[BUG] Cloudflare Turnstile 403 loop on macOS — affects both Desktop app and Chrome, Safari works on identical IP

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?

On macOS, both the Claude Desktop app and Chrome 152 are stuck in an
endless Cloudflare Turnstile challenge on claude.ai, returning HTTP 403
on every navigation. Safari 26.6 on the SAME machine, SAME account and
SAME public IP loads and authenticates normally.

This differs from #68674 (labeled platform:windows), where all system
browsers succeeded. Here the failure follows the Chromium engine:
Chrome and the Electron webview both fail, WebKit succeeds.

Notably, https://www.cloudflare.com/cdn-cgi/trace loads fine in Chrome
with no challenge, so this is not a blanket IP block — it is specific
to the Turnstile flow on claude.ai.

Cloudflare Ray ID: a35cf7ed9ecba07d
cdn-cgi/trace (identical in Chrome, Safari and curl):
ip=43.163.72.137 colo=SIN warp=off loc=SG
Egress: Tencent Cloud Singapore

claude_main_tail.txt

What Should Happen?

The Cloudflare Turnstile challenge should complete and claude.ai should
load and authenticate in the Desktop app and in Chrome, as it does in
Safari on the same machine, account and public IP.

Error Messages/Logs

Navigation to https://claude.ai/ failed with status code 403:
Main view load failure #4 (http_error); origin keeps failing, no automatic retry
Turnstile iframe detected. Removing error overlay.
Failed to execute 'postMessage' on 'DOMWindow': The target origin provided
('https://challenges.cloudflare.com') does not match the recipient window's
origin ('https://claude.ai').

OAuth is unaffected — token cache loads and validates normally against
api.anthropic.com. Only the claude.ai webview navigation fails.

Steps to Reproduce

1. Route egress through Tencent Cloud Singapore (43.163.72.137).
2. Launch the Claude Desktop app on macOS, or open https://claude.ai in

Chrome 152.

1. The Cloudflare Turnstile challenge appears and never completes; every

navigation returns HTTP 403 and the view reloads indefinitely.

1. Open the same URL in Safari 26.6 on the same machine — it loads and

authenticates normally.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

defaults read /Applications/Claude.app/Contents/Info.plist CFBundleShortVersionString

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Local causes ruled out:

• No system proxy (scutil --proxy: all disabled)
• IPv6 disabled; curl -6 confirms no v6 path in use
• Third-party cookies set to ALLOW globally, plus explicit exceptions

for [.]cloudflare.com and [.]claude.ai

• JavaScript allowed, no per-site blocks
• Clean Chrome profile (--user-data-dir), all extensions disabled
• Incognito window
• Page translation disabled for the challenge page
• Chrome Secure DNS disabled
• Full reset of ~/Library/Application Support/Claude

Related: #68674 (same signature, Windows, system browsers unaffected)
Platform: Claude Desktop app + claude.ai web (Max subscription), not an API integration.