ThreadTimeline's scroll compute read getBoundingClientRect for every user
message per scroll frame; interleaved with React's streaming style writes
each read forced a full reflow — the hottest self-time frame in the
multitab profile (620ms over one 5-tab run). While the viewport is pinned
to the bottom the active prompt is simply the last entry, so answer from
data and save the layout reads for actual scrollback.
Brooklyn Nicholson
982a425162