Purify the recursive resolver

[barrucadu]

The recursive resolver is awkward to test because it mixes network calls with business logic. So I just don't test it right now. I test the things it uses, but not it directly. This is a shame, as the recursive resolver is nontrivial.

Purifying it somehow - either making it return some state object and handling the network calls & iteration from a very small function outside it which can easily be eyeballed, or by passing in some "network handle" which can be mocked (ew) - would let me directly test it.