A check's answer for one chain on one destination.
Type Declaration
"pass"
Fits, with everything resolved.
"fail"
Does not fit — the figure that decides it is known and over.
"unknown"
Cannot be decided: a figure is missing, or the known span straddles the limit. Never
silently a pass — an unknown is surfaced with the reason it is unknown.
A check's answer for one chain on one destination.