Tue Nov 27 11:39:30 EST 2018

trusting the incremental build

1. you are going to use the incremental build.  rebuilding requires
too much time in any practical system.

2. you will need to be able to trust it, because some of your
debugging experiments are going to rely on measuring the effect of
small changes.

getting the incremental build correct is just another debugging
problem, but how to actually specify it, or test its correctness?

basically, every time an edit is made and a command is sent to
propagate the current code state, it should be verified which files
actually changed using time stamp and content hash.