Windows desktop app crashes when Browser pane opens a Cloudflare-challenged site (preview_start)

Environment

• Claude Code 2.1.97, Windows desktop app
• Windows 11 Home 10.0.26200
• Model: claude-fable-5

Summary

Opening the in-app Browser pane via preview_start with a URL on a site protected by a Cloudflare bot challenge crashes the entire desktop app. Reproduced 6 times in one session; the user had to reinstall the app each time to recover.

Repro

1. In a session, call the Browser pane tool preview_start with {url: "https://crtc.gc.ca/eng/whatsnew.htm"} (this site returns HTTP 403 with Cf-Mitigated: challenge to non-browser clients, i.e. the pane will land on a Cloudflare challenge interstitial).
2. The tool returns successfully (navOk: true, tabId assigned).
3. The desktop app crashes immediately after, before any follow-up tool call completes.

Observed

• Crash occurred on every attempt (6/6). After resuming the session, an immediate get_page_text returned a "No preview is open" error (pane state lost); re-opening with preview_start returned navOk: true again and the app crashed again the same way.
• Plain curl to the same URL confirms the Cloudflare challenge response (403, Cf-Mitigated: challenge, Turnstile CSP headers), so the pane is presumably rendering the challenge page when it dies.

Expected

Worst case the tab should show the challenge page or fail the navigation; the host app should never crash.

🤖 Generated with Claude Code