[BUG] OAuth authentication failure - hour of lost productivity

Description

OAuth login flow is broken. Browser-based OAuth completes successfully but Claude Code fails to pick up the token, timing out. This has cost approximately one hour of productive work time today (2026-03-11).

Environment

• OS: Windows 11 Pro 10.0.26200
• Claude Code: Latest
• Platform: Windows (bash shell)
• Account: Pro subscription

What happened

1. Attempted to authenticate Claude Code via OAuth
2. Browser opened, Google/Anthropic sign-in completed successfully
3. Claude Code never received the callback -- timed out
4. Multiple retry attempts over ~1 hour, same result each time

Expected behavior

OAuth flow should complete and authenticate the CLI session within seconds of browser approval.

Impact

• Lost productivity: ~1 hour of billable work time
• Severity: Complete blocker -- cannot use the tool without authentication
• Workaround: None available during the outage window

Notes

This appears to be part of a wider outage affecting multiple users today (see #33258, #33213, #33238, #33269, #33228). The root cause appears to be DNS resolution failures on auth.anthropic.com and/or Cloudflare challenge race conditions blocking the OAuth callback.

Paying customers should not be losing hours of productivity to authentication infrastructure failures. Request: post-incident review and improved error messaging so users know it's a service-side issue rather than spending time debugging locally.