Android - FlashList briefly goes blank during fast scroll on Inbox and Reports > Expenses (verify fixed with LegendList) #99202

Problem

On Android, the FlashList used by Inbox and Reports > Expenses briefly goes blank during fast flings. Both lists use drawDistance={250}, which FlashList turns into only ~350 px of directional pre-render buffer on the tested 727 px viewport. Captured fast flings moved 558–917 px in 114–178 ms, so the viewport outruns the rendered cells and momentarily reaches zero viewable items — the list shows blank until FlashList catches up.

This is a known tradeoff from #82378 and #83277, which reduced the prior 1000 px buffer for performance. #83277 explicitly noted that fast scrolling could show blank spaces.

Context

We're migrating these lists to LegendList, so we intentionally do not want to add more work in FlashList for this. This issue exists to make sure the fast-scroll blanking is fixed once LegendList is in place — i.e. verify LegendList keeps the list continuously rendered through fast Android flings on Inbox and Reports > Expenses.

Reproduction

1. On Android, open Inbox (or Reports > Expenses) with a long list.
2. Fast-fling scroll through the list.
3. Observe the list briefly going blank until it catches up.

Notes

• An Android-only drawDistance={1000} candidate kept the list continuously rendered through repeated Inbox and Reports > Expenses tests (test branch: https://github.com/KJ21-ENG/App/tree/KJ21-ENG/android-flashlist-fast-scroll-blanking) — but this is FlashList-specific and not the intended fix given the LegendList migration.
• Originally reported by KJ21-ENG in Backport missing ViewState guards for state and padding updates #98869 (comment).