arcana-react-developer-skill

name	arcana-react-developer-skill
description	React development guide based on Arcana React enterprise architecture. Provides comprehensive support for Clean Architecture, Offline-First design with 4-layer caching, React 19 hooks, MVVM Input/Output/Effect pattern, and enterprise security. Suitable for React project development, architecture design, code review, and debugging.
allowed-tools	["Read","Grep","Glob","Bash","Write","Edit"]

React Developer Skill

Professional React development skill based on Arcana React enterprise architecture.

---

⚡ Workflow — Always Start From the Reference Project

Every task starts by cloning the complete reference project — NEVER scaffold from scratch (no create-react-app / vite create):

git clone https://github.com/jrjohn/arcana-react.git [new-project-directory]

1. Clone the reference project (command above).
2. Build + test the UNTOUCHED clone first — npm install && npm run build && npm run test must be green before any modification (known-good baseline).
3. Follow 0. Project Setup to rename the project and strip demo code — KEEP the infrastructure: auth (guards/interceptors), 4-layer caching, offline/sync, security layers, DI/core (Context providers), router skeleton.
4. Add features by copying the nearest working feature, then adapting (see 🔁 Adding a feature) — the File-by-File Feature Recipe below is the completeness checklist.

🔁 Adding a feature = copy the nearest working feature (NOT from scratch)

When you add a new feature, do NOT re-create it from memory by walking the File-by-File Recipe on a blank slate. Copy the nearest already-working feature in the cloned reference, then adapt it.

1. Find the closest conformant feature already in the reference — e.g. the example users feature (user-list / user-detail / user-form) — it already has the full Model → Repository → Service → ViewModel (Input/Output/Effect) → Component → specs chain wired through DI.
2. Duplicate its ENTIRE file set (model, validator, service interface + impl, repository interface + impl, DTO, mapper, mock repository, provider binding + useXxxRepository hook, ViewModel hook, component, NavGraph methods, route, tests) 1:1, keeping every layer.
3. Rename + adapt to the new domain (types, routes, endpoints, DI bindings/providers).
4. Diff against the original to confirm nothing was dropped — same layer split, same ViewModel/service/repository boundary, same error model, same tests.

Why this is mandatory: the File-by-File Recipe is a checklist of what must exist, not a from-scratch build order. Re-deriving the pattern each time makes every step a chance to skip a layer (the ViewModel, the repository), wire a shortcut (component → data/API directly), or drop the tests — the "vibe-coding" deviations that pass local build + coverage but fail architecture review (e.g. arch-qube). Copying a known-good feature carries conformance in by construction; the recipe is then only your verification that nothing is missing.

Supporting files — load on demand

File	When to read
patterns.md	Detailed design patterns beyond the core examples in this file
patterns/mvvm-input-output.md	Deep-dive on the MVVM Input/Output/Effect ViewModel pattern
examples.md	Full working code examples for complete features
checklists/production-ready.md	Pre-release production & code review checklists
verification/commands.md	Complete catalog of verification bash commands

---

Quick Reference Card

New Screen Checklist:

1. Add route → router/routes.tsx (path + element)
2. Create Component with React.memo for optimization
3. Create useViewModel hook (Input/Output/Effect pattern)
4. Create template with Loading/Error/Empty states
5. Wire navigation callbacks in parent component
6. Verify mock data returns non-empty values

New Repository Checklist:

1. Interface → domain/repositories/xxx.repository.ts
2. Implementation → data/repositories/xxx.repository.impl.ts
3. Mock → data/repositories/mock/mock-xxx.repository.ts
4. Provider binding → core/providers/RepositoryProvider.tsx
5. Mock data (NEVER return [] or null!)
6. Verify ID consistency across repositories

Quick Diagnosis:

Symptom	Check Command
Blank screen	`grep -rn "[]\
Navigation crash	Compare routes.tsx paths vs component imports
Button does nothing	`grep -rn "onClick={undefined}\
Data not loading	`grep -rn "throw.*NotImplemented\

---

File-by-File Feature Recipe

Create files in this order when adding a new feature (example: project):

1. Model              -> domain/models/project.model.ts
2. Validator          -> domain/validators/project.validator.ts
3. Service Interface  -> domain/services/project.service.ts
4. Service Impl       -> domain/services/project.service.impl.ts
5. Repository Interface -> domain/repositories/project.repository.ts
6. Repository Impl    -> data/repositories/project.repository.impl.ts
7. DTO                -> data/remote/dtos/project.dto.ts
8. Mapper             -> data/remote/mappers/project.mapper.ts
9. Mock Repository    -> data/repositories/mock/mock-project.repository.ts
10. Provider Binding  -> core/providers/RepositoryProvider.tsx (+ useProjectRepository hook)
11. ViewModel Hook    -> presentation/pages/projects/useProjectViewModel.ts
12. Component         -> presentation/pages/projects/ProjectPage.tsx
13. NavGraph Methods  -> core/services/nav-graph.service.ts (toProjectList, toProjectDetail)
14. Route             -> router/routes.tsx (path + element)
15. Tests             -> useProjectViewModel.test.ts + service/repository tests

