feat: refactor ActivityTimeline and TaskCommentsSection to utilize useNewItemKeys hook

- Replaced manual tracking of new item keys in ActivityTimeline and TaskCommentsSection with a new custom hook, useNewItemKeys, for improved code clarity and reusability.
- Simplified state management related to new items in both components, enhancing maintainability and reducing complexity.
- Updated related logic to ensure consistent handling of newly visible items during pagination and resets.

src/renderer/components/team/activity/ActivityTimeline.tsx

@@ -7,6 +7,7 @@ import { AnimatedHeightReveal } from './AnimatedHeightReveal';
 import { ActivityItem, isNoiseMessage } from './ActivityItem';
 import { findNewestMessageIndex, resolveTimelineCollapseState } from './collapseState';
 import { groupTimelineItems, isLeadThought, LeadThoughtsGroupRow } from './LeadThoughtsGroup';
+import { useNewItemKeys } from './useNewItemKeys';
 
 import type { TimelineItem } from './LeadThoughtsGroup';
 import type { ActivityCollapseState } from './collapseState';
@@ -145,11 +146,6 @@ export const ActivityTimeline = ({
 }: ActivityTimelineProps): React.JSX.Element => {
   const [visibleCount, setVisibleCount] = useState(MESSAGES_PAGE_SIZE);
 
-  // --- New-message animation tracking ---
-  const knownKeysRef = useRef<Set<string>>(new Set<string>());
-  const isInitializedRef = useRef(false);
-  const prevVisibleCountRef = useRef(visibleCount);
-
   const colorMap = members ? buildMemberColorMap(members) : new Map<string, string>();
   const memberInfo = new Map<string, { role?: string; color?: string }>();
   if (members) {
@@ -243,32 +239,11 @@ export const ActivityTimeline = ({
     return timelineItems.map(getItemKey);
   }, [timelineItems]);
 
-  const isPaginationExpansion =
-    isInitializedRef.current && visibleCount > prevVisibleCountRef.current;
-
-  const newItemKeys = useMemo(() => {
-    if (!isInitializedRef.current || isPaginationExpansion) {
-      return new Set<string>();
-    }
-
-    const newKeys = new Set<string>();
-    for (const key of timelineItemKeys) {
-      if (!knownKeysRef.current.has(key)) {
-        newKeys.add(key);
-      }
-    }
-    return newKeys;
-  }, [isPaginationExpansion, timelineItemKeys]);
-
-  useEffect(() => {
-    if (!isInitializedRef.current) {
-      isInitializedRef.current = true;
-    }
-    for (const key of timelineItemKeys) {
-      knownKeysRef.current.add(key);
-    }
-    prevVisibleCountRef.current = visibleCount;
-  }, [timelineItemKeys, visibleCount]);
+  const newItemKeys = useNewItemKeys({
+    itemKeys: timelineItemKeys,
+    paginationKey: visibleCount,
+    resetKey: teamName,
+  });
 
   const handleShowMore = (): void => {
     setVisibleCount((prev) => prev + MESSAGES_PAGE_SIZE);

src/renderer/components/team/activity/useNewItemKeys.ts

@@ -0,0 +1,56 @@
+import { useEffect, useMemo, useRef } from 'react';
+
+interface UseNewItemKeysOptions {
+  itemKeys: string[];
+  paginationKey?: number;
+  resetKey?: string;
+}
+
+/**
+ * Tracks which currently visible items are newly mounted since the last committed render.
+ * Pagination expansions are treated as non-animated so "Show more" does not replay enter motion.
+ */
+export function useNewItemKeys({
+  itemKeys,
+  paginationKey = 0,
+  resetKey,
+}: UseNewItemKeysOptions): Set<string> {
+  const knownKeysRef = useRef<Set<string>>(new Set());
+  const isInitializedRef = useRef(false);
+  const prevPaginationKeyRef = useRef(paginationKey);
+
+  useEffect(() => {
+    knownKeysRef.current = new Set();
+    isInitializedRef.current = false;
+    prevPaginationKeyRef.current = paginationKey;
+  }, [resetKey]);
+
+  const isPaginationExpansion =
+    isInitializedRef.current && paginationKey > prevPaginationKeyRef.current;
+
+  const newItemKeys = useMemo(() => {
+    if (!isInitializedRef.current || isPaginationExpansion) {
+      return new Set<string>();
+    }
+
+    const next = new Set<string>();
+    for (const key of itemKeys) {
+      if (!knownKeysRef.current.has(key)) {
+        next.add(key);
+      }
+    }
+    return next;
+  }, [isPaginationExpansion, itemKeys]);
+
+  useEffect(() => {
+    if (!isInitializedRef.current) {
+      isInitializedRef.current = true;
+    }
+    for (const key of itemKeys) {
+      knownKeysRef.current.add(key);
+    }
+    prevPaginationKeyRef.current = paginationKey;
+  }, [itemKeys, paginationKey]);
+
+  return newItemKeys;
+}

