[BUG] chat history is shared between multiple sessions in the same directory

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 I have two Claude Code sessions running in the same directory, when I write "Hello A" on session A, then "Hello B" in session B, pressing "up arrow" to get the last message in both sessions shows me "Hello B".

What Should Happen?

Session A should show only the history of session A, and session B should only show session B's history.

Error Messages/Logs

Steps to Reproduce

1. Run two concurrent sessions in the same dir.
2. Write "A" in session A, "B" in session "B" and press enter in both.
3. Press Up Arrow in both sessions, both will show the most recent message in both sessions instead of the most-recent in that particular session.

Claude Model

Not sure / Multiple models

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

Other

Additional Information

Using Kitty with tmux.