[BUG] /rename loses conversation history before the rename point

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?

## Description

When renaming a session using /rename <new-name>, all conversation history
before the rename becomes inaccessible. Resuming the session — either by the
new name or by session ID — only shows messages from after the rename.

## Impact

History loss on rename makes the feature dangerous to use — users expect
rename to be safe and reversible, but it silently discards conversation context.

What Should Happen?

Renaming a session should be a cosmetic operation. The full conversation
history (before and after rename) should remain accessible when resuming.

Error Messages/Logs

The session appears to start from the rename point. All prior messages are
  not shown in the UI, even though the `.jsonl` file for the session is large
  (~18 MB), suggesting the data may still be on disk but is not rendered.

Steps to Reproduce

1. Start a session and have a long conversation
2. Run /rename new-session-name inside the session
3. Exit and run claude --resume new-session-name (or claude --resume <session-id>)
4. Only history after the rename is visible — everything before is gone

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.63

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

## Environment

• OS: macOS 15 (Darwin 24.6.0)
• Claude Code CLI version: 2.1.63