src/renderer/components/team/dialogs/TaskCommentsSection.tsx

@@ -1,9 +1,10 @@
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
+import { useCallback, useEffect, useMemo, useState } from 'react';
 
 import { CopyButton } from '@renderer/components/common/CopyButton';
 import { MarkdownViewer } from '@renderer/components/chat/viewers/MarkdownViewer';
 import { AnimatedHeightReveal } from '@renderer/components/team/activity/AnimatedHeightReveal';
 import { ReplyQuoteBlock } from '@renderer/components/team/activity/ReplyQuoteBlock';
+import { useNewItemKeys } from '@renderer/components/team/activity/useNewItemKeys';
 import { ImageLightbox } from '@renderer/components/team/attachments/ImageLightbox';
 import { MemberBadge } from '@renderer/components/team/MemberBadge';
 import { ExpandableContent } from '@renderer/components/ui/ExpandableContent';
@@ -90,9 +91,6 @@ export const TaskCommentsSection = ({
   const [replyTo, setReplyTo] = useState<{ author: string; text: string } | null>(null);
   const [visibleCount, setVisibleCount] = useState(INITIAL_VISIBLE_COMMENTS);
   const [previewImageUrl, setPreviewImageUrl] = useState<string | null>(null);
-  const knownCommentIdsRef = useRef<Set<string>>(new Set());
-  const isInitializedRef = useRef(false);
-  const prevVisibleCountRef = useRef(INITIAL_VISIBLE_COMMENTS);
 
   // Reset local UI state when team/task changes.
   useEffect(() => {
@@ -100,9 +98,6 @@ export const TaskCommentsSection = ({
     setVisibleCount(INITIAL_VISIBLE_COMMENTS);
     setReplyTo(null);
     setPreviewImageUrl(null);
-    knownCommentIdsRef.current = new Set();
-    isInitializedRef.current = false;
-    prevVisibleCountRef.current = INITIAL_VISIBLE_COMMENTS;
   }, [teamName, taskId]);
 
   const draft = useDraftPersistence({ key: `taskComment:${teamName}:${taskId}` });
@@ -130,33 +125,11 @@ export const TaskCommentsSection = ({
     () => visibleComments.map((comment) => comment.id),
     [visibleComments]
   );
-
-  const isPaginationExpansion =
-    isInitializedRef.current && visibleCount > prevVisibleCountRef.current;
-
-  const newCommentIds = useMemo(() => {
-    if (!isInitializedRef.current || isPaginationExpansion) {
-      return new Set<string>();
-    }
-
-    const next = new Set<string>();
-    for (const id of visibleCommentIds) {
-      if (!knownCommentIdsRef.current.has(id)) {
-        next.add(id);
-      }
-    }
-    return next;
-  }, [isPaginationExpansion, visibleCommentIds]);
-
-  useEffect(() => {
-    if (!isInitializedRef.current) {
-      isInitializedRef.current = true;
-    }
-    for (const id of visibleCommentIds) {
-      knownCommentIdsRef.current.add(id);
-    }
-    prevVisibleCountRef.current = visibleCount;
-  }, [visibleCommentIds, visibleCount]);
+  const newCommentIds = useNewItemKeys({
+    itemKeys: visibleCommentIds,
+    paginationKey: visibleCount,
+    resetKey: `${teamName}:${taskId}`,
+  });
 
   const mentionSuggestions = useMemo<MentionSuggestion[]>(
     () =>