Userinfo is everything before the last @ of the authority, which ends at / ? # backslash, quotes,
brackets, angle brackets or ASCII whitespace; a path @ (github.com/@user, pkg@1.2.3, a//b@c) is left
alone, non-ASCII stays inside userinfo. Protocol-relative // opens an authority only at a word start.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>