After 10-20min of trying different searches for mergeMessageFileList and extension-list and thinking they might be dead leftovers and/or that l10ncache is broken and prod and only considering extensions from some wikis....
... turns out the Scap repo isn't actually included :)
https://gerrit.wikimedia.org/g/mediawiki/tools/scap
Suggesting we add it to "Everything", "Deployed", and "Operations". Basically the same as operations-mediawiki-config. It contains code you'd want to know about when thinking about MW deployed code. But also code you'd want to know abut when searching about operational things.