ifd requires building which uses async code today, fetching requires
network io which really should use async code but does not yet. eval
itself cannot be made async for performance reasons. offloading work
to other threads is possible but questionable as currently there are
no uses in which evaluation must take place from within asynchronous
operations, which are currently confined entirely to store behavior.
Change-Id: I1e3c86fca19b042d79332e9a5ef9546f90a6448b
eldritch horrors
d6a203b795