Claude Cowork on Windows: host runtime when the VM is unsupported, and how custom skills are loaded

Claude Cowork on Windows: runtime and custom skills

Observed 9 September 2026.

Runtime is the host, not a VM (on this install)

%LOCALAPPDATA%\Claude\Logs\cowork_vm_node.log logs on every start:

[startVM] VM not supported (win32/x64, msix_required), skipping

CoworkVMService was not installed and no rootfs.vhdx existed. Cowork therefore ran the Claude Code CLI natively on Windows ("local-agent-mode"), with its working directory under %APPDATA%\Claude\local-agent-mode-sessions\<account>\<org>\local_<id>\outputs.

Consequences:

• Host virtual environments, Windows user environment variables and host paths all work from Cowork skills.
• If the desktop app is reinstalled from the Store as MSIX, the Hyper-V VM becomes supported and host paths stop resolving. A skill that depends on host paths benefits from an environment check at its start.

Skills: Code versus Chat/Cowork are separate

• Claude Code sessions read ~/.claude/skills/<name>/skill.md and ~/.claude/CLAUDE.md.
• Chat and Cowork read neither. Their skills come from the account (claude.ai) and are cached at %APPDATA%\Claude\local-agent-mode-sessions\skills-plugin\<org>\<account>\skills\<name>\SKILL.md, with a manifest.json listing skill ids and creatorType (user or anthropic). The cache is synced from the server, so placing a folder there locally is not durable.
• To add a custom skill, use Customize, Skills, plus, Upload a skill (on claude.ai or in the Cowork sidebar) with a zip containing <name>/SKILL.md. The folder name must equal the skill name.
• PowerShell Compress-Archive writes backslash entry names such as browser-use\SKILL.md, and the upload may then report a missing SKILL.md. Build the zip with Python zipfile using forward slashes.

Sharing one skill body with Claude Code

An @path import at the end of ~/.claude/CLAUDE.md (for example @~/.claude/skills/<name>/skill.md) puts the full skill body into every Claude Code session's context. This was verified with claude -p from an unrelated working directory. The Cowork copy was a separate zip with the same body plus an environment-check section, with the Code copy kept as the source of truth.