Go Git and Dulwich and friends are indeed fun tech.

ZeroFS (https://github.com/Barre/zerofs) is 9P/NFS/NBD over S3 on an LSM. Point stock go-git, or just /usr/bin/git, at a mount and skip the gymnastics. Rename is a metadata op in the keyspace, so you get it atomic on any S3—no Tigris-specific X-Tigris-Rename needed.

Different point on the spectrum, but less square-peg, also most probably much, much faster (it works great on linux-sized repos) :)