[Bug] Linux sandbox (bash) permanently fails — cloud workspace not provisioning for Windows Cowork sessions (6+ sessions affected)

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?

The isolated Linux sandbox fails to start in every Cowork session on Windows. Every bash call returns immediately: "Workspace unavailable. The isolated Linux environment failed to start." This has persisted across 6+ consecutive sessions over multiple weeks with no recovery.

What Should Happen?

The Linux sandbox should start successfully when a Cowork session begins, allowing Claude to execute bash commands, run Python scripts, and perform shell operations. Sessions should have cwd set to /sessions/<name>/mnt/ as was the case before the April 2026 app update.

Error Messages/Logs

Workspace unavailable. The isolated Linux environment failed to start. You can still use file tools directly.

Steps to Reproduce

1. Open Claude Cowork desktop app on Windows (Microsoft Store version)
2. Start any new conversation session
3. Ask Claude to perform any task requiring bash/shell/Python execution
4. Observe Claude calls mcp__workspace__bash
5. Result: immediate failure — "Workspace unavailable. The isolated Linux environment failed to start."
6. Failure is instant with no retry, no startup delay, sandbox never becomes available

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Version before Claude_1.5354.0.0_x64 (last working sessions before 29 April 2026)

Claude Code Version

Claude Cowork 1.5354.0.0 (Microsoft Store, not Claude Code CLI)

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

IMPORTANT: This bug is in Claude Cowork (desktop app), not Claude Code CLI.

KEY FINDINGS:

1. Session cwd format changed after app update:

• BEFORE (working): /sessions/<name>/mnt/
• AFTER (broken): C:\Users\NKB.PRBNS.2111.0025\AppData\Roaming\Claude\local-agent-mode-sessions\...

1. No local sandbox exists — installation inspection confirms:

Path: C:\Program Files\WindowsApps\Claude_1.5354.0.0_x64__pzs8sxrjxfjjc
Contents: app/ and assets/ folders only
NO WSL, Docker, container runtime, or sandbox binary found
%AppData%\Claude does not exist on this machine
Windows Event Viewer shows ZERO Claude entries

Conclusion: Linux workspace is a REMOTE/CLOUD service.
The failure is server-side — nothing to fix locally.

1. Affected sessions (6 confirmed):

local_7922f495, local_b8a680cb, local_83d21f4b,
local_b2a16a18, local_b98a6bbc, local_b5a3f165

1. Working sessions (before update):

local_749d8921, local_b55ec58e, local_9f5155d2, local_95848dc1

1. Anthropic Support Conversation ID: 215474175581735

1. App update date: 29 April 2026 — correlates exactly with regression start