lit-virtualizer's flow layout has a scroll error correction mechanism that
calls scrollTo() to fix sub-pixel estimation errors. On large lists (20k+),
even with fixed-height items, floating-point differences from
getBoundingClientRect() (e.g. 49.000003px vs 49px) accumulate across items
and trigger corrections that fight the native scrollbar drag gesture,
causing the thumb to desync from the mouse.
Detect scrollbar drag by checking if mousedown occurs in the scrollbar
gutter (clientX > element clientWidth), then monkey-patch the virtualizer's
_correctScrollError method to discard accumulated errors during drag
instead of calling scrollTo(). Items continue to render/recycle normally
since layout updates are not suppressed -- only the scroll position
corrections are skipped.
yonlu
0bd8cefa00