Hysteresis step: from currentKeep, move to the target fraction only when
the EFFECTIVE density (elementsPerPixel × currentKeep) has left the
[cap × leaveRatio, cap × enterRatio] band in the direction of the
target; otherwise hold. elementsPerPixel is the UNTHINNED density (the
tracker divides the node's full visible count by its footprint).
Hysteresis step: from
currentKeep, move to the target fraction only when the EFFECTIVE density (elementsPerPixel × currentKeep) has left the[cap × leaveRatio, cap × enterRatio]band in the direction of the target; otherwise hold.elementsPerPixelis the UNTHINNED density (the tracker divides the node's full visible count by its footprint).