artifact cache in git

[terabyte]

Y'know what git is really swell at? Storing immutable blobs of junk. Deduplicating those blobs. Indexing them. Synchronizing them. Unfortunately, trees cannot be labeled directly in git, it requires commit objects, but some sort of git-based artifact cache could save us a ton of storage space in our caches, since it is mostly just copies and copies on top of copies of the same damn third party jars all over.