The residual flicker on chat switch was a loading/reveal artifact, not scroll.
listReady gated the MessageList reveal on reactionsReady OR a 300ms timeout, so
on a cache-hit switch (messages already present from the first render) the list
sat at opacity:0 for up to 300ms and then popped in. Drop the reactions/timeout
gate: reveal as soon as messages exist. Reaction chips stream in a beat later;
because the list is pinned to the bottom their height growth re-pins with no
visible jump, and MessageList still defers its own reveal a few frames until the
row-height measurement settles so it appears already at the final bottom.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