Step notes:

• 1-2: Model is a plain TypeScript interface; validator is a pure function module (no React imports).
• 3-6: Service depends on the repository INTERFACE (step 5), never the impl. Repository impl wraps the 4-layer cache + offline sync.
• 7-8: DTO mirrors the API payload exactly; mapper converts DTO <-> domain model. Never leak DTOs above the data layer.
• 9: Mock data must be realistic and non-empty (see Mock Data Rules — NEVER return []).
• 10: Register both impl and mock in RepositoryProvider.tsx (mock for DEV) and export a useProjectRepository() hook.
• 11: Hook follows the Input/Output/Effect pattern (discriminated-union Input, memoized Output, RxJS Subject for effects).
• 12: Wrap with React.memo, render Loading/Error/Empty/Content states, subscribe to effect$ in useEffect.
• 13-14: Every route added in routes.tsx MUST get a matching NavGraph method, and every navigation callback prop must be bound in the parent.
• 15: ViewModel hook tests first (90%+ target), then service (85%+) and repository (80%+) tests.

Verify after wiring: npm run type-check && npm run build && npm run test.

---

Rules Priority

CRITICAL (Must Fix Immediately)

Rule	Description	Verification
Zero-Empty Policy	Repository stubs NEVER return empty arrays	grep "\[\]" *.impl.ts
Route Wiring	ALL routes MUST have component imports	Count paths vs components
Callback Binding	ALL navigation callbacks MUST be bound	Check props drilling
ID Consistency	Cross-repository IDs must match	Check mock data IDs

IMPORTANT (Should Fix Before PR)

Rule	Description	Verification
UI States	Loading/Error/Empty for all screens	grep -L "isLoading" *.viewmodel.ts
Mock Data Quality	Realistic, varied values (not all same)	Review mock data arrays
Error Messages	User-friendly, not technical errors	Check error handling
React.memo	Performance-critical components memoized	Check component exports

RECOMMENDED (Nice to Have)

Rule	Description
Animations	Smooth route transitions with Framer Motion
Accessibility	ARIA labels for interactive elements
Dark Mode	Support system theme preference
PWA	Service worker for offline

---

Error Handling Pattern

AppError - Unified Error Model

// domain/models/app-error.ts
export type AppError =
  | { type: 'NETWORK_UNAVAILABLE' }
  | { type: 'TIMEOUT' }
  | { type: 'SERVER_ERROR'; statusCode: number }
  | { type: 'UNAUTHORIZED' }
  | { type: 'TOKEN_EXPIRED' }
  | { type: 'INVALID_CREDENTIALS' }
  | { type: 'NOT_FOUND' }
  | { type: 'VALIDATION_FAILED'; message: string }
  | { type: 'DATA_CORRUPTED' }
  | { type: 'UNKNOWN'; underlying: Error };

export function getErrorMessage(error: AppError): string {
  switch (error.type) {
    case 'NETWORK_UNAVAILABLE':
      return 'No internet connection. Please check your network.';
    case 'TIMEOUT':
      return 'Request timed out. Please try again.';
    case 'SERVER_ERROR':
      return `Server error (${error.statusCode}). Please try again later.`;
    case 'UNAUTHORIZED':
    case 'TOKEN_EXPIRED':
      return 'Session expired. Please login again.';
    case 'INVALID_CREDENTIALS':
      return 'Invalid email or password.';
    case 'NOT_FOUND':
      return 'The requested item was not found.';
    case 'VALIDATION_FAILED':
      return error.message;
    case 'DATA_CORRUPTED':
      return 'Data error. Please contact support.';
    case 'UNKNOWN':
      return 'An unexpected error occurred.';
  }
}

export function requiresReauth(error: AppError): boolean {
  return error.type === 'UNAUTHORIZED' || error.type === 'TOKEN_EXPIRED';
}

