Lighthouse Frontend Engineer

Expert knowledge of frontend patterns and architecture for the Lighthouse Journey Timeline.

🏗️ Core Architecture

Technology Stack

• Framework: React 18 with TypeScript
• State Management:
  • Server State: TanStack Query (React Query)
  • Client State: Zustand with devtools middleware
  • URL State: wouter (useLocation, useSearchPageQuery)
• Routing: wouter (lightweight React router)
• Styling: Tailwind CSS + lucide-react icons
• Forms: react-hook-form + Zod validation
• Testing: Vitest + React Testing Library + MSW v2
• HTTP Client: Custom fetch wrapper with credentials

Data Flow Architecture

Component (React)
    ↓
State Decision:
├── Server Data → TanStack Query Hook → API Service → fetch (credentials)
│                      ↓
│                 Type-Safe Response (@journey/schema/api)
│
└── UI State → Zustand Store (devtools)
    ↓
Type-Safe Types (from @journey/schema)

Key Flow:

1. Component calls TanStack Query hook
2. Hook uses API service layer
3. API service uses fetch with credentials: "include"
4. Request/Response types from @journey/schema/src/api/
5. UI state (selections, UI flags) in Zustand
6. Server state (data, caching) in TanStack Query

📍 CRITICAL: Where to Look Before Making Changes

Pattern References (ALWAYS CHECK THESE FIRST)

Pattern	Primary Reference	Secondary Reference
Reusable Components	packages/components/src/	ALWAYS CHECK FIRST
API Types (Request/Response)	packages/schema/src/api/	CHECK HERE FIRST
API Service Layer	packages/ui/src/services/	Type-safe API calls
TanStack Query Hook	packages/ui/src/hooks/search/useSearchPageQuery.ts	Query patterns, URL state
Zustand Store	packages/ui/src/stores/search-store.ts	UI state management
Query Client Setup	packages/ui/src/lib/queryClient.ts	Global config, fetch wrapper
Token Manager	packages/ui/src/services/token-manager.ts	JWT storage, singleton pattern
Component Test	packages/ui/src/components/nodes/shared/InsightCard.test.tsx	Testing patterns with MSW
Form Patterns	packages/ui/src/components/nodes/job/JobModal.tsx	react-hook-form + Zod
Domain Types	packages/schema/src/types.ts	Shared type definitions
MSW Handlers	packages/ui/src/mocks/profile-handlers.ts	API mocking patterns
Side Panel Component	packages/ui/src/components/timeline/NetworkInsightsSidePanel.tsx	Figma-based component design

⚡ Type Safety & Validation

🎯 CRITICAL: Use Enums and Constants, Not Magic Strings

Never use magic strings. Always use enums, constants, or Zod enums for:

• API endpoints: Define in constants file, not inline
• Node types: Use z.nativeEnum(TimelineNodeType) from shared schema
• Status values: Use Zod enums for validation + type inference
• Action types: Use string literal unions or enums
• Route paths: Define as constants with params
• Storage keys: Define as const object, not inline strings

Example - Route Constants:

// ✅ GOOD: Constants file
export const ROUTES = {
  TIMELINE: '/timeline',
  SEARCH: '/search',
  NODE_DETAIL: (id: string) => `/timeline/${id}`,
} as const;

// Usage
navigate(ROUTES.NODE_DETAIL(nodeId));

// ❌ BAD: Magic strings
navigate(`/timeline/${nodeId}`);

Example - Zod Enums:

// ✅ GOOD: Shared enum from schema
import { TimelineNodeType } from '@journey/schema';
const NodeTypeSchema = z.nativeEnum(TimelineNodeType);

// ✅ GOOD: String literal union
const StatusSchema = z.enum(['draft', 'published', 'archived']);
type Status = z.infer<typeof StatusSchema>;

// ❌ BAD: Plain strings
type Status = string;

OpenAPI → TypeScript Types Workflow

0. Generate/Update Types from OpenAPI (When API Changes)

# From packages/server directory
pnpm generate:swagger  # Updates openapi-schema.yaml

# Manual type creation in packages/schema based on OpenAPI
# TODO: Add automated OpenAPI → TypeScript generator when available

1. Check/Create Types in @journey/schema

// packages/schema/src/types.ts

// Generate from OpenAPI schema
export interface CreateNodeRequest {
  type: TimelineNodeType;
  parentId?: string;
  meta: {
    title: string;
    company?: string;
    startDate: string;
    endDate?: string;
  };
}

