The scroll controller disengaged auto-follow purely by position: a single
scroll event had to land more than 24px above the bottom. During heavy
output the renderer re-pins to the bottom every frame, so each increment
of a slow upward drag restarted from the bottom and never beat the
tolerance - the view snapped back down every few milliseconds.

Disengage on direction instead: any upward scroll that leaves content
below flips to holding on the first tick, before the next frame's pin.
The one non-user upward move is preserved - a content shrink (row
eviction, clear) clamps scrollTop to the new bottom and keeps following.