perf(frontend): Optimize component rendering with React.memo and hooks - Sprint 3 Story 2

Add React.memo to display components and useCallback/useMemo for better performance.

Changes:
- Added React.memo to TaskCard component
- Added React.memo to StoryCard component
- Added React.memo to KanbanBoard component
- Added React.memo to KanbanColumn component
- Added useCallback to kanban page drag handlers (handleDragStart, handleDragEnd)
- Added useCallback to epics page handlers (handleDelete, getStatusColor, getPriorityColor)
- Added useMemo for expensive computations in dashboard page (stats, recentProjects sorting)
- Added useMemo for total tasks calculation in KanbanBoard
- Removed unused isConnected variable from kanban page

Performance improvements:
- Reduced unnecessary re-renders in Card components
- Optimized list rendering performance with memoized callbacks
- Improved filtering and sorting performance with useMemo
- Better React DevTools Profiler metrics

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/(dashboard)/dashboard/page.tsx

@@ -1,7 +1,7 @@
 'use client';
 
 import Link from 'next/link';
-import { useState } from 'react';
+import { useState, useMemo } from 'react';
 import { Plus, FolderKanban, Archive, TrendingUp, ArrowRight } from 'lucide-react';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
 import { Button } from '@/components/ui/button';
@@ -15,16 +15,19 @@ export default function DashboardPage() {
   const { data: projects, isLoading } = useProjects();
 
   // Calculate statistics
-  const stats = {
+  const stats = useMemo(() => ({
     totalProjects: projects?.length || 0,
     activeProjects: projects?.length || 0, // TODO: Add status field to Project model
     archivedProjects: 0, // TODO: Add status field to Project model
-  };
+  }), [projects]);
 
   // Get recent projects (sort by creation time, take first 5)
-  const recentProjects = projects
-    ?.sort((a, b) => new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime())
+  const recentProjects = useMemo(() => {
+    return projects
+      ?.slice()
+      .sort((a, b) => new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime())
       .slice(0, 5) || [];
+  }, [projects]);
 
   return (
     <div className="space-y-8">

app/(dashboard)/projects/[id]/epics/page.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { use, useState } from 'react';
+import { use, useState, useCallback } from 'react';
 import Link from 'next/link';
 import { useRouter } from 'next/navigation';
 import {
@@ -62,7 +62,7 @@ export default function EpicsPage({ params }: EpicsPageProps) {
   const { data: epics, isLoading: epicsLoading, error } = useEpics(projectId);
   const deleteEpic = useDeleteEpic();
 
-  const handleDelete = async () => {
+  const handleDelete = useCallback(async () => {
     if (!deletingEpicId) return;
 
     try {
@@ -72,9 +72,9 @@ export default function EpicsPage({ params }: EpicsPageProps) {
       const message = error instanceof Error ? error.message : 'Failed to delete epic';
       toast.error(message);
     }
-  };
+  }, [deletingEpicId, deleteEpic]);
 
-  const getStatusColor = (status: WorkItemStatus) => {
+  const getStatusColor = useCallback((status: WorkItemStatus) => {
     switch (status) {
       case 'Backlog':
         return 'secondary';
@@ -87,9 +87,9 @@ export default function EpicsPage({ params }: EpicsPageProps) {
       default:
         return 'secondary';
     }
-  };
+  }, []);
 
-  const getPriorityColor = (priority: WorkItemPriority) => {
+  const getPriorityColor = useCallback((priority: WorkItemPriority) => {
     switch (priority) {
       case 'Low':
         return 'bg-blue-100 text-blue-700 hover:bg-blue-100';
@@ -102,7 +102,7 @@ export default function EpicsPage({ params }: EpicsPageProps) {
       default:
         return 'secondary';
     }
-  };
+  }, []);
 
   if (projectLoading || epicsLoading) {
     return (

app/(dashboard)/projects/[id]/kanban/page.tsx

@@ -8,7 +8,7 @@ import {
   DragStartEvent,
   closestCorners,
 } from '@dnd-kit/core';
-import { useState, useMemo } from 'react';
+import { useState, useMemo, useCallback } from 'react';
 import { useProjectStories } from '@/lib/hooks/use-stories';
 import { useEpics } from '@/lib/hooks/use-epics';
 import { useChangeStoryStatus } from '@/lib/hooks/use-stories';
@@ -43,7 +43,7 @@ export default function KanbanPage() {
 
   // SignalR real-time updates
   const queryClient = useQueryClient();
-  const { isConnected } = useSignalRConnection();
+  useSignalRConnection(); // Establish connection
   const changeStatusMutation = useChangeStoryStatus();
 
   // Subscribe to SignalR events for real-time updates
@@ -83,12 +83,12 @@ export default function KanbanPage() {
     Done: stories.filter((s) => s.status === 'Done'),
   }), [stories]);
 
-  const handleDragStart = (event: DragStartEvent) => {
+  const handleDragStart = useCallback((event: DragStartEvent) => {
     const story = stories.find((s) => s.id === event.active.id);
     setActiveStory(story || null);
-  };
+  }, [stories]);
 
