[Bug] Anthropic API Error: 403 Forbidden on Cowork Session Registration

Bug Description
### Environment

• Claude Desktop version: 1.3109.0
• OS: macOS 26.4.1 (Build 25E253)
• Kernel: Darwin 25.4.0 arm64 (Apple Silicon)
• Account plan: [Max
• Region / Network: [US]

### Symptoms

• Chat mode works normally
• Existing Cowork conversations continue to function
• Creating a new Cowork task fails immediately with 403
• Cache clearing, relogin, cookie reset — all ineffective

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

### Relevant log entries (from ~/Library/Logs/Claude/main.log)

First failure — OAuth authorize rejected:
2026-04-16 12:25:41 [info] oauth failed: authorize returned 403 {
"type": "forbidden",
"message": "Request not allowed"
}
2026-04-16 12:25:41 [error] [sessions-bridge] Persistent 403 after retry, giving up: …
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