[BUG] Cowork fails to start — `srt` binary missing from VM image

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?

What's Wrong?

Cowork consistently fails to start any new task with:

CLI output was not valid JSON. This may indicate an error during startup.
Output: sandbox-helper: failed to start command: fork/exec /usr/local/lib/node_modules_global/bin/srt: no such file or directory

The srt (Sandbox Runtime) binary does not exist anywhere — not inside the Cowork VM, not in the Claude Code npm package on the host, and not anywhere on the filesystem.

Environment

• Claude Desktop: 1.1.2685 (f39a62)
• Claude Code (host): 2.1.39
• Claude Code (VM): 2.1.34 (version mismatch — see logs below)
• macOS: Apple Silicon (ARM64)
• Node.js: v24.3.0 (Homebrew)
• npm prefix: /opt/homebrew (default Homebrew path)

Reproduction Steps

1. Open Claude Desktop → Cowork
2. Start any new Cowork task
3. Task immediately fails with the srt error above

Diagnostic Details

srt does not exist on the host:

$ which srt
srt not found

$ find /opt/homebrew/lib/node_modules/@anthropic-ai/claude-code -name "srt*" 2>/dev/null
(no results)

$ find /opt/homebrew/lib/node_modules/@anthropic-ai/claude-code -name "sandbox*" 2>/dev/null
(no results)

$ find /Applications/Claude.app -name "srt" 2>/dev/null
(no results)

$ find ~/.claude -name "srt" 2>/dev/null
(no results)

VM log shows SDK version mismatch (~/Library/Logs/Claude/coworkd.log):

[coworkd] installed SDK binary v2.1.34 to /usr/local/bin/claude

Host has v2.1.39 but VM installs v2.1.34.

VM boots and connects successfully — networking, session disk, and user recovery all work. The failure only occurs when trying to execute a task, when sandbox-helper attempts to invoke srt.

What I've Tried (none resolved)

• Nuked VM state: rm -rf ~/Library/Application Support/Claude/{vm_bundles,sessions,Cache,Code Cache}
• Fully quit and relaunched Claude Desktop
• Archived old Cowork threads, started fresh sessions
• Reinstalled Claude Desktop from claude.ai/download
• Updated Claude Code to latest (2.1.39)
• Confirmed no MCP connectors are configured

Expected Behavior

The srt binary should be included in the Cowork VM image at /usr/local/lib/node_modules_global/bin/srt, or sandbox-helper should reference the correct path where srt is actually installed.

What Should Happen?

Claude CoWork functions properly

Error Messages/Logs

Steps to Reproduce

Reproduction Steps

1. Open Claude Desktop → Cowork
2. Start any new Cowork task
3. Task immediately fails with the srt error above

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.39 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_