Very little, overall.

This system was actually built incrementally over several months and did not start out as a full VCS -- it started as a read-only service that ingested data from our Git repo to take pressure off of CI and other tools needing to materialize checkouts for certain types of repo/graph questions. Even when we did decide to go all the way, we were operating in a hybrid Git/Scion world for months during the migration and the path to get there made the system and code very unique to our infrastructure.