Clicking markdown links opens URLs with null origin, breaking SPAs

Description

When clicking a markdown link in Claude Code's output, the URL opens in the browser with a null origin instead of a proper HTTP origin. This breaks single-page applications (SPAs) that rely on postMessage or other origin-dependent JavaScript APIs.

Steps to Reproduce

1. Have Claude Code output a markdown link, e.g., [Open Thread in Hex](https://hc.hex.tech/pomelocare/thread/...)
2. Click the link in the terminal output
3. The page opens but is blank/broken

Expected Behavior

The link should open with a proper origin (https://hc.hex.tech), and the page should render correctly.

Actual Behavior

The link opens with origin: 'null', causing JavaScript errors:

Failed to execute 'postMessage' on 'DOMWindow': The target origin provided ('<URL>') does not match the recipient window's origin ('null').

The page remains blank because the SPA's JavaScript fails to initialize properly.

Workaround

Copy and paste the URL into the browser address bar instead of clicking the link. This works correctly.

Environment

• Claude Code version: (current)
• OS: macOS (Darwin 25.2.0)
• Terminal: (default terminal used by Claude Code)
• Browser: (issue observed in browser opened from Claude Code)

Additional Context

This was discovered when using Hex (hex.tech) threads via an MCP integration. The same URL works perfectly when:

• Copy/pasted into the address bar
• Navigated to via in-app links within Hex

The issue is specifically with how Claude Code opens URLs when clicking markdown links.