`skill:`, `mailto:` and `skill://` also parse to an empty pathname, with an
empty host, so an empty path alone accepted authority-less URIs the guard
exists to reject. Accept the empty path only when a host is present
(Copilot review round 1).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ2eszDCUqTmhtTMaznw3W
Signed-off-by: cliffhall <cliff@futurescale.com>