[BUG] Segmentation fault when running multiple Claude Code instances in parallel

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?

Claude Code crashes with segmentation fault when running multiple instances in parallel (e.g., in git worktrees workflow).

What Should Happen?

Claude Code should run stably in parallel instances without crashes.

Error Messages/Logs

[1]    7182 segmentation fault  claude

Steps to Reproduce

1. Set up multiple git worktrees for parallel development
2. Run Claude Code in 2+ terminals simultaneously (in different worktree directories) that actively create subagents with different models (Opus/Sonnet/Haiku)
3. Work normally in each instance
4. Eventually (~1 in 10-15 sessions), one instance crashes with segfault

The crash occurs:

• With or without --dangerously-skip-permissions flag
• Randomly during session (not tied to specific command)

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.19

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Environment

• Claude Code version: 2.1.19
• Node.js version: v20.13.1
• OS: macOS 13.6.6 (Ventura)
• Architecture: x86_64 (Intel Mac)
• Kernel: Darwin 22.6.0

Workaround

Restart Claude Code and use /resume to continue the session. This works reliably.

Additional Context

Using Claude Code with git worktrees workflow where 2-8 parallel instances may run simultaneously in different terminal tabs. Each instance works in its own worktree directory.

No crash logs found in ~/Library/Logs/DiagnosticReports/.

Possible Cause

Race condition in shared resource access (possibly ~/.claude directory, config files, or socket connections) when multiple instances run concurrently.