// Create Zod schema for validation
export const CreateNodeRequestSchema = z.object({
  type: z.nativeEnum(TimelineNodeType),
  parentId: z.string().uuid().optional(),
  meta: z.object({
    title: z.string().min(1).max(200),
    company: z.string().optional(),
    startDate: z.string().datetime(),
    endDate: z.string().datetime().optional(),
  }),
});

// Infer type from schema
export type CreateNodeRequestDTO = z.infer<typeof CreateNodeRequestSchema>;

2. Use Types in API Service

// packages/ui/src/services/hierarchy-api.ts
import { CreateNodeRequestDTO, CreateNodeRequestSchema } from '@journey/schema';

export async function createNode(data: CreateNodeRequestDTO) {
  // Validate at runtime
  const validated = CreateNodeRequestSchema.parse(data);

  return httpClient.post<NodeResponse>('/api/v2/timeline/nodes', validated);
}

3. Consume in Component

// Component using the API
import { CreateNodeRequestDTO } from '@journey/schema';

const onSubmit = async (data: CreateNodeRequestDTO) => {
  await createNode(data); // Type-safe all the way
};

Type Generation Rules

1. Check OpenAPI First: packages/server/openapi-schema.yaml
2. Create in @journey/schema: All request/response types
3. Add Zod Schemas: For runtime validation
4. Export from Index: Make available to both server and client

🧩 Component Development

Component Decision Flow

Need Component?
    ↓
1. Check packages/components/ first ← **ALWAYS START HERE**
    ├── Exists & works? → Use it
    └── Doesn't exist or needs changes
        ↓
2. Is it reusable across features?
    ├── Yes → Create/extend in packages/components/
    └── No → Create in packages/ui/src/components/

Component Structure

packages/components/          # Reusable component library
    ├── src/
    │   ├── ui/              # shadcn/ui base components
    │   ├── custom/          # Custom reusable components
    │   └── index.ts         # Public exports

packages/ui/                 # Application-specific
    ├── src/components/
    │   ├── timeline/        # Timeline domain
    │   ├── search/          # Search domain
    │   ├── nodes/           # Node modals & forms
    │   └── user/            # User components
    └── pages/               # Route pages

Component Pattern (Figma-Based)

// packages/ui/src/components/timeline/NetworkInsightsSidePanel.tsx
import { ChevronDown, X } from 'lucide-react';
import { useState } from 'react';
// Import from @packages/components if reusable parts exist
import { Card, CardHeader } from '@packages/components';

interface NetworkInsightsSidePanelProps {
  data: GraphRAGSearchResponse | undefined;
  isLoading: boolean;
  matchCount: number;
  isOpen: boolean;
  onClose: () => void;
  onOpenModal: () => void;
}

export function NetworkInsightsSidePanel({
  data,
  isLoading,
  matchCount,
  isOpen,
  onClose,
  onOpenModal,
}: NetworkInsightsSidePanelProps) {
  const [isInsightsExpanded, setIsInsightsExpanded] = useState(true);

  if (!isOpen) return null;

  return (
    <div className="fixed bottom-0 right-0 top-[64px] z-50 w-[380px]">
      {/* Content matching Figma design specs */}
      <div className="flex items-start gap-[9px]">
        <div className="h-[92px] w-[4px] bg-[#5c9eeb] rounded-[2px]" />
        {/* ... */}
      </div>
    </div>
  );
}

Key Patterns:

• ALWAYS check packages/components/ first before creating
• Match Figma designs with exact spacing/colors
• Use lucide-react for icons
• Tailwind for styling with exact px values
• Loading and empty states built-in
• Prop-based show/hide (not CSS-only)

🎯 State Management Decision Tree

When to Use What?

graph TD
    A[State Needed] --> B{From Server?}
    B -->|Yes| C{Needs Caching?}
    B -->|No| D{Shared Across Components?}
    C -->|Yes| E[TanStack Query]
    C -->|No| F{One-time Fetch?}
    F -->|Yes| G[Direct API Call in useEffect]
    F -->|No| E
    D -->|Yes| H{Complex Logic?}
    D -->|No| I[Local useState]
    H -->|Yes| J[Zustand Store]
    H -->|No| K[React Context]

