You’d expect that while the frontier of changes fans out and grows, some of them burn out and disappear and some of them survive and solidify into a relatively static code base.

The big baddies of build have worked this way for a long time already. Git surfaces a single Merkle tree id for the whole repo on each commit, but build tools like bazel/blaze, buck, pants, et al look at hashes of subtrees and use cached artifacts for the parts of the tree that didn’t change.

Your CI no longer becomes a binary signal on the code and more of a continuous signal on how much your “this works” pointer has caught up with your “this is the latest code” pointer.