[BUG] Cowork: Intermittent "Segmentation fault" on task startup (macOS)

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 starting a Cowork task in Claude Desktop (macOS), the task intermittently fails to load with:

"This task didn't load properly" CLI output was not valid JSON. This may indicate an error during start up. Output: Segmentation fault

Behavior:

• Sending "selam" (a simple greeting) → works fine
• Sending a longer prompt (3-4 sentences) → sometimes works, sometimes segfaults
• The same prompt may work on retry, or fail again — it's non-deterministic
• Once a task fails, subsequent messages in the same Cowork session sometimes get no response at all

Environment:

• Claude Code CLI: 2.1.42
• macOS: Darwin 24.6.0 (Sequoia)
• Claude Desktop: latest version (auto-updated)
• Workspace: folder with CLAUDE.md + markdown docs (no plugins, no .claude-plugin directory)

Steps to reproduce:

1. Open Claude Desktop
2. Create/open a Cowork task pointing to a workspace folder containing a CLAUDE.md
3. Send any message
4. Task fails with "Segmentation fault" error ~50% of the time

Expected: Task should load and respond consistently.
Actual: Intermittent segfault crash on startup, making Cowork unusable.

What Should Happen?

Cowork task should load and respond to messages consistently, without crashing.

Error Messages/Logs

This task didn't load properly
CLI output was not valid JSON. This may indicate an error during start up. Output: Segmentation fault

Steps to Reproduce

1. Open Claude Desktop (macOS)
2. Create a Cowork task pointing to a workspace folder containing a CLAUDE.md file and markdown documents
3. Send any message (even a simple greeting like "hello")
4. ~50% of the time, the task fails with "Segmentation fault" instead of responding
5. Sometimes subsequent messages in the same session get no response at all

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

2.1.42

Claude Code Version

2.1.42

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

This is about the Cowork feature in Claude Desktop macOS app (not Claude Code CLI directly).

• The issue is intermittent/non-deterministic — the same workspace and message may work on retry
• Simple messages like "selam" tend to work more often
• Workspace contains only CLAUDE.md + markdown docs (no .claude-plugin, no custom plugins)
• macOS Darwin 24.6.0 (Sequoia)

<img width="812" height="495" alt="Image" src="https://github.com/user-attachments/assets/9eb49ce5-d09d-422f-8970-0390207169ed" />