Error Handling Flow

┌─────────────────────────────────────────────────────────────────┐
│                        Error Flow                                │
├─────────────────────────────────────────────────────────────────┤
│  Repository Layer:                                               │
│    - Catch HTTP errors (Axios interceptors)                      │
│    - Map to AppError                                             │
│    - Throw AppError                                              │
├─────────────────────────────────────────────────────────────────┤
│  Service Layer:                                                  │
│    - Catch repository errors                                     │
│    - Add business context if needed                              │
│    - Re-throw as AppError                                        │
├─────────────────────────────────────────────────────────────────┤
│  ViewModel Hook:                                                 │
│    - Catch all errors                                            │
│    - Update error state with getErrorMessage()                   │
│    - Check requiresReauth() for auth redirect                    │
├─────────────────────────────────────────────────────────────────┤
│  Component Layer:                                                │
│    - Display error from output.error                             │
│    - Show retry button                                           │
│    - Handle auth redirect via useEffect                          │
└─────────────────────────────────────────────────────────────────┘

Error Handling by Layer

Axios Interceptor:

// core/api/axios-interceptor.ts
import axios, { AxiosError } from 'axios';
import { AppError } from '../../domain/models/app-error';

export const apiClient = axios.create({
  baseURL: import.meta.env.VITE_API_URL,
  timeout: 30000,
});

apiClient.interceptors.response.use(
  (response) => response,
  (error: AxiosError) => {
    let appError: AppError;

    if (!error.response) {
      appError = { type: 'NETWORK_UNAVAILABLE' };
    } else if (error.response.status === 401) {
      appError = { type: 'UNAUTHORIZED' };
    } else if (error.response.status === 404) {
      appError = { type: 'NOT_FOUND' };
    } else if (error.response.status >= 500) {
      appError = { type: 'SERVER_ERROR', statusCode: error.response.status };
    } else {
      appError = { type: 'UNKNOWN', underlying: error };
    }

    return Promise.reject(appError);
  }
);

ViewModel Hook:

const loadData = useCallback(async () => {
  setIsLoading(true);
  setError(null);

  try {
    const items = await repository.getItems();
    setItems(items);
  } catch (error) {
    const appError = error as AppError;
    setError(getErrorMessage(appError));
    if (requiresReauth(appError)) {
      emitEffect({ type: 'NAVIGATE_TO_LOGIN' });
    }
  } finally {
    setIsLoading(false);
  }
}, [repository]);

---

Test Coverage Targets

Coverage by Layer

Layer	Target	Focus Areas
ViewModel Hooks	90%+	All Input handlers, state transitions, effects
Service	85%+	Business logic, edge cases
Repository	80%+	Data mapping, error handling
Component	60%+	Template binding, user interactions

What to Test

ViewModel Hook Tests (Highest Priority):

describe('useFeatureViewModel', () => {
  // Test each Input type
  it('should load items on LOAD input', async () => { });
  it('should set error on LOAD failure', async () => { });
  it('should emit toast on REFRESH success', async () => { });
  it('should navigate on ITEM_CLICKED', () => { });

  // Test state transitions
  it('should set isLoading true then false', async () => { });

  // Test edge cases
  it('should show empty state when no items', async () => { });
});

Service Tests:

describe('UserService', () => {
  // Test business rules
  it('should validate email format', () => { });
  it('should calculate score correctly', () => { });
});

Repository Tests:

describe('UserRepository', () => {
  // Test data mapping
  it('should map DTO to domain model', async () => { });

  // Test offline behavior
  it('should return cached data when offline', async () => { });
});

Test Commands

# Run all tests with coverage
npm run test -- --coverage

# Run tests in watch mode
npm run test

# View coverage report
open coverage/index.html

---

Core Architecture Principles

Clean Architecture - Three Layers

┌─────────────────────────────────────────────────────┐
│                  Presentation Layer                  │
│    Components + Custom Hooks + Input/Output/Effect  │
├─────────────────────────────────────────────────────┤
│                    Domain Layer                      │
│          Business Logic + Services + Models         │
├─────────────────────────────────────────────────────┤
│                     Data Layer                       │
│   Offline-First Repository + IndexedDB + 4L Cache   │
└─────────────────────────────────────────────────────┘

Dependency Rules

• Unidirectional Dependencies: Presentation → Domain → Data
• Interface Segregation: Decouple layers through interfaces
• Dependency Inversion: Data layer implements Domain layer interfaces

Instructions

When handling React development tasks, follow these principles:

Quick Verification Commands

Use these commands to quickly check for common issues:

# 1. Check for unimplemented services (MUST be empty)
grep -rn "throw.*NotImplemented\|TODO.*implement" src/

# 2. Check for empty click handlers (MUST be empty)
grep -rn "onClick={undefined}\|onClick={() => {}}" src/

# 3. Check for missing route components (compare routes vs components)
echo "Routes defined:" && grep -c "path:" src/router/routes.tsx 2>/dev/null || echo 0
echo "Components imported:" && grep -c "element:" src/router/routes.tsx 2>/dev/null || echo 0

