[BUG] Context leakage between two Claude Code sessions in same working 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?

I am seeing context leakage between two Claude Code sessions when both are opened in the same working directory (same PWD).

Session A:

• Text-only interaction
• No image uploaded

Session B:

• Upload and discuss an image

Observed behavior:
Session A appears to have the image from Session B in its context, even though the image was never uploaded or referenced in Session A.

What Should Happen?

Each Claude Code session should have strictly isolated context.

Images uploaded in one session should never appear or be accessible in another session, even if both sessions are opened in the same working directory (same PWD).

Error Messages/Logs

Steps to Reproduce

1. Open Claude Code (Session A) in a directory
2. Interact using text only (do not upload or reference any image)
3. Open Claude Code (Session B) in the same directory (same PWD)
4. Upload and discuss an image in Session B
5. Return to Session A
6. Observe Session A appears to have the image in its context

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

latest (will paste exact output from claude --version if requested)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Possibly related to issue #7702 (context shared between Claude Code sessions), but in this case it appears to involve image context leakage.

I can provide exact claude --version output and a screen recording if needed.