Claude Desktop: Black UI after cache clear due to CSP blocking fonts from assets-proxy.anthropic.com

Summary

After clearing the Claude desktop app's cache/files, the UI renders almost entirely black with only a small input box visible. The app becomes unusable until... well, it doesn't self-recover.

Environment

• App version: 1.1.3363
• Commit hash: ee424797ca4d37a06f6b4a1e48dc944838ac3b18
• Platform: macOS darwin arm64 (Apple M2 Ultra)
• OS: 25.3.0

Root Cause (from logs)

~/Library/Logs/Claude/claude.ai-web.log shows the app repeatedly failing to load fonts:

Loading the font 'https://assets-proxy.anthropic.com/claude-ai/v1/_next/static/media/01d1396bd69a228a-s.p.woff2'
violates the following Content Security Policy directive:
"font-src 'self' assets.claude.ai https://js.intercomcdn.com https://fonts.intercomcdn.com".
The action has been blocked.

The CSP font-src directive only allows assets.claude.ai, but the app is now trying to load fonts from assets-proxy.anthropic.com. Every font is blocked, which causes the all-black UI (no fonts = no text rendering).

Steps to Reproduce

1. Clear Claude desktop app cache files (e.g. ~/Library/Application Support/Claude/ cache)
2. Relaunch the app
3. UI loads as a mostly black screen — fonts are blocked by CSP on re-fetch

Expected Behavior

The app should render normally after cache is cleared.

Analysis

This appears to be a CSP mismatch — either:

• A recent update changed the CDN domain from assets.claude.ai to assets-proxy.anthropic.com without updating the CSP to match
• Or the cached assets from the old domain worked fine, but fresh fetches go to the new domain which is blocked

The fix would be to add assets-proxy.anthropic.com to the font-src (and likely script-src, style-src) CSP directives.