I feel like make/ninja suffer from the same output modstamp > input modstamps to rebuild. Really a build system should track modstmaps on all inputs (apps included), and the rebuild on not-equal.

Would be nice to see build2 go this route.

I did some exploration of this idea in a followup build system! See https://neugierig.org/software/blog/2022/03/n2.html . (It's not really production-ready.)