Two ResizeObserver effects (content and container) each had their own
local restoreGuardRafId but both wrote to the shared
isRestoringScrollRef. Either observer's guard-clear RAF could fire
while the other's pin chain was in-flight, leaving isRestoringScrollRef
prematurely false.
scrollTranscriptToBottom also set isRestoringScrollRef without
cancelling any pending guard-clear, so a stale clear could drop
the flag mid-smooth-scroll animation.
Promote restoreGuardRafId to a single shared ref so all write
paths coordinate through one cancellation point.
Mathias Fredriksson
d2c308e481