Cross-session message contamination between parallel CLI sessions

Description

When running two Claude Code CLI sessions in parallel (separate terminal tabs/windows on the same machine), content intended for Session A appeared in Session B's initial message. The user typed a message about testing parallel Bible translations in one session tab, but that text appeared in a completely different session where they only asked about fixing two backend bugs.

The user confirmed they did NOT type that text in the affected session — it was meant for a parallel session in another tab.

Steps to Reproduce

1. Open two terminal tabs/windows
2. Start claude in both tabs (two independent parallel sessions)
3. Type a message in Tab A (e.g. about testing parallel translations)
4. Type a different message in Tab B (e.g. about fixing backend bugs)
5. Tab B's context contained text from Tab A's intended message, merged into Tab B's first message

Expected Behavior

Each CLI session should have completely isolated input. Messages typed in one session should never appear in another session's context.

Actual Behavior

Text from one session's input appeared in another parallel session's first message, as if the messages were merged or the input buffer was shared.

Environment

• OS: Windows 11 Pro 10.0.26200
• Shell: Git Bash (via VS Code terminal)
• IDE: VS Code with Claude Code extension
• Model: claude-opus-4-6
• Multiple sessions: Yes, two parallel sessions in separate terminal tabs

Impact

This can lead to:

• Confusion about what was requested in each session
• Wasted tokens/context on unintended tasks
• Potential privacy concerns if sessions contain sensitive data meant for different contexts