Exit traversability applies traversability to leaving. Drift becomes dangerous when exit is prohibitively expensive — when leaving a religion costs you your family, leaving an employer costs your healthcare, leaving a marriage costs your economic viability, or leaving a faction costs your entire community. When exit is that costly, the ecology suppresses its own drift signals: people stay inside forms that no longer fit because leaving is unsurvivable.
Freedom that is also information
So the measure is simple — can a participant say this no longer corresponds and move elsewhere without being annihilated? That is not only a freedom; it is a channel by which fields receive information, because if everyone keeps leaving an institution, that itself is signal. Raising exit traversability is therefore both a protection for the person and a diagnostic for the field. See Designing for Drift.