projects/<project-hash>/sessions-index.json). The CLI's resume functionality reads from this index to discover sessions.

Evidence from inspecting the file:

• Active session ID (e.g., 267aeb43-...) is absent from sessions-index.json after /rename
• The .jsonl conversation file exists on disk but the index has no entry pointing to it
• Sessions that were never renamed appear in the index normally