[BUG] yukonSilver marked unsupported on official Linux Cowork build despite KVM and vsock both confirmed working

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?

When launching Cowork on the official Linux build of Claude Desktop, the app's internal platform classifier (yukonSilver) reports status=unsupported on every launch, which prevents the VM bundle from ever downloading. Cowork shows a "Virtualization isn't fully set up" dialog directing the user to add themselves to the kvm group.

This is misleading: the actual KVM and vsock prerequisites are independently confirmed working on this system (see verification steps below), yet the yukonSilver check still blocks initialization. The cowork_vm_node.log shows the same "not supported" classification on every launch with no VM boot attempt ever made, matching the pattern reported extensively for Windows builds in issues #25136, #27316, #27420, #29887, #32004, #37016, #43282, #45140, #47327, #48995, and #57717 — all of which conclude this is an app-side platform-detection bug rather than a real system limitation. This appears to be the same bug surfacing on the newly-released Linux build (Linux support shipped 2026-06-30).

What Should Happen?

Cowork should detect that KVM acceleration and vhost_vsock are both available and correctly permissioned, download the VM bundle, and successfully initialize the Cowork workspace — consistent with how yukonSilver is presumably intended to behave when all real prerequisites are met.

Error Messages/Logs

From ~/.config/Claude/logs/cowork_vm_node.log (repeats on every launch, no VM boot ever attempted):

2026-07-02 15:06:04 [info] [VM] Loading vmClient (TypeScript) module...
2026-07-02 15:06:04 [info] [VM] Module loaded successfully
2026-07-02 15:06:04 [info] [linux-vm] Spawning helper: /usr/lib/claude-desktop/resources/cowork-linux-helper
2026-07-02 15:06:04 [info] [linux-vm-helper] [cowork-linux-helper] 2026/07/02 15:06:04.830228 starting (pid=43960, socket=/run/user/1000/claude-cowork-vm.sock)
[cowork-linux-helper] 2026/07/02 15:06:04.830451 [server] listening on /run/user/1000/claude-cowork-vm.sock
2026-07-02 15:06:04 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...

--- System verification performed to rule out real prerequisite issues ---

$ groups $USER
max : max adm cdrom sudo dip plugdev users kvm lpadmin

$ ls -l /dev/kvm
crw-rw----+ 1 root kvm 10, 232 Jul  1 08:33 /dev/kvm

$ sudo -u $USER test -r /dev/kvm -a -w /dev/kvm && echo "ACCESS OK"
ACCESS OK

$ kvm-ok
INFO: /dev/kvm exists
KVM acceleration can be used

$ lsmod | grep vsock
(initially empty — root cause of the original issue was that vhost_vsock was not loaded)

$ sudo modprobe vhost_vsock
$ ls -l /dev/vhost-vsock
crw-rw---- 1 root kvm 10, 241 Jul  2 14:52 /dev/vhost-vsock

After loading vhost_vsock and confirming both device permissions, the yukonSilver check still returns unsupported on every subsequent app restart. No vm_bundle or .img files were found anywhere under ~/.local/share/claude-desktop or ~/.config/Claude, indicating the VM bundle download is never even attempted.

Steps to Reproduce

1. Install Claude Desktop via the official apt repo (downloads.claude.ai/claude-desktop) on Ubuntu 24.04.4 LTS
2. Ensure user is in the kvm group and /dev/kvm is accessible (verified via kvm-ok)
3. Ensure vhost_vsock kernel module is loaded and /dev/vhost-vsock exists with correct permissions
4. Open Claude Desktop and attempt to start a Cowork task
5. Observe: "Virtualization isn't fully set up" dialog appears, directing user to join the kvm group (already satisfied)
6. Check ~/.config/Claude/logs/cowork_vm_node.log — shows yukonSilver not supported (status=unsupported) on every launch, VM bundle never downloads

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

1.17377.2 desktop app linux

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_