# 4. Check NavGraph has all navigation methods
grep -c "to\|navigate" src/core/services/nav-graph.service.ts 2>/dev/null || echo 0

# 5. Verify build compiles
npm run build

# 6. Check for navigation callbacks not wired (CRITICAL!)
echo "=== Navigation Props Defined ===" && \
grep -rh "onNavigate" src/presentation/ | grep -oE "onNavigate[A-Za-z]*" | sort -u
echo "=== Navigation Props Used ===" && \
grep -rh "onNavigate.*=" src/presentation/**/*.tsx 2>/dev/null | grep -oE "onNavigate[A-Za-z]*" | sort -u

# 7. Verify ALL routes have NavGraph navigation methods
echo "=== Routes Defined ===" && \
grep -rh "path:" src/router/routes.tsx | grep -oE "'[^']+'" | sort -u
echo "=== NavGraph Methods ===" && \
grep -rh "to[A-Z][a-zA-Z]*\(" src/core/services/nav-graph.service.ts | grep -oE "to[A-Z][a-zA-Z]*" | sort -u

# 8. Check Service→Repository wiring (CRITICAL!)
echo "=== Repository Methods Called in Services ===" && \
grep -roh "this\.[a-zA-Z]*Repository\.[a-zA-Z]*(" src/domain/services/*.ts | sort -u
echo "=== Repository Interface Methods ===" && \
grep -rh "[a-zA-Z]*\(" src/domain/repositories/*.repository.ts | grep -oE "[a-zA-Z]+\(" | sort -u

# 9. Check for empty array returns in Repository stubs (MUST FIX)
grep -rn "\[\]" src/data/repositories/*.repository.impl.ts

# 10. TypeScript type checking
npm run type-check

CRITICAL: All routes in routes.tsx MUST have corresponding component imports. Missing components cause runtime errors.

---

Mock Data Requirements for Repository Stubs

The Chart Data Problem

When implementing Repository stubs, NEVER return empty arrays for data that powers UI charts or visualizations. This causes:

• Charts that render but show nothing (blank Recharts/Chart.js canvas)
• Line charts that skip rendering (e.g., if (data.length < 2) return;)
• Empty state components even when data structure exists

Mock Data Rules

Rule 1: Array data for charts MUST have at least 7 items

// BAD - Chart will be blank
getCurrentWeekSummary(): Promise<WeeklySummary> {
    return Promise.resolve({
        dailyReports: []  // ← Chart has no data to render!
    });
}

// GOOD - Chart has data to display
getCurrentWeekSummary(): Promise<WeeklySummary> {
    const mockDailyReports = Array.from({ length: 7 }, (_, i) =>
        this.createMockDailyReport(
            [72, 78, 85, 80, 76, 88, 82][i],
            [390, 420, 450, 410, 380, 460, 435][i]
        )
    );
    return Promise.resolve({ dailyReports: mockDailyReports });
}

Rule 2: Use realistic, varied sample values

// BAD - Monotonous test data
const scores = Array(7).fill(80);

// GOOD - Realistic variation
const scores = [72, 78, 85, 80, 76, 88, 82];  // Shows trend

Rule 3: Data must match interface exactly

# Before creating mock data, ALWAYS verify the interface definition:
grep -A 20 "interface TherapyData" src/domain/models/*.ts

Rule 4: Create helper functions for complex mock data

// Create reusable mock factory
private createMockDailyReport(score: number, duration: number): DailySleepReport {
    return {
        id: `mock_${Date.now()}`,
        sleepScore: score,
        sleepDuration: { totalMinutes: duration, ... },
        // ... all required fields
    };
}

---

0. Project Setup - CRITICAL

IMPORTANT: This reference project has been validated with tested npm/React settings and library versions. NEVER reconfigure project structure or modify package.json / vite.config.ts, or it will cause compilation errors.

