fix(filmstrip): sync remoteParticipants between itemKey and ThumbnailWrapper

Filmstrip._gridItemKey and _listItemKey reference this.props._remoteParticipants
(captured at the parent's render time), but ThumbnailWrapper._mapStateToProps
independently reads state['features/filmstrip'].remoteParticipants from Redux.
When a participant joins or leaves between the parent render and the child's
selector call, the two arrays can diverge, causing a tile keyed for participant A
to actually render participant B's video.

Pass _remoteParticipants through react-window's itemData so that
ThumbnailWrapper uses the same array snapshot that the itemKey functions use,
eliminating the race condition.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: isouvezz

react/features/filmstrip/components/web/Filmstrip.tsx

@@ -996,6 +996,7 @@ class Filmstrip extends PureComponent <IProps, IState> {
             _filmstripWidth,
             _hasScroll,
             _isVerticalFilmstrip,
+            _remoteParticipants,
             _remoteParticipantsLength,
             _resizableFilmstrip,
             _rows,
@@ -1020,7 +1021,7 @@ class Filmstrip extends PureComponent <IProps, IState> {
                     height = { _filmstripHeight }
                     initialScrollLeft = { 0 }
                     initialScrollTop = { 0 }
-                    itemData = {{ filmstripType }}
+                    itemData = {{ filmstripType, remoteParticipants: _remoteParticipants }}
                     itemKey = { this._gridItemKey }
                     onItemsRendered = { this._onGridItemsRendered }
                     overscanRowCount = { 1 }
@@ -1039,6 +1040,7 @@ class Filmstrip extends PureComponent <IProps, IState> {
             itemCount: _remoteParticipantsLength,
             className: `filmstrip__videos remote-videos ${_resizableFilmstrip ? '' : 'height-transition'}`,
             height: _filmstripHeight,
+            itemData: { remoteParticipants: _remoteParticipants },
             itemKey: this._listItemKey,
             itemSize: 0,
             onItemsRendered: this._onListItemsRendered,

react/features/filmstrip/components/web/ThumbnailWrapper.tsx

@@ -136,7 +136,7 @@ class ThumbnailWrapper extends Component<IProps> {
  * @returns {IProps}
  */
 function _mapStateToProps(state: IReduxState, ownProps: { columnIndex: number;
-    data: { filmstripType: string; }; index?: number; rowIndex: number; }) {
+    data: { filmstripType: string; remoteParticipants?: string[]; }; index?: number; rowIndex: number; }) {
     const _currentLayout = getCurrentLayout(state);
     const { remoteParticipants: remote } = state['features/filmstrip'];
     const activeParticipants = getActiveParticipantsIds(state);
@@ -145,7 +145,16 @@ function _mapStateToProps(state: IReduxState, ownProps: { columnIndex: number;
     const filmstripType = ownProps.data?.filmstripType;
     const stageFilmstrip = filmstripType === FILMSTRIP_TYPE.STAGE;
     const sortedActiveParticipants = activeParticipants.sort();
-    const remoteParticipants = stageFilmstrip ? sortedActiveParticipants : remote;
+
+    // Use the remoteParticipants snapshot passed via itemData to ensure
+    // consistency with Filmstrip's itemKey functions, which reference
+    // the same array from the parent's render cycle. Reading directly
+    // from Redux could yield a newer array if the store updated between
+    // the parent render and this selector call, causing key/participant
+    // mismatches (wrong video shown in a tile).
+    const remoteParticipants = stageFilmstrip
+        ? sortedActiveParticipants
+        : (ownProps.data?.remoteParticipants ?? remote);
     const remoteParticipantsLength = remoteParticipants.length;
     const localId = getLocalParticipant(state)?.id;