perf(replies): progressive render, 500 replies/page, content-visibility

Set repliesPerPage to 500 to avoid Virtuoso pagination sort drift. Add useProgressiveRender with startTransition batching and CSS content-visibility for long reply lists.

src/components/post-mobile/post-mobile.tsx

@@ -37,6 +37,8 @@ import useFeedResetStore from '../../stores/use-feed-reset-store';
 import usePostNumberStore from '../../stores/use-post-number-store';
 import { alertChallengeVerificationFailed } from '../../lib/utils/challenge-utils';
 import useQuotedByMap from '../../hooks/use-quoted-by-map';
+import useProgressiveRender from '../../hooks/use-progressive-render';
+import { REPLIES_PER_PAGE } from '../../lib/constants';
 
 const { addChallenge } = useChallengesStore.getState();
 
@@ -497,6 +499,7 @@ const PostMobile = ({
     comment: post,
     sortType: 'old',
     flat: true,
+    repliesPerPage: REPLIES_PER_PAGE,
     accountComments: { newerThan: Infinity, append: true },
   });
   const { replies, hasMore, loadMore } = repliesResult;
@@ -537,6 +540,13 @@ const PostMobile = ({
 
   const quotedByMap = useQuotedByMap(filteredReplies);
 
+  const visibleReplies = useProgressiveRender(filteredReplies, {
+    batchSize: 50,
+    intervalMs: 100,
+    resetKey: cid,
+    disabled: hasMore || !!targetReplyCid || !showAllReplies,
+  });
+
   // Virtuoso scroll position management for infinite replies
   const virtuosoRef = useRef<VirtuosoHandle | null>(null);
   const virtuosoStateKey = `replies-mobile-${cid}`;
@@ -670,7 +680,7 @@ const PostMobile = ({
               !isInPendingPostView &&
               showReplies &&
               !hasMore &&
-              filteredReplies.map((reply, index) => (
+              visibleReplies.map((reply, index) => (
                 <div key={index} className={styles.replyContainer}>
                   <Reply postReplyCount={replyCount} reply={reply} roles={roles} threadNumber={post?.number} quotedByMap={quotedByMap} />
                 </div>