[BUG] Cowork's code execution / Linux sandbox won't start. Every shell command returns "Workspace still starting — the isolated Linux environment is booting in the background,"

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?

Cowork's code execution / Linux sandbox won't start. Every shell command returns "Workspace still starting — the isolated Linux environment is booting in the background," and it never finishes (waited well past 30 seconds, many times). File and web tools work fine; only bash/code execution is dead.
I originally got a popup to reinstall a component (I believe the sandbox VM). Since then I've tried: fully quitting/relaunching, rebooting, reinstalling the latest Claude Desktop, and starting fresh conversations. Still broken.
This is a personal Mac, so no MDM/endpoint security is involved. Specs: MacBook Pro 14" 2021, Apple M1 Max, 32 GB RAM, ~248 GB free, macOS Tahoe 26.5.1, latest Claude Desktop, Claude 1.12603.1 (3df4fd) 2026-06-11T16:57:36.000Z. The Cowork VM simply won't launch despite the machine being well within requirements.

What Should Happen?

The Linux sandbox boots within ~10–30 seconds and the shell command runs (returns output like uname, Python version, etc.).

Error Messages/Logs

Every shell/code command returns the error "Workspace still starting — the isolated Linux environment is booting in the background (usually 10–30 seconds). Try again shortly." The VM never finishes booting, no matter how long you wait or how many times you retry. File reads/writes and web tools still work — only code execution is affected.

Steps to Reproduce

1. Open Claude Desktop on macOS and start a Cowork conversation.
2. Ask Claude to run any shell/code command (e.g. "test the Linux sandbox" or anything that triggers bash/code execution).
3. Observe that the command never executes.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.12603.1 (3df4fd) 2026-06-11T16:57:36.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_