Markdown hyperlinks open with 'undefined' prefix in URL (e.g. undefinedgithub.com)

[nekdima]

Bug Description

All clickable hyperlinks rendered by Copilot CLI in terminal output are prefixed with undefined, making them open broken URLs.

Example: A markdown link [repo](https://github.com/user/repo) or bare URL https://github.com/user/repo opens as:

https://undefinedgithub.com/user/repo

Reproduction Steps

1. Start a Copilot CLI session (v1.0.15)
2. Ask Copilot to output any markdown with URLs (bare, [text](url), or in code blocks)
3. Click any hyperlink in the terminal output
4. The browser opens with undefined prepended to the hostname

Expected Behavior

Links should open the correct URL without any prefix.

Actual Behavior

Every hyperlink gets undefined prepended to the hostname:

• https://github.com/... → https://undefinedgithub.com/...
• https://learn.microsoft.com/... → https://undefinedlearn.microsoft.com/...

Root Cause (from binary analysis)

The embedded JavaScript URL resolver uses baseUrl which evaluates to undefined. When constructing terminal hyperlinks (OSC 8), the renderer does string concatenation: "undefined" + "github.com" → "undefinedgithub.com".

Relevant strings found in the binary:

get baseUrl() { return this.baseUrl?.origin; }

When this.baseUrl is undefined, the optional chaining returns undefined, which gets stringified during hyperlink construction.

Suggested fix: Add a nullish coalescing fallback: this.baseUrl?.origin ?? "" or skip base URL prepending for absolute URLs.

Environment

• Copilot CLI: v1.0.15-0
• macOS: Sequoia (arm64)
• Terminal: iTerm2 + default Terminal.app (both affected)
• render_markdown: true in config.json

Workaround

Setting render_markdown: false avoids the bug but disables all rich formatting.

[nekdima]

Closing — root cause was my local Finicky (macOS URL router) config, not Copilot CLI. The rewrite function returned a partial plain object instead of the full URL object, causing undefined to be interpolated into the hostname. Fixed in .finicky.js. Sorry for the noise!