Disable follow-mode virtualization churn and simplify reasoning header layout so streaming thinking blocks stop nudging the scroll position while the list is pinned to bottom.
Keep visible rows mounted during follow-up measurements and clear stale refs so async message rendering no longer flickers or measures detached blocks. Coalesce per-item render notifications so content-heavy rows only trigger one remeasurement per frame.
Reverse the message stream scroll layout so the viewport naturally starts at the newest messages and keeps older content virtualized. Use sentinel-based edge chasing to make jump-to-top/bottom land reliably despite VirtualItem mounts.
Add DOM instrumentation tags and harden VirtualItem visibility for hidden/zero-sized roots to prevent inactive instances from keeping heavy tool-call markup mounted; restore message stream virtualization margin.
