Cowork tasks complete in VM but never render — local_ session ID rejected by UUID validation

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: Cowork tasks complete in VM but never render — local_ session ID rejected by UUID validation

SUMMARY:
Cowork stopped working around 23:30 CET on February 18, 2026. No app update, no system changes. The VM boots fine, tasks run successfully inside it, but the final response never appears in the UI. Chat mode works perfectly. Issue is 100% reproducible and persists after a full nuclear cache reset (deleted Cache, Code Cache, GPUCache, Session Storage, vm_bundles, and Workspaces).

ENVIRONMENT:

• Claude Desktop 1.1.3541 (1e65e4)
• macOS, Apple M3, 24 GB RAM
• SDK version: 2.1.45
• VM bundle version: 0ae58222a1f34cf74c74ce47cc717a82a4eb0f25
• Location: Europe (CET/UTC+1)

WHAT HAPPENS:

1. Cowork starts normally, VM boots and connects
2. Task process spawns successfully inside VM
3. Within seconds, the process gets killed (SIGTERM)
4. UI goes blank — no output ever appears
5. This happens on EVERY attempt

KEY ERROR FROM LOGS (claude.ai-web.log):
[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

CAUSE:
Session IDs are generated in the format "local_xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" but the API endpoint expects a pure UUID. The "l" from "local_" fails validation. The VM completes its work but the renderer crashes when trying to commit the response.

Also present in logs:

• Uncaught Error: Minified React error #418 (hydration mismatch)
• [LOCAL_SESSION] unknown sdk message type: rate_limit_event (floods of these)

WHY THIS IS SERVER-SIDE:

• Same app version (1.1.3541) was working perfectly until ~23:30 CET Feb 18
• No local changes of any kind were made
• Full cache + VM bundle reset did not fix it (fresh VM bundle downloaded, same error)
• Breakage timing aligns with Anthropic infrastructure incidents on Feb 17-18

RELATED ISSUES:

• #18644 — local_ prefixed session IDs rejected by UUID validation
• #18974 — Cowork hangs on "Sending request..." same UUID error
• #20016 — Same bug independently reported
• #25177 — LocalAgentModeSessions.start validation failure
• #26302 — React #418 + EventEmitter leak

WHAT I NEED:
A server-side fix so that local_ prefixed session IDs are either accepted by the API or properly mapped to valid UUIDs before being sent to the validation endpoint.

What Should Happen?

A server-side fix so that local_ prefixed session IDs are either accepted by the API or properly mapped to valid UUIDs before being sent to the validation endpoint.

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce:

1. Open Claude Desktop (version 1.1.3541 on macOS, Apple M3, 24GB RAM)
2. Go to the Cowork tab
3. Select any folder (or no folder — both fail)
4. Create a new task with any prompt (e.g. "Hello" or "List files in this directory")
5. Observe: The task starts, you can see the spinner and initial thinking activity
6. Wait for the task to finish generating its response
7. Observe: The UI freezes — spinner stops, output area goes blank, final response never renders
8. Check ~/Library/Logs/Claude/claude.ai-web.log — you will see:

[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

[LOCAL_SESSION] unknown sdk message type: rate_limit_event (repeated dozens of times)

Uncaught Error: Minified React error #418

1. Check ~/Library/Logs/Claude/cowork_vm_node.log — you will see that the VM process spawned successfully and exited with code 0 (clean exit), but was killed with SIGTERM after only a few seconds
2. Try again — same result every time, 100% reproducible

Additional context:

• Chat mode works perfectly on the same app, same session
• This was working on this exact app version (1.1.3541) until approximately 23:30 CET on February 18, 2026
• No app update, no macOS update, no config changes were made
• A full nuclear reset was performed (deleted Cache, Code Cache, GPUCache, Session Storage, vm_bundles, and Workspaces) — the VM bundle re-downloaded fresh (~12 GB), and the exact same error occurs on the fresh install
• The breakage timing coincides with multiple Anthropic infrastructure incidents logged on status.claude.com on February 17-18, 2026

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.47

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_