[BUG] Changing model in a different session affects ALL sessions across different projects

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 /model to change models in a chat, it changes the model in every chat running even if it is from a different repo completely.
It is not just a visual issue from the terminal status bar that i have installed. i tested by running /model and it actually shows the model i just switched to in a different chat.

What Should Happen?

model choice should persists in each separate chat and not get switched in all chats.

Error Messages/Logs

Steps to Reproduce

open chat A, set model to opus.
open chat B in a different repo, different terminal instance, set model to sonnet
go back to chat A, run /model to see the model set, model will show as "sonnet"

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

i believe 2.0.41 or 40

Claude Code Version

2.0.42

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_