[BUG] Cowork workspace fails with "SDK version 2.1.260 not verified" on Windows 11 Pro 26200.9445 — persists after full claude-code-vm cache deletion and repeated reinstalls

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?

Summary

Every Cowork session on Windows 11 Pro fails to start its Linux workspace. Any shell/bash tool call returns:
Workspace unavailable. The isolated Linux environment failed to start
(RPC error -1: SDK version 2.1.260 not verified at
/mnt/.virtiofs-root/shared/c/Users/<USER>/AppData/Roaming/Claude/claude-code-vm/2.1.260/.verified)

What Should Happen?

The first call in a session instead returns Workspace still starting, then every subsequent call returns the error above. The failure is deterministic — it reproduces on every new session and never self-recovers.

Practical impact: file tools (Read/Write/Edit) still work, but they cannot read binary formats. With no shell, Cowork cannot open .docx or .xlsx files at all, which makes the feature unusable for document work.

Environment

OS Windows 11 Pro, 10.0.26200 (build 26200.9445)
Cowork SDK version 2.1.260
Install type Claude Desktop
Virtualization Enabled (Cowork previously worked on this machine)

Previously working SDK versions on this same machine, per cowork_vm_node.log: 2.1.170 and 2.1.181 (both started normally, June 2026).

Possible trigger — recent Windows updates

Two updates were installed shortly before the failure began:

2026-09 Security Update KB5124008 (brings build to 26200.9445)
2026-09 .NET Framework Security Update KB5126052

Noting the correlation only — I have not isolated causation. Given that these updates touch the servicing stack and .NET, they may be resetting service startup state or affecting the HCS/virtiofs components the VM depends on. Worth checking whether other reporters on 26200.9445 see the same thing.

Error Messages/Logs

Steps to Reproduce

Launch Claude Desktop on Windows 11 Pro 26200.9445.
Start a Cowork session with a connected folder.
Invoke any shell/bash tool call.
First call returns Workspace still starting; all later calls return the SDK version 2.1.260 not verified RPC error.
Expected behavior

The workspace VM starts, or the SDK is re-downloaded and verified so that .verified is written for the installed version.

Actual behavior

The VM never becomes usable. The error points at a missing/unwritten .verified marker for 2.1.260 and there is no automatic re-download, repair, or fallback to a previously verified SDK version.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.49585.0.0

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_