TanStack Query Patterns

// hooks/useNodeData.ts
export function useNodeData(nodeId: string) {
  return useQuery({
    queryKey: ['nodes', nodeId],
    queryFn: () => nodeApi.getNode(nodeId),
    staleTime: 5 * 60 * 1000, // 5 minutes
    enabled: !!nodeId, // Conditional fetching
    retry: 3,
    retryDelay: attemptIndex => Math.min(1000 * 2 ** attemptIndex, 30000)
  });
}

// Usage in component
function NodeDetail({ nodeId }) {
  const { data, isLoading, error } = useNodeData(nodeId);

  if (isLoading) return <Skeleton />;
  if (error) return <ErrorMessage />;
  return <NodeContent node={data} />;
}

Zustand Store Patterns

// stores/search-store.ts
import { create } from 'zustand';
import { devtools } from 'zustand/middleware';

interface SearchState {
  // UI state only (NOT server data)
  selectedProfileId: string | undefined;
  currentQuery: string;
  preloadedMatchData: GraphRAGSearchResponse | undefined;

  // Actions
  setSelectedProfile: (profileId: string | undefined) => void;
  setCurrentQuery: (query: string) => void;
  clearSelection: () => void;
  setPreloadedMatchData: (data: GraphRAGSearchResponse | undefined) => void;
  clearPreloadedData: () => void;
}

export const useSearchStore = create<SearchState>()(
  devtools(
    (set, get) => ({
      // Initial state
      selectedProfileId: undefined,
      currentQuery: '',
      preloadedMatchData: undefined,

      // Actions
      setSelectedProfile: (profileId) => {
        set({ selectedProfileId: profileId }, false, 'setSelectedProfile');
      },

      setCurrentQuery: (query) => {
        const currentQuery = get().currentQuery;

        // Clear selection when query changes
        if (query !== currentQuery) {
          set(
            {
              currentQuery: query,
              selectedProfileId: undefined,
            },
            false,
            'setCurrentQuery'
          );
        }
      },

      clearSelection: () => {
        set({ selectedProfileId: undefined }, false, 'clearSelection');
      },

      setPreloadedMatchData: (data) => {
        set({ preloadedMatchData: data }, false, 'setPreloadedMatchData');
      },

      clearPreloadedData: () => {
        set({ preloadedMatchData: undefined }, false, 'clearPreloadedData');
      },
    }),
    {
      name: 'search-store',
    }
  )
);

Key Patterns:

• Use devtools middleware for debugging
• Store name for DevTools identification
• Action names in set() for debugging
• Keep UI state separate from server state
• Clear related state on actions (e.g., clear selection on query change)

🔌 API Integration Patterns

Service Layer Structure

// services/node-api.ts
import { httpClient } from './http-client';
import {
  NodeResponse,
  CreateNodeRequestDTO,
  UpdateNodeRequestDTO,
  NodeResponseSchema, // Zod schema for validation
} from '@journey/schema';

class NodeAPI {
  async getNode(id: string): Promise<NodeResponse> {
    const response = await httpClient.get<NodeResponse>(`/api/v2/nodes/${id}`);
    // Validate response matches schema
    return NodeResponseSchema.parse(response);
  }

  async createNode(data: CreateNodeRequestDTO): Promise<NodeResponse> {
    const response = await httpClient.post<NodeResponse>('/api/v2/nodes', data);
    return NodeResponseSchema.parse(response);
  }

  async updateNode(
    id: string,
    data: UpdateNodeRequestDTO
  ): Promise<NodeResponse> {
    const response = await httpClient.patch<NodeResponse>(
      `/api/v2/nodes/${id}`,
      data
    );
    return NodeResponseSchema.parse(response);
  }
}

export const nodeApi = new NodeAPI();

HTTP Client Integration

// lib/queryClient.ts pattern
export async function apiRequest(
  method: string,
  url: string,
  data?: unknown
): Promise<Response> {
  const res = await fetch(url, {
    method,
    headers: data ? { 'Content-Type': 'application/json' } : {},
    body: data ? JSON.stringify(data) : undefined,
    credentials: 'include', // Always send cookies
  });

  if (!res.ok) {
    const text = (await res.text()) || res.statusText;
    throw new Error(`${res.status}: ${text}`);
  }
  return res;
}

