The core store layer is quite small, and I am trying to thoroughly document it, with all 3 of:

- a more "academic" spec of what it does

- nuts-and-bolts JSON schema for many data types

- JSON golden tests instead of C++ literals in the unit tests as often as possible.

I hope this will make additional store layer easy to churn out.

(The "hash derivation modulo" that is so fiddly described in this blog post can be dropped in a world where we no longer have input addressing, and just have content-addressing. Or, in a world where we have a new, simpler type of input-addressing instead.)