Make stick-to-bottom intent the single source of truth in MessageList and
drive onAtBottomChange from intent, not raw scroll position. A measurement
reflow can no longer flip the intent off (RC1), the second scrollPositions
writer no longer persists a drifting topmost index while stuck (RC2), and a
pin-on-rows layout effect re-pins through the two-phase data swap (RC3).
- scrollController: add tested nextStickIntent() state machine
- MessageList: input-event-based unstick (wheel/key/touch + scrollbar drag),
reveal after 2 stable frames, tabIndex for keyboard nav, remove debug overlay
- ConversationPage: reuse resolveInitialAnchor; harden handleRangeChanged
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
byGalax
b057795735