The current algorithm is so trivial and lame that I didn't even bother :) I'll add some docs in the next batch.

I don't know what else you expect in the doc comment for DriverComputation as it seems to already describe just that:

/** Represents a computation that needs to be performed by another driver.
  * Despite having a child it is a NullaryNode because the sub-computation
  * should be opaque to the query compiler. */