Function built 

pub fn built() -> u64

How many columns this process has built.

docs/08 §8.3 item 9’s half of the same obligation as the switch above: a choice made unbidden should be answerable after the fact. This is the smallest honest answer — not which list, but whether the layout is reaching anything at all — and it is what lets a sweep say “the corpus builds none” rather than leaving that to be assumed.

Counted where a column is created: a pack that found one, or a push that promoted an empty list. Not per element, and never on the boxed path.