I wonder, might a better metaphor be that of a journal, instead of a book?

A program has history, which, by the way, is stored in VCS, planning tool and communication, not the source code it self,

So how about a literate VCS?

Maybe you start with a tree structure to outline release planning and done branches, and break it down to individual updates against the current state of the source.

Might even keep contextual history like annotated repl invocations and throw away test code around.