[BUG]

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?

Bug Description
Cowork gets stuck on "Preparing session..." and never starts. After a couple of minutes, it shows only the Claude icon with no text output. The VM starts successfully and the process spawns, but gets killed with SIGTERM almost immediately, or no response is ever displayed.
Root Cause
The claude.ai-web.log shows this error repeatedly:
[REACT_QUERY_CLIENT] QueryClient error: Error: path.conversation_uuid: Input should be a valid UUID, invalid character: expected an optional prefix of urn:uuid: followed by [0-9a-fA-F-], found l at 1
It appears the local_ prefix in session paths (e.g., local_8968c21e-171d-489a-bee1-b91f91cea48a) is being incorrectly passed to an API endpoint that expects a proper UUID format.
What I've Tried
All of the following did not resolve the issue:

Restarting Claude Desktop
Clearing ~/Library/Application Support/Claude/local-agent-mode-sessions/
Clearing ~/Library/Application Support/Claude/vm_bundles/
Clearing ~/Library/Caches/Claude/
Clearing ~/Library/Application Support/Claude/Partitions/

The error persists across all cleanup attempts, suggesting the invalid state may be stored server-side or in a location not covered by these directories.

What Should Happen?

Cowork should start and display Claude's response.

Error Messages/Logs

From claude_vm_node.log, the VM starts successfully:
[VM:start] SDK installed, total startup time: 7686ms
From sdk_daemon.log, the process spawns but sometimes gets killed immediately:
[process:1f7cf1cd-...] started PID 1539
[process:1f7cf1cd-...] sending SIGTERM to PID 1539
From claude.ai-web.log, the UUID error appears every time Cowork tries to start:
[REACT_QUERY_CLIENT] QueryClient error: Error: path.conversation_uuid: Input should be a valid UUID, invalid character: expected an optional prefix of `urn:uuid:` followed by [0-9a-fA-F-], found `l` at 1

Steps to Reproduce

no idea

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude 1.1.381 (c2a39e) 2026-01-18T20:18:52.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_