Entering a historical session sometimes showed a smooth scroll from a mid
position instead of landing instantly at the bottom. The single-writer change
had startFollowLoop stop the settle burst, so a content-measurement
ResizeObserver tick during restore would downgrade the authoritative instant
pin into an easing follow loop that scrolled in from the partially-measured
position.
- startFollowLoop now yields to an active settle burst instead of stopping it.
The asymmetry is intentional: the settle burst is the authoritative instant
pin (session restore / goToBottom 'instant') and must not be preempted by the
easing loop. startSettleBurst still stops the follow loop, so the two never
write scrollTop in the same frame.
- tickFollow snaps deltas larger than a full viewport (discrete jumps: late
history measurement, session entry, a big block in one commit) instead of
easing them; only small streaming-sized deltas ease.
- restoreSnapshot mirrors goToBottom('instant') — instant write + settle burst,
no startFollowLoop.
Bohdan Triapitsyn
3c3abd2afe