fix(filmstrip): sync remoteParticipants between itemKey and ThumbnailWrapper

[JangJuMyeong]

Summary

Fixes a race condition where the wrong participant's video is displayed in a tile. Filmstrip._gridItemKey / _listItemKey and ThumbnailWrapper._mapStateToProps each independently read remoteParticipants — the former from this.props (captured at the parent's render time), the latter directly from Redux state. When a participant joins or leaves between these two reads, the arrays diverge: a tile keyed for participant A ends up rendering participant B's video.

How we found it

We operate a customized Jitsi Meet deployment serving ~200 users, where a manager oversees up to 50 participants simultaneously in tile view. With frequent join/leave activity at that scale, the mismatch became consistently reproducible.

Root cause

react-window renders child components (ThumbnailWrapper) independently from the parent (Filmstrip). The parent's itemKey callback captures _remoteParticipants from its own render-cycle props, but ThumbnailWrapper._mapStateToProps reads a potentially newer snapshot from Redux. If the store updates between these two reads, index-to-participant mapping breaks.

Fix

Pass _remoteParticipants through react-window's itemData prop so that ThumbnailWrapper uses the same array snapshot as the itemKey functions. This is the intended use of itemData — sharing parent-scoped data with virtualized children.

Test plan

• Join a tile-view call with 3+ participants
• Have participants rapidly join and leave
• Verify each tile consistently shows the correct participant's video and name

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[JangJuMyeong]

Hi, I've just signed the ICLA. Thanks for the heads up!