// Default query function with 401 handling
export const getQueryFn: <T>(options: {
  on401: 'returnNull' | 'throw';
}) => QueryFunction<T> =
  ({ on401 }) =>
  async ({ queryKey }) => {
    const res = await fetch(queryKey.join('/'), {
      credentials: 'include',
    });

    if (on401 === 'returnNull' && res.status === 401) {
      return null;
    }

    if (!res.ok) {
      const text = (await res.text()) || res.statusText;
      throw new Error(`${res.status}: ${text}`);
    }
    return await res.json();
  };

Key Patterns:

• HTTP-only cookies (no localStorage tokens)
• credentials: "include" on all requests
• Global query function for consistency
• 401 handling at query client level

🧪 Testing Patterns

Testing Priority Order (CRITICAL)

1. Unit Tests First - Test logic in isolation (functions, hooks, components)
2. MSW Integration Tests - Test API interactions
3. E2E Tests Last - Only for critical user flows

ALWAYS write or update unit tests BEFORE MSW or integration tests.

Component Testing Setup with MSW

// components/NodeCard.test.tsx
import { render, screen, waitFor } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
import { vi } from 'vitest';

// MSW is set up globally in test/setup.ts
// Server starts before all tests, resets handlers between tests

// Test wrapper with providers
function TestWrapper({ children }: { children: React.ReactNode }) {
  const queryClient = new QueryClient({
    defaultOptions: {
      queries: { retry: false },
      mutations: { retry: false }
    }
  });

  return (
    <QueryClientProvider client={queryClient}>
      {children}
    </QueryClientProvider>
  );
}

describe('NodeCard', () => {
  it('should handle user interaction', async () => {
    const user = userEvent.setup();
    const onEdit = vi.fn();

    render(
      <TestWrapper>
        <NodeCard node={mockNode} onEdit={onEdit} />
      </TestWrapper>
    );

    await user.click(screen.getByRole('button', { name: /edit/i }));

    await waitFor(() => {
      expect(onEdit).toHaveBeenCalledWith(mockNode);
    });
  });
});

MSW Setup (Global)

// test/setup.ts
import { beforeAll, afterEach, afterAll } from 'vitest';
import { server } from '../mocks/server';

beforeAll(() => server.listen({ onUnhandledRequest: 'error' }));
afterEach(() => server.resetHandlers());
afterAll(() => server.close());

MSW Handler Patterns

// mocks/profile-handlers.ts
import { http, HttpResponse } from 'msw';

export const profileHandlers = [
  http.get('/api/v2/profiles/:id', ({ params }) => {
    const profile = mockProfiles.find((p) => p.id === params.id);

    if (!profile) {
      return HttpResponse.json({ error: 'Profile not found' }, { status: 404 });
    }

    return HttpResponse.json(profile);
  }),

  http.post('/api/v2/profiles', async ({ request }) => {
    const body = await request.json();
    const newProfile = { id: uuid(), ...body };

    return HttpResponse.json(newProfile, { status: 201 });
  }),
];

TanStack Query Testing

// Mock the API
vi.mock('../services/node-api', () => ({
  nodeApi: {
    getNode: vi.fn(),
    createNode: vi.fn(),
  },
}));

it('should fetch node data', async () => {
  const mockNode = { id: '1', title: 'Test' };
  vi.mocked(nodeApi.getNode).mockResolvedValue(mockNode);

  const { result } = renderHook(() => useNodeData('1'), {
    wrapper: TestWrapper,
  });

  await waitFor(() => {
    expect(result.current.data).toEqual(mockNode);
  });
});

Zustand Store Testing

// stores/__tests__/app-store.test.ts
import { renderHook, act } from '@testing-library/react';
import { useAppStore } from '../app-store';

describe('AppStore', () => {
  beforeEach(() => {
    // Reset store state
    useAppStore.setState({
      selectedNodeId: null,
      expandedNodes: new Set(),
    });
  });

  it('should select node', () => {
    const { result } = renderHook(() => useAppStore());

    act(() => {
      result.current.selectNode('node-1');
    });

    expect(result.current.selectedNodeId).toBe('node-1');
  });
});

