Reduce window size for adjacent but never-focused feed pages

Track whether each feed page has been focused at least once. For
adjacent pages that are only prefetching (never viewed by the user),
use windowSize=1 to minimize rendering overhead. Once a page has
been focused, it keeps the default windowSize=9 for smooth swiping.

https://claude.ai/code/session_01SJL2SqcPnJo7wbhku6SFt5

src/view/com/feeds/FeedPage.tsx

@@ -75,6 +75,10 @@ export function FeedPage({
   const feedFeedback = useFeedFeedback(feedInfo, hasSession)
   const scrollElRef = useRef<ListMethods>(null)
   const [hasNew, setHasNew] = useState(false)
+  const [hasBeenFocused, setHasBeenFocused] = useState(isPageFocused)
+  if (isPageFocused && !hasBeenFocused) {
+    setHasBeenFocused(true)
+  }
   const setHomeBadge = useSetHomeBadge()
   const isVideoFeed = useMemo(() => {
     const isBskyVideoFeed = VIDEO_FEED_URIS.includes(feedInfo.uri)
@@ -138,6 +142,8 @@ export function FeedPage({
   }, [ax, scrollToTop, feed, queryClient])
 
   const shouldPrefetch = IS_NATIVE && isPageAdjacent
+  const windowSize =
+    isPageAdjacent && !hasBeenFocused ? 1 : undefined
   const isDiscoverFeed = feedInfo.uri === DISCOVER_FEED_URI
   return (
     <View
@@ -161,6 +167,7 @@ export function FeedPage({
             headerOffset={headerOffset}
             savedFeedConfig={savedFeedConfig}
             isVideoFeed={isVideoFeed}
+            windowSize={windowSize}
           />
         </FeedFeedbackProvider>
       </MainScrollProvider>

src/view/com/posts/PostFeed.tsx

@@ -203,6 +203,7 @@ let PostFeed = ({
   savedFeedConfig,
   initialNumToRender: initialNumToRenderOverride,
   isVideoFeed = false,
+  windowSize: windowSizeOverride,
 }: {
   feed: FeedDescriptor
   feedParams?: FeedParams
@@ -225,6 +226,7 @@ let PostFeed = ({
   savedFeedConfig?: AppBskyActorDefs.SavedFeed
   initialNumToRender?: number
   isVideoFeed?: boolean
+  windowSize?: number
   lastFetchDate?: () => number
 }): React.ReactNode => {
   const ax = useAnalytics()
@@ -1015,7 +1017,7 @@ let PostFeed = ({
           desktopFixedHeightOffset ? desktopFixedHeightOffset : true
         }
         initialNumToRender={initialNumToRenderOverride ?? initialNumToRender}
-        windowSize={9}
+        windowSize={windowSizeOverride ?? 9}
         maxToRenderPerBatch={IS_IOS ? 5 : 1}
         updateCellsBatchingPeriod={40}
         onItemSeen={onItemSeen}