[BUG] Cowork 403 "Request not allowed" on Pro plan - Chat works fine

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 tab consistently returns 403 "Request not allowed" every time a task is submitted. Regular Claude Desktop chat works perfectly on the same account.

Error Message
Failed to authenticate. API Error: 403 {"error":{"type":"forbidden","message":"Request not allowed"}}

Environment

• Plan: Claude Pro
• Account email: gipsa4327#proton.me
• Claude Desktop version: latest
• OS: macOS (Apple Silicon)
• Network: api.anthropic.com and claude.ai are both reachable and confirmed accessible

Expected Behavior
Cowork should authenticate and process tasks, same as Chat mode.

Actual Behavior
403 "Request not allowed" every time. Re-login does not help.

What works / What doesn't
| Surface | Status |
|---------|--------|
| Claude Desktop Chat | ✅ Works |
| Claude Desktop Cowork | ❌ 403 Forbidden |
| claude.ai (web) | ✅ Works |

Additional Context

• Previously worked on Windows machine, then started returning "server busy" errors repeatedly, then stopped working entirely
• Fresh install on Mac also fails from the first attempt
• This appears to be a server-side policy rejection (OAuth token exchange succeeds but API rejects the token when used by Cowork)
• Related issues: #32816, #34268

What Should Happen?

Cowork should authenticate and process tasks, same as Chat mode.

Error Messages/Logs

Failed to authenticate. API Error: 403 {"error":{"type":"forbidden","message":"Request not allowed"}}

Steps to Reproduce

1. Log into Claude Desktop with Pro account
2. Open Cowork tab
3. Submit any task (even "Hello")
4. 403 error appears immediately

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude 1.1.8629 (befdfc) 2026-03-24T22:13:01.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

<img width="1126" height="702" alt="Image" src="https://github.com/user-attachments/assets/330a9bf0-c0a9-41af-8243-ed1491328255" />