📝 Form Handling Patterns

react-hook-form + Zod Integration

// components/forms/NodeForm.tsx
import { useForm } from 'react-hook-form';
import { zodResolver } from '@hookform/resolvers/zod';
import { CreateNodeRequestSchema, CreateNodeRequestDTO } from '@journey/schema';

export function NodeForm({ onSubmit }: { onSubmit: (data: CreateNodeRequestDTO) => void }) {
  const form = useForm<CreateNodeRequestDTO>({
    resolver: zodResolver(CreateNodeRequestSchema),
    defaultValues: {
      type: 'job',
      meta: {
        title: '',
        startDate: new Date().toISOString()
      }
    }
  });

  const handleSubmit = form.handleSubmit(async (data) => {
    try {
      await onSubmit(data);
      form.reset();
    } catch (error) {
      // Handle errors - could set form errors
      form.setError('root', {
        message: 'Failed to create node'
      });
    }
  });

  return (
    <form onSubmit={handleSubmit}>
      <input
        {...form.register('meta.title')}
        placeholder="Title"
      />
      {form.formState.errors.meta?.title && (
        <span>{form.formState.errors.meta.title.message}</span>
      )}

      <button type="submit" disabled={form.formState.isSubmitting}>
        {form.formState.isSubmitting ? 'Saving...' : 'Save'}
      </button>
    </form>
  );
}

Custom Form Components

// components/forms/FormField.tsx
import { Control, FieldPath, FieldValues } from 'react-hook-form';
import { FormControl, FormField, FormItem, FormLabel, FormMessage } from '@journey/components';

interface FormFieldProps<T extends FieldValues> {
  control: Control<T>;
  name: FieldPath<T>;
  label: string;
  placeholder?: string;
}

export function TextField<T extends FieldValues>({
  control,
  name,
  label,
  placeholder
}: FormFieldProps<T>) {
  return (
    <FormField
      control={control}
      name={name}
      render={({ field }) => (
        <FormItem>
          <FormLabel>{label}</FormLabel>
          <FormControl>
            <input
              {...field}
              placeholder={placeholder}
              className="w-full rounded-md border px-3 py-2"
            />
          </FormControl>
          <FormMessage />
        </FormItem>
      )}
    />
  );
}

🚀 Routing & Navigation (Wouter)

Protected Route Pattern

// components/auth/ProtectedRoute.tsx
import { Redirect } from 'wouter';
import { useAuthStore } from '@/stores/auth-store';

export function ProtectedRoute({ children }: { children: React.ReactNode }) {
  const { user, isLoading } = useAuthStore();

  if (isLoading) {
    return <LoadingSpinner />;
  }

  if (!user) {
    return <Redirect to="/signin" />;
  }

  return <>{children}</>;
}

// App.tsx route setup with wouter
import { Route, Switch } from 'wouter';

<Switch>
  <Route path="/signin" component={SignIn} />
  <Route path="/dashboard">
    <ProtectedRoute>
      <Dashboard />
    </ProtectedRoute>
  </Route>
  <Route path="/profile">
    <ProtectedRoute>
      <Profile />
    </ProtectedRoute>
  </Route>
</Switch>

Navigation State Management

// hooks/useNavigationState.ts
import { useLocation, useRoute } from 'wouter';

export function useNavigationState() {
  const [location, setLocation] = useLocation();
  const [previousPath, setPreviousPath] = useState<string | null>(null);

  useEffect(() => {
    setPreviousPath(location);
  }, [location]);

  const goBack = useCallback(() => {
    if (previousPath) {
      setLocation(previousPath);
    } else {
      setLocation('/');
    }
  }, [previousPath, setLocation]);

  return {
    currentPath: location,
    previousPath,
    goBack,
    navigate: setLocation,
  };
}

Error Boundaries

// components/ErrorBoundary.tsx
import { Component, ReactNode } from 'react';

interface Props {
  children: ReactNode;
  fallback?: (error: Error) => ReactNode;
}

interface State {
  hasError: boolean;
  error: Error | null;
}

export class ErrorBoundary extends Component<Props, State> {
  constructor(props: Props) {
    super(props);
    this.state = { hasError: false, error: null };
  }

  static getDerivedStateFromError(error: Error): State {
    return { hasError: true, error };
  }

  componentDidCatch(error: Error, errorInfo: any) {
    console.error('Error caught by boundary:', error, errorInfo);
    // Send to error tracking service
  }

  render() {
    if (this.state.hasError) {
      if (this.props.fallback) {
        return this.props.fallback(this.state.error!);
      }
      return <ErrorFallback error={this.state.error} />;
    }

    return this.props.children;
  }
}

// Usage in App.tsx
<ErrorBoundary fallback={(error) => <AppErrorPage error={error} />}>
  <App />
</ErrorBoundary>

🎨 Design System Foundation

Using @journey/components as Base

Design Token Usage

// All components use CSS variables from Tailwind config
// packages/components/tailwind.config.js defines:
// --primary, --secondary, --accent, --destructive, etc.