Step 1: Clone the reference project

git clone https://github.com/jrjohn/arcana-react.git [new-project-directory]
cd [new-project-directory]

Step 2: Reinitialize Git (remove original repo history)

rm -rf .git
git init
git add .
git commit -m "Initial commit from arcana-react template"

Step 3: Modify project name Only modify the following required items:

• name field in package.json
• <title> in index.html
• Update related settings in environment configuration files

Step 4: Clean up example code The cloned project contains example UI. Clean up and replace with new project screens:

Core architecture files to KEEP (do not delete):

• src/core/ - Common utilities (Guards, Interceptors, Services)
• src/shared/ - Shared components and hooks
• src/data/local/ - IndexedDB (Dexie) base configuration
• src/data/repositories/ - Repository base classes
• src/App.tsx - App entry point
• src/router/routes.tsx - Route configuration (modify routes)

Example files to REPLACE:

• src/presentation/ - Delete all example screens, create new project Components
• src/domain/models/ - Delete example Models, create new Domain Models
• src/data/remote/ - Modify API endpoints
• src/assets/ - Update resource files

Step 5: Install dependencies and verify build

npm install
npm run build

Prohibited Actions

• DO NOT create new React project from scratch (create-react-app/vite create)
• DO NOT modify version numbers in package.json
• DO NOT add or remove npm dependencies (unless explicitly required)
• DO NOT modify build settings in vite.config.ts
• DO NOT reconfigure Tailwind, React Router, or other library settings

Allowed Modifications

• Add business-related TypeScript code (following existing architecture)
• Add Components, Services, Custom Hooks
• Add Domain Models, Repository
• Modify resources in src/assets/
• Add route configurations

1. TDD & Spec-Driven Development Workflow - MANDATORY

CRITICAL: All development MUST follow this TDD workflow. Every Spec requirement must have corresponding tests BEFORE implementation.

ABSOLUTE RULE: TDD = Tests + Implementation. Writing tests without implementation is INCOMPLETE. Every test file MUST have corresponding production code that passes the tests.

┌─────────────────────────────────────────────────────────────────┐
│                    TDD Development Workflow                      │
├─────────────────────────────────────────────────────────────────┤
│  Step 1: Analyze Spec → Extract all SRS & SDD requirements      │
│  Step 2: Create Tests → Write tests for EACH Spec item          │
│  Step 3: Verify Coverage → Ensure 100% Spec coverage in tests   │
│  Step 4: Implement → Build features to pass tests  ⚠️ MANDATORY │
│  Step 5: Mock APIs → Use mock data for unfinished Cloud APIs    │
│  Step 6: Run All Tests → ALL tests must pass before completion  │
│  Step 7: Verify 100% → Tests written = Features implemented     │
└─────────────────────────────────────────────────────────────────┘

Placeholder Component Policy

Placeholder components are ONLY allowed as a temporary route during active development. They are FORBIDDEN as a final state.

// WRONG - Placeholder component left in production
{ path: 'training', element: <PlaceholderComponent /> } // FORBIDDEN!

// CORRECT - Real component implementation
{ path: 'training', element: <TrainingPage /> }

Placeholder Check Command:

# This command MUST return empty for production-ready code
grep -rn "PlaceholderComponent\|throw.*NotImplemented\|TODO.*implement\|Coming Soon" src/

2. Project Structure

src/
├── presentation/     # UI Layer
│   ├── components/   # Smart & Dumb Components
│   ├── layouts/      # Page Layouts
│   └── pages/        # Page Components
├── domain/           # Domain Layer
│   ├── models/       # Domain Models
│   ├── services/     # Business Services
│   └── repositories/ # Repository Interfaces
├── data/             # Data Layer
│   ├── repositories/ # Repository Implementations
│   ├── local/        # IndexedDB (Dexie)
│   └── remote/       # API Client (Axios)
├── core/             # Core utilities
│   ├── providers/    # Context Providers
│   ├── hooks/        # Shared hooks
│   └── services/     # Core services
├── shared/           # Shared components
├── router/           # React Router config
└── assets/

3. ViewModel Input/Output/Effect Pattern with Hooks

import { useState, useCallback, useMemo, useRef, useEffect } from 'react';
import { Subject } from 'rxjs';

// Input: Discriminated union defining all events
export type UserInput =
  | { type: 'UPDATE_NAME'; name: string }
  | { type: 'UPDATE_EMAIL'; email: string }
  | { type: 'SUBMIT' };

// Output: State container
export interface UserOutput {
  name: string;
  email: string;
  isLoading: boolean;
  error: string | null;
}

// Effect: One-time events
export type UserEffect =
  | { type: 'NAVIGATE_BACK' }
  | { type: 'SHOW_TOAST'; message: string };

export function useUserViewModel(userService: UserService) {
  // State
  const [name, setName] = useState('');
  const [email, setEmail] = useState('');
  const [isLoading, setIsLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);

  // Effect stream (using RxJS Subject)
  const effectRef = useRef(new Subject<UserEffect>());
  const effect$ = effectRef.current.asObservable();

  // Output (memoized)
  const output = useMemo<UserOutput>(() => ({
    name,
    email,
    isLoading,
    error,
  }), [name, email, isLoading, error]);

