perf(post-rendering): reduce quoted backlink rerenders via scoped store subscription

Replaced duplicated quotedByMap construction with useQuotedByMap() hook that subscribes only to post numbers referenced in each thread. Updated registerComments() to skip no-op writes, eliminating unnecessary numberToCid identity changes during feed scrolling.

src/hooks/use-quoted-by-map.ts

@@ -0,0 +1,99 @@
+import { useCallback, useMemo } from 'react';
+import { Comment } from '@plebbit/plebbit-react-hooks';
+import { QUOTE_NUMBER_REGEX } from '../lib/utils/url-utils';
+import usePostNumberStore from '../stores/use-post-number-store';
+
+interface ReplyQuoteTargets {
+  reply: Comment;
+  quotedPostNumbers: number[];
+}
+
+const extractReplyQuoteTargets = (replies: Comment[]) => {
+  const quotedPostNumbers = new Set<number>();
+  const replyQuoteTargets: ReplyQuoteTargets[] = [];
+
+  for (const reply of replies) {
+    const quotedPostNumbersForReply: number[] = [];
+
+    if (reply.content) {
+      for (const match of reply.content.matchAll(QUOTE_NUMBER_REGEX)) {
+        const postNumber = Number.parseInt(match[1], 10);
+        if (!Number.isNaN(postNumber)) {
+          quotedPostNumbersForReply.push(postNumber);
+          quotedPostNumbers.add(postNumber);
+        }
+      }
+    }
+
+    replyQuoteTargets.push({
+      reply,
+      quotedPostNumbers: quotedPostNumbersForReply,
+    });
+  }
+
+  return {
+    replyQuoteTargets,
+    quotedPostNumbers: [...quotedPostNumbers].sort((a, b) => a - b),
+  };
+};
+
+const useQuotedByMap = (replies: Comment[] = []) => {
+  const { replyQuoteTargets, quotedPostNumbers } = useMemo(() => extractReplyQuoteTargets(replies), [replies]);
+
+  // Subscribe only to post numbers referenced in this thread to avoid unrelated global store churn.
+  const quotedNumbersSignature = usePostNumberStore(
+    useCallback((state) => quotedPostNumbers.map((postNumber) => `${postNumber}:${state.numberToCid[postNumber] ?? ''}`).join('|'), [quotedPostNumbers]),
+  );
+
+  const quotedNumberToCid = useMemo(() => {
+    if (quotedPostNumbers.length === 0) {
+      return {} as Record<number, string>;
+    }
+
+    const { numberToCid } = usePostNumberStore.getState();
+    const nextQuotedNumberToCid: Record<number, string> = {};
+
+    for (const postNumber of quotedPostNumbers) {
+      const quotedCid = numberToCid[postNumber];
+      if (quotedCid) {
+        nextQuotedNumberToCid[postNumber] = quotedCid;
+      }
+    }
+
+    return nextQuotedNumberToCid;
+  }, [quotedPostNumbers, quotedNumbersSignature]);
+
+  return useMemo(() => {
+    const map = new Map<string, Comment[]>();
+
+    for (const { reply, quotedPostNumbers: quotedNumbersForReply } of replyQuoteTargets) {
+      const cidSet = new Set<string>();
+
+      if (reply.quotedCids?.length) {
+        for (const quotedCid of reply.quotedCids) {
+          cidSet.add(quotedCid);
+        }
+      }
+
+      for (const postNumber of quotedNumbersForReply) {
+        const quotedCid = quotedNumberToCid[postNumber];
+        if (quotedCid) {
+          cidSet.add(quotedCid);
+        }
+      }
+
+      for (const quotedCid of cidSet) {
+        const repliesQuotingCid = map.get(quotedCid);
+        if (repliesQuotingCid) {
+          repliesQuotingCid.push(reply);
+        } else {
+          map.set(quotedCid, [reply]);
+        }
+      }
+    }
+
+    return map;
+  }, [replyQuoteTargets, quotedNumberToCid]);
+};
+
+export default useQuotedByMap;