Transforms on the chat scroller (content or container) forced WebKit to
rebuild its composited scrolling layers — a multi-second stall on long
chats. The scroller now gets no transforms at all: it keeps a constant
client height by extending below its shrunken region (by keyboard minus
the safe inset the shell gives up, so the settle snap is geometry-neutral)
and converting the keyboard strip into its own bottom padding, driven by
--oc-kb-scroll-inset from the very start of the rise. Nothing resizes for
the virtualizer, every reachable row stays mounted, and open/close is a
single cheap scrollTop write: the re-pin happens as the keyboard starts
rising, and the hide clamp lands behind the still-visible keyboard.
The composer and draft title keep sliding with the keyboard, now via
inline transforms set by the choreography — WebKit does not reliably
start transitions when a transform changes through a CSS custom property,
which had parked the composer until the keyboard finished.
Bohdan Triapitsyn
2c220f3c52