initialTopMostItemIndex was a plain index (top-aligned), so react-virtuoso painted with estimated row heights then corrected scrollTop after measuring the real (taller) dynamic bubbles — a visible jump on every chat switch. Use { index: 'LAST', align: 'end' } to pin the bottom edge instead, matching react-virtuoso's canonical chat pattern; the restore-to-saved-row path stays align: 'start'.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
byGalax
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