that's very interesting, thank you, i should have realized that even early on there had to be a way to share code between images. (and i don't know why i missed that comment before responding myself)

but, doesn't building a new system image involve taking an old/existing image, adding/merging all the changes, and then release new image and sources file from that?

in other words, the image is not recreated from scratch every time and it is more than just a cache.

what is described there is the process of source management in the absence of a proper revision control system. obviously when multiple people work on the same project, somewhere the changes need to be tracked and merged.

but that doesn't change the fact that the changes first happen in an image, and that you could save that image and write out a new sources file.