  // Input handler
  const onInput = useCallback(async (input: UserInput) => {
    switch (input.type) {
      case 'UPDATE_NAME':
        setName(input.name);
        break;
      case 'UPDATE_EMAIL':
        setEmail(input.email);
        break;
      case 'SUBMIT':
        await handleSubmit();
        break;
    }
  }, [name, email]);

  const handleSubmit = useCallback(async () => {
    setIsLoading(true);
    setError(null);

    try {
      await userService.updateUser({ name, email });
      effectRef.current.next({ type: 'NAVIGATE_BACK' });
    } catch (err) {
      setError(err instanceof Error ? err.message : 'Unknown error');
    } finally {
      setIsLoading(false);
    }
  }, [name, email, userService]);

  return { output, effect$, onInput };
}

4. Four-Layer Offline-First Caching

import Dexie from 'dexie';

interface CacheEntry<T> {
  value: T;
  timestamp: number;
}

export class CacheManager<T> {
  // L1: Memory cache (<1ms)
  private memoryCache = new Map<string, CacheEntry<T>>();

  // L2: LRU + TTL cache (~2ms)
  private lruCache = new Map<string, CacheEntry<T>>();
  private readonly maxLruSize = 100;
  private readonly ttlMs = 5 * 60 * 1000; // 5 minutes

  // L3: IndexedDB persistence (~10ms)
  private db: Dexie;

  constructor(private readonly tableName: string) {
    this.db = new Dexie('AppCache');
    this.db.version(1).stores({
      cache: 'key, value, timestamp',
    });
  }

  async get(key: string, loader: () => Promise<T>): Promise<T> {
    const now = Date.now();

    // Check L1: Memory cache
    const memEntry = this.memoryCache.get(key);
    if (memEntry && now - memEntry.timestamp < this.ttlMs) {
      return memEntry.value;
    }

    // Check L2: LRU cache
    const lruEntry = this.lruCache.get(key);
    if (lruEntry && now - lruEntry.timestamp < this.ttlMs) {
      this.memoryCache.set(key, lruEntry);
      return lruEntry.value;
    }

    // Check L3: IndexedDB
    const dbEntry = await this.db.table('cache').get(key);
    if (dbEntry && now - dbEntry.timestamp < this.ttlMs) {
      const entry = { value: dbEntry.value, timestamp: dbEntry.timestamp };
      this.memoryCache.set(key, entry);
      this.addToLru(key, entry);
      return dbEntry.value;
    }

    // L4: Load from remote
    const value = await loader();
    const entry = { value, timestamp: now };

    this.memoryCache.set(key, entry);
    this.addToLru(key, entry);
    await this.db.table('cache').put({ key, ...entry });

    return value;
  }

  private addToLru(key: string, entry: CacheEntry<T>): void {
    if (this.lruCache.size >= this.maxLruSize) {
      const oldestKey = this.lruCache.keys().next().value;
      if (oldestKey) this.lruCache.delete(oldestKey);
    }
    this.lruCache.set(key, entry);
  }
}

5. Component with React.memo

import React, { memo, useEffect } from 'react';
import { useUserViewModel, UserInput } from './useUserViewModel';
import { useNavGraph } from '../../core/hooks/useNavGraph';
import { useToast } from '../../shared/hooks/useToast';

interface UserFormProps {
  userService: UserService;
}

export const UserForm = memo<UserFormProps>(({ userService }) => {
  const { output, effect$, onInput } = useUserViewModel(userService);
  const navGraph = useNavGraph();
  const toast = useToast();

  // Handle effects
  useEffect(() => {
    const subscription = effect$.subscribe((effect) => {
      switch (effect.type) {
        case 'NAVIGATE_BACK':
          navGraph.back();
          break;
        case 'SHOW_TOAST':
          toast.show(effect.message);
          break;
      }
    });

    return () => subscription.unsubscribe();
  }, [effect$, navGraph, toast]);

  const handleNameChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    onInput({ type: 'UPDATE_NAME', name: e.target.value });
  };

  const handleEmailChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    onInput({ type: 'UPDATE_EMAIL', email: e.target.value });
  };

  const handleSubmit = (e: React.FormEvent) => {
    e.preventDefault();
    onInput({ type: 'SUBMIT' });
  };

  return (
    <form onSubmit={handleSubmit}>
      <div className="form-group">
        <label htmlFor="name">Name</label>
        <input
          id="name"
          type="text"
          value={output.name}
          onChange={handleNameChange}
        />
      </div>

      <div className="form-group">
        <label htmlFor="email">Email</label>
        <input
          id="email"
          type="email"
          value={output.email}
          onChange={handleEmailChange}
        />
      </div>