-  const handleDragEnd = (event: DragEndEvent) => {
+  const handleDragEnd = useCallback((event: DragEndEvent) => {
     const { active, over } = event;
     setActiveStory(null);
 
@@ -101,7 +101,7 @@ export default function KanbanPage() {
       logger.debug(`[Kanban] Changing story ${story.id} status to ${newStatus}`);
       changeStatusMutation.mutate({ id: story.id, status: newStatus });
     }
-  };
+  }, [stories, changeStatusMutation]);
 
   if (isLoading) {
     return (

components/features/kanban/KanbanBoard.tsx

@@ -1,5 +1,6 @@
 'use client';
 
+import React, { useMemo } from 'react';
 import { TaskCard } from './TaskCard';
 import type { LegacyKanbanBoard } from '@/types/kanban';
 
@@ -9,13 +10,17 @@ interface KanbanBoardProps {
 
 // Legacy KanbanBoard component using old Kanban type
 // For new Issue-based Kanban, use the page at /projects/[id]/kanban
-export function KanbanBoard({ board }: KanbanBoardProps) {
+export const KanbanBoard = React.memo(function KanbanBoard({ board }: KanbanBoardProps) {
+  const totalTasks = useMemo(() => {
+    return board.columns.reduce((acc, col) => acc + col.tasks.length, 0);
+  }, [board.columns]);
+
   return (
     <div className="space-y-4">
       <div className="flex items-center justify-between">
         <h2 className="text-2xl font-bold">{board.projectName}</h2>
         <p className="text-sm text-muted-foreground">
-          Total tasks: {board.columns.reduce((acc, col) => acc + col.tasks.length, 0)}
+          Total tasks: {totalTasks}
         </p>
       </div>
       <div className="flex gap-4 overflow-x-auto pb-4">
@@ -48,4 +53,4 @@ export function KanbanBoard({ board }: KanbanBoardProps) {
       </p>
     </div>
   );
-}
+});

components/features/kanban/KanbanColumn.tsx

@@ -1,5 +1,6 @@
 'use client';
 
+import React from 'react';
 import { useDroppable } from '@dnd-kit/core';
 import { SortableContext, verticalListSortingStrategy } from '@dnd-kit/sortable';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
@@ -14,7 +15,7 @@ interface KanbanColumnProps {
   taskCounts?: Record<string, number>; // Map of storyId -> taskCount
 }
 
-export function KanbanColumn({ id, title, stories, epicNames = {}, taskCounts = {} }: KanbanColumnProps) {
+export const KanbanColumn = React.memo(function KanbanColumn({ id, title, stories, epicNames = {}, taskCounts = {} }: KanbanColumnProps) {
   const { setNodeRef } = useDroppable({ id });
 
   return (
@@ -47,4 +48,4 @@ export function KanbanColumn({ id, title, stories, epicNames = {}, taskCounts =
       </CardContent>
     </Card>
   );
-}
+});

components/features/kanban/StoryCard.tsx

@@ -1,5 +1,6 @@
 'use client';
 
+import React, { useMemo } from 'react';
 import { useSortable } from '@dnd-kit/sortable';
 import { CSS } from '@dnd-kit/utilities';
 import { Card, CardContent } from '@/components/ui/card';
@@ -7,7 +8,6 @@ import { Badge } from '@/components/ui/badge';
 import { Avatar, AvatarFallback } from '@/components/ui/avatar';
 import { Story } from '@/types/project';
 import { FileText, FolderKanban, Clock, CheckSquare } from 'lucide-react';
-import { useMemo } from 'react';
 
 interface StoryCardProps {
   story: Story;
@@ -15,7 +15,7 @@ interface StoryCardProps {
   taskCount?: number;
 }
 
-export function StoryCard({ story, epicName, taskCount }: StoryCardProps) {
+export const StoryCard = React.memo(function StoryCard({ story, epicName, taskCount }: StoryCardProps) {
   const { attributes, listeners, setNodeRef, transform, transition } =
     useSortable({ id: story.id });
 
@@ -140,4 +140,4 @@ export function StoryCard({ story, epicName, taskCount }: StoryCardProps) {
       </CardContent>
     </Card>
   );
-}
+});

components/features/kanban/TaskCard.tsx

@@ -1,5 +1,6 @@
 'use client';
 
+import React from 'react';
 import { Card, CardContent, CardHeader } from '@/components/ui/card';
 import { Clock, User } from 'lucide-react';
 import type { TaskCard as TaskCardType } from '@/types/kanban';
@@ -9,7 +10,7 @@ interface TaskCardProps {
   isDragging?: boolean;
 }
 
-export function TaskCard({ task, isDragging = false }: TaskCardProps) {
+export const TaskCard = React.memo(function TaskCard({ task, isDragging = false }: TaskCardProps) {
   const priorityColors = {
     Low: 'bg-blue-100 text-blue-700',
     Medium: 'bg-yellow-100 text-yellow-700',
@@ -59,4 +60,4 @@ export function TaskCard({ task, isDragging = false }: TaskCardProps) {
       </CardContent>
     </Card>
   );
-}
+});