Sounds like a perfect fit for https://slatedb.io/ -- it's just that (an embedded, rust, KV store that supports transactions).

It's built specifically to run on object storage, currently relies on the `object_store` crate but we're consdering OpenDAL instead so if Garage works with those crates (I assume it does if its S3 compatible) it should just work OOTB.

for Garage's particular use case I think SlateDB's "backed by object storage" would be an anti-feature. their usage of LMDB/SQLite is for the metadata of the object store itself - trying to host that metadata within the object store runs into a circular dependency problem.