      {output.error && (
        <div className="error">{output.error}</div>
      )}

      <button type="submit" disabled={output.isLoading}>
        {output.isLoading ? 'Loading...' : 'Submit'}
      </button>
    </form>
  );
});

UserForm.displayName = 'UserForm';

6. Type-Safe Navigation (NavGraph Service)

// core/services/nav-graph.service.ts
import { useNavigate } from 'react-router-dom';
import { useCallback, useMemo } from 'react';

export function useNavGraph() {
  const navigate = useNavigate();

  return useMemo(() => ({
    toHome: () => navigate('/'),
    toUserList: () => navigate('/users'),
    toUserDetail: (userId: string) => navigate(`/users/${userId}`),
    toUserEdit: (userId: string) => navigate(`/users/${userId}/edit`),
    toProjectList: () => navigate('/projects'),
    toProjectDetail: (projectId: string) => navigate(`/projects/${projectId}`),
    toLogin: () => navigate('/login'),
    toForgotPassword: () => navigate('/forgot-password'),
    back: () => navigate(-1),
  }), [navigate]);
}

7. Context-Based Dependency Injection

// core/providers/RepositoryProvider.tsx
import React, { createContext, useContext, useMemo } from 'react';

interface Repositories {
  userRepository: IUserRepository;
  projectRepository: IProjectRepository;
  authRepository: IAuthRepository;
}

const RepositoryContext = createContext<Repositories | null>(null);

interface RepositoryProviderProps {
  children: React.ReactNode;
  useMock?: boolean;
}

export function RepositoryProvider({ children, useMock = false }: RepositoryProviderProps) {
  const repositories = useMemo<Repositories>(() => {
    if (useMock || import.meta.env.DEV) {
      return {
        userRepository: new MockUserRepository(),
        projectRepository: new MockProjectRepository(),
        authRepository: new MockAuthRepository(),
      };
    }
    return {
      userRepository: new UserRepositoryImpl(),
      projectRepository: new ProjectRepositoryImpl(),
      authRepository: new AuthRepositoryImpl(),
    };
  }, [useMock]);

  return (
    <RepositoryContext.Provider value={repositories}>
      {children}
    </RepositoryContext.Provider>
  );
}

export function useRepositories(): Repositories {
  const context = useContext(RepositoryContext);
  if (!context) {
    throw new Error('useRepositories must be used within RepositoryProvider');
  }
  return context;
}

// Individual repository hooks
export function useUserRepository(): IUserRepository {
  return useRepositories().userRepository;
}

export function useProjectRepository(): IProjectRepository {
  return useRepositories().projectRepository;
}

export function useAuthRepository(): IAuthRepository {
  return useRepositories().authRepository;
}

8. HTTP Interceptors with Axios

// core/api/axios-config.ts
import axios, { AxiosInstance, InternalAxiosRequestConfig, AxiosResponse, AxiosError } from 'axios';

export function createApiClient(getToken: () => string | null): AxiosInstance {
  const client = axios.create({
    baseURL: import.meta.env.VITE_API_URL,
    timeout: 30000,
  });

  // Request interceptor - Add auth token
  client.interceptors.request.use(
    (config: InternalAxiosRequestConfig) => {
      const token = getToken();
      if (token) {
        config.headers.Authorization = `Bearer ${token}`;
      }
      return config;
    },
    (error) => Promise.reject(error)
  );

  // Response interceptor - Handle errors
  client.interceptors.response.use(
    (response: AxiosResponse) => response,
    (error: AxiosError) => {
      if (error.response?.status === 401) {
        // Handle token expiry
        window.dispatchEvent(new CustomEvent('auth:logout'));
      }
      return Promise.reject(error);
    }
  );

  return client;
}

---

Navigation Wiring Verification Guide

The Navigation Wiring Blind Spot

React Components often have navigation callback props that need parent binding:

// SettingsPanel.tsx
interface SettingsPanelProps {
  onNavigateToAccountInfo?: () => void;  // Needs parent binding!
  onNavigateToChangePassword?: () => void;  // Needs parent binding!
  onNavigateToUserList?: () => void;  // Needs parent binding!
}

export const SettingsPanel: React.FC<SettingsPanelProps> = ({
  onNavigateToAccountInfo,
  onNavigateToChangePassword,
  onNavigateToUserList,
}) => {
  // If props are not provided, buttons do nothing!
  return (
    <button onClick={onNavigateToAccountInfo}>Account Info</button>
  );
};

Problem: If the parent Component doesn't pass these props, the buttons appear functional but do nothing when clicked!

