[BUG] Cowork hangs on "Starting up…" indefinitely + every message crashes — Windows 10 Pro, Desktop 1.8555.2.0

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 is completely unusable on my machine. Existing sessions hang on "Starting up…" indefinitely (8+ minutes with no progress), and every message I attempt to send (even when starting brand new Cowork sessions) crashes the Cowork session immediately.
Regular Claude chat works fine — only Cowork is affected.

What Should Happen?

Expected Behavior
Cowork should start a working session and accept messages without crashing.

Error Messages/Logs

2026-05-23 22:31:56 [info] [VM:start] Beginning startup
2026-05-23 22:31:58 [info] [VM:steps] vm_boot completed (334ms)
2026-05-23 22:32:06 [info] [VM] Network status: CONNECTED
2026-05-23 22:32:09 [info] [VM] API reachability: REACHABLE
2026-05-23 22:32:11 [info] [VM:steps] sdk_install completed (4027ms)
2026-05-23 22:32:11 [info] [VM:start] Startup complete, total time: 14891ms

Steps to Reproduce

Steps to Reproduce

Open Claude Desktop 1.8555.2.0 on Windows 10 Pro
Open Cowork
Start a new session with any model (reproduced on Opus 4.7)
Send any message
Observe: session shows "Starting up…" spinner indefinitely; any sent message crashes the session

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Exact previous version unknown — Claude Desktop auto-updates and the previous build was replaced. Cowork worked reliably for me up until very recently. Earliest log evidence of successful Cowork spawn is on version 1.2278.0.0 (2026-04-13), but Cowork continued working through multiple subsequent updates before breaking.

Claude Code Version

Current broken version is 1.8555.2.0.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

VM boots cleanly, network connects, API is reachable, SDK 2.1.149 installs successfully. The crash appears to happen at the task spawn layer after the VM is healthy — consistent with the pattern in #49367 and #49485, but on Windows 10 Pro rather than macOS.
I'll attach the full cowork_vm_node.log to this issue.

Possibly relevant: Windows 10 Pro rather than Windows 11. The Cowork documentation primarily references Windows 11, but Windows 10 Pro has the required Hyper-V components and the VM service runs without error, so the failure appears to be downstream of platform compatibility. Using Windows PowerShell 5.1.19041.6456

cowork_vm_node.log