Hi Yurii,
I’m very glad you are interested in the SAFE project because the synergy that your decentralized Github project has with SAFE is remarkable (For anyone not familiar with Yurii’s project check out Gitchain on kickstarter)
Regarding your question - I know you are asking for formal specs but a good place to start is this blog post and the comment section below.
Another interesting resource is the System docs
But for a detailed and formal spec you are going to have to wait for the paper to come out (I think it should come out very soon but I’m in no way sure about this) or better yet you could ask @dirvine himself…
If he doesn’t respond here make sure to post on the dev mailing list
Also you should check out @chadrickm 's project Builder Hub since your projects also go perfectly hand in hand.