content-visibility:auto on turn groups (perf: off-screen turns skip
style/layout/paint) pairs with contain-intrinsic-size:auto, which only
remembers a turn's size after it renders. A turn that finished streaming
near the bottom had its smaller mid-stream size remembered; once it
scrolled off the top edge and got skipped, it collapsed to that stale
height. With overflow-anchor:none the viewport can't self-correct, so the
stick-to-bottom lock drifts and the view creeps up over older turns — the
'long session eventually shows old responses' visual glitch.
Exempt the newest turns (live tail) from virtualization so a turn is only
ever skipped after its layout has settled at its final size (remembered ==
real -> skipping changes no height). Off-screen older turns still skip, so
the dialog/popover whole-document recalc win on long transcripts is kept
(it scales with the hundreds of old turns, not the small tail).
brooklyn!
3de91c6974