In e.g. https://www.mediawiki.org/wiki/Special:Version , the MediaWiki, skin, and extension versions all have a git commits SHA that links to, e.g., https://git.wikimedia.org/tree/mediawiki%2Fcore.git/36f661cf4799ec1b7fbe481a54e62afbd46133e0 , etc.
$wgGitRepositoryViewers in DefaultSettings.php maps from gerrit.wikimedia.org URLs to git.wikimedia.org/tree URL patterns. I think we could replace git.wikimedia.org with a diffusion pattern (but again, callsigns ☹ ). Eventually if diffusion is the origin git repository, .git/config in production would have origin = lines pointing to diffusion, and the mapping becomes simpler.