Correct Wiring Example

// SettingsPage.tsx (Parent - correctly wired)
import { useNavGraph } from '../../core/hooks/useNavGraph';
import { SettingsPanel } from './SettingsPanel';

export const SettingsPage: React.FC = () => {
  const navGraph = useNavGraph();

  return (
    <SettingsPanel
      onNavigateToAccountInfo={navGraph.toAccountInfo}
      onNavigateToChangePassword={navGraph.toChangePassword}
      onNavigateToUserList={navGraph.toUserList}
    />
  );
};

// routes.tsx (routes exist)
export const routes: RouteObject[] = [
  { path: '/account-info', element: <AccountInfoPage /> },  // Route exists
  { path: '/change-password', element: <ChangePasswordPage /> },  // Route exists
  { path: '/user-list', element: <UserListPage /> },  // Route exists
];

---

Code Review Checklist

Required Items

• Follow Clean Architecture layering
• ViewModel uses Input/Output/Effect pattern with hooks
• Repository implements offline-first with IndexedDB
• Components use React.memo for optimization
• Type-safe navigation via useNavGraph hook
• No implicit any types (strict mode)
• ALL navigation callbacks are bound in parent components
• ALL routes have corresponding NavGraph methods
• ALL Service→Repository method calls exist in Repository interfaces
• ALL Repository interface methods have implementations

Performance Checks

• Use React.memo across presentational components
• Use useMemo/useCallback for expensive computations
• Implement virtual scrolling for large datasets (react-window)
• Use lazy loading and code splitting (React.lazy)

Security Checks

• Content Security Policy headers configured
• Input sanitization (DOMPurify for HTML)
• Axios interceptors for auth and error handling
• XSS/CSRF protection enabled
• No hardcoded API keys

---

Common Issues

Hook Dependency Issues

1. Include all dependencies in useEffect/useCallback/useMemo
2. Use ESLint react-hooks/exhaustive-deps rule
3. Avoid stale closures by proper dependency management

IndexedDB Issues

1. Handle version upgrades properly with Dexie
2. Use transactions for batch operations
3. Implement proper error handling

Build Optimization

1. Enable production mode
2. Configure tree shaking in Vite
3. Use lazy loading for route components

---

Spec Gap Prediction System

When Spec is incomplete, use these universal rules to predict and supplement missing UI/UX elements.

Screen Type → Required States (Universal)

Screen Type	Required States	Auto-Predict
List Screen	Loading, Error, Empty, Content	Virtual scroll, Search/Filter
Detail Screen	Loading, Error, Content	Back navigation, Edit action
Form Screen	Validation, Submit Loading, Success, Error	Input validation, Cancel action
Dashboard	Loading, Error, Content	Refresh, Section navigation
Settings	Content	Back navigation, Section headers
Auth Screen	Loading, Error, Success	Forgot password link, Terms link

Prediction Implementation Example

When implementing a List screen from Spec:

// Spec says: "Display user's items"
// Auto-predict required implementation:

export const ItemList: React.FC = () => {
  const { output, onInput } = useItemListViewModel();

  // 1. LOADING - Always needed for API/DB calls
  if (output.isLoading) {
    return (
      <div className="flex justify-center items-center h-64">
        <Spinner />
      </div>
    );
  }

  // 2. ERROR - Always needed for API/DB calls
  if (output.error) {
    return (
      <div className="text-center p-8">
        <p className="text-red-500">{output.error}</p>
        <button
          className="btn-primary mt-4"
          onClick={() => onInput({ type: 'RETRY' })}
        >
          Retry
        </button>
      </div>
    );
  }

  // 3. EMPTY - Always needed for list screens
  if (output.items.length === 0) {
    return (
      <div className="text-center p-8">
        <h3 className="text-xl font-semibold">No Items</h3>
        <p className="text-gray-500">Add your first item to get started</p>
        <button
          className="btn-primary mt-4"
          onClick={() => onInput({ type: 'ADD_CLICKED' })}
        >
          Add Item
        </button>
      </div>
    );
  }

  // 4. CONTENT - The actual list
  return (
    <ul className="divide-y">
      {output.items.map((item) => (
        <li
          key={item.id}
          className="p-4 hover:bg-gray-50 cursor-pointer"
          onClick={() => onInput({ type: 'ITEM_CLICKED', id: item.id })}
        >
          {item.name}
        </li>
      ))}
    </ul>
  );
};

---

Tech Stack Reference

Technology	Recommended Version
React	19.1+
TypeScript	5.8+
Vite	6.3+
React Router	7.0+
Axios	Latest
RxJS	7.8+
Tailwind CSS	4.0+
Dexie	4.0+
react-i18next	Latest
Vitest	Latest
React Testing Library	Latest