// Using in custom components
<div className="bg-primary text-primary-foreground">
  Uses CSS variable colors
</div>

Ensuring Consistency

1. Always check @journey/components first
2. Use CVA for variants - maintains consistency
3. Use cn() utility for conditional classes
4. Follow shadcn/ui patterns for new components

Extending Base Components

// Extend existing component with additional props
import { Button, ButtonProps } from '@journey/components';

interface LoadingButtonProps extends ButtonProps {
  isLoading?: boolean;
}

export function LoadingButton({
  isLoading,
  children,
  disabled,
  ...props
}: LoadingButtonProps) {
  return (
    <Button disabled={disabled || isLoading} {...props}>
      {isLoading && <Spinner className="mr-2" />}
      {children}
    </Button>
  );
}

🔄 Common Commands

# Navigate to package first
cd packages/ui

# Development
pnpm dev                    # Start dev server
pnpm build                  # Build for production
pnpm type-check            # Type checking

# Testing (IMPORTANT: Use smart testing)
pnpm test:changed           # ⚡️ FAST - Only test changed (unit only) - RECOMMENDED
pnpm test:unit              # Unit tests only (excludes e2e)
pnpm test                   # 🐢 SLOW - All tests including e2e

# Specific test file (FASTEST for focused work)
pnpm vitest run --no-coverage src/services/updates-api.test.ts
pnpm vitest --no-coverage src/services/updates-api.test.ts  # Watch mode

# From project root
pnpm test:changed           # Smart Nx testing - only affected packages
pnpm test:changed:base      # Compare to main branch

Testing Strategy:

• Development: pnpm test:changed (only tests what you changed)
• Focused work: pnpm vitest run --no-coverage [file]
• Watch mode: pnpm vitest --no-coverage [file] (auto-rerun)
• Pre-commit: pnpm test:unit (fast, no e2e)
• Pre-push: pnpm test (full suite)

📚 Learning & Skill Updates

How to Update This Skill

1. Identify New Pattern: During implementation
2. Verify Pattern: Used in multiple places
3. Document Location: Add to "Pattern References" table
4. Add Example: Include code example if complex
5. Update Skill: Edit .claude/skills/frontend-engineer/SKILL.md

What to Document

• ✅ New component patterns
• ✅ Complex TanStack Query patterns
• ✅ Zustand store patterns
• ✅ Form validation patterns
• ✅ Testing strategies
• ✅ API integration patterns
• ❌ One-off implementations
• ❌ Page-specific logic
• ❌ Temporary workarounds

Pattern Discovery Workflow

1. Check @journey/components for existing solutions
2. Review similar features in packages/ui
3. Check test files for patterns
4. Update skill with discoveries

🚀 Quick Reference

Essential Hooks

// Auth
useAuthStore(); // User, login, logout
useAuth(); // Auth utilities wrapper

// Data Fetching
useQuery(); // TanStack Query
useMutation(); // TanStack mutations
useInfiniteQuery(); // Pagination

// State
useHierarchyStore(); // Timeline state
useProfileReviewStore(); // Profile state

// Forms
useForm(); // react-hook-form
useFieldArray(); // Dynamic form fields

Component Checklist

• Check packages/components/ first ← CRITICAL
• Check packages/schema/src/api/ for types ← CRITICAL
• Type-safe with TypeScript
• Zod validation for forms
• Accessible (ARIA attributes)
• Responsive design
• Loading states
• Error handling
• Unit tests first, then MSW/integration ← CRITICAL

Performance Checklist

• Use React.memo for expensive components
• Optimize re-renders with useCallback/useMemo
• Lazy load routes with React.lazy
• Image optimization with proper formats
• Bundle splitting at route level

---

🎯 Critical Reminders

Before Any Development:

1. ✅ Check packages/components/ for reusable components
2. ✅ Check packages/schema/src/api/ for request/response types
3. ✅ Write unit tests BEFORE integration/MSW tests
4. ✅ Use pnpm test:changed during development
5. ✅ Use credentials: "include" for all API calls

Architecture Flow:

Component → TanStack Hook → API Service → fetch (credentials) → @schema/api types
              ↓
         Zustand (UI state only)

Remember: Maintain type safety across all layers. Always validate with Zod at boundaries. Check component library before creating new components.