One command

One command, always the same, that leaves you oriented.

That is the whole reason for reaching for fathom at all, and it answers three things at once:

is this sound?	valid, whole, and free of silent damage
what is in here?	the structure folded to its shape, with the fold reported
what could one row be?	every defensible answer, and what each would cost

It is one verb rather than three because a diagnostic people can skip is a diagnostic people do skip.

The three chapters of this part are those three questions, in that order. The first two describe something that runs, and show it running. The third describes the half that is designed, prototyped and not yet in the core, and says so.