Initial commit

2025-11-30 08:42:54 +08:00
commit 8aa65dc62a
10 changed files with 2457 additions and 0 deletions
--- a/skills/kaizen/SKILL.md
+++ b/skills/kaizen/SKILL.md
@@ -0,0 +1,733 @@
+---
+name: kaizen
+description: Use when Code implementation and refactoring, architecturing or designing systems, process and workflow improvements, error handling and validation. Provide tehniquest to avoid over-engineering and apply iterative improvements.
+---
+
+# Kaizen: Continuous Improvement
+
+Apply continuous improvement mindset - suggest small iterative improvements, error-proof designs, follow established patterns, avoid over-engineering; automatically applied to guide quality and simplicity
+
+## Overview
+
+Small improvements, continuously. Error-proof by design. Follow what works. Build only what's needed.
+
+**Core principle:** Many small improvements beat one big change. Prevent errors at design time, not with fixes.
+
+## When to Use
+
+**Always applied for:**
+
+- Code implementation and refactoring
+- Architecture and design decisions
+- Process and workflow improvements
+- Error handling and validation
+
+**Philosophy:** Quality through incremental progress and prevention, not perfection through massive effort.
+
+## The Four Pillars
+
+### 1. Continuous Improvement (Kaizen)
+
+Small, frequent improvements compound into major gains.
+
+#### Principles
+
+**Incremental over revolutionary:**
+
+- Make smallest viable change that improves quality
+- One improvement at a time
+- Verify each change before next
+- Build momentum through small wins
+
+**Always leave code better:**
+
+- Fix small issues as you encounter them
+- Refactor while you work (within scope)
+- Update outdated comments
+- Remove dead code when you see it
+
+**Iterative refinement:**
+
+- First version: make it work
+- Second pass: make it clear
+- Third pass: make it efficient
+- Don't try all three at once
+
+<Good>
+```typescript
+// Iteration 1: Make it work
+const calculateTotal = (items: Item[]) => {
+  let total = 0;
+  for (let i = 0; i < items.length; i++) {
+    total += items[i].price * items[i].quantity;
+  }
+  return total;
+};
+
+// Iteration 2: Make it clear (refactor)
+const calculateTotal = (items: Item[]): number => {
+  return items.reduce((total, item) => {
+    return total + (item.price * item.quantity);
+  }, 0);
+};
+
+// Iteration 3: Make it robust (add validation)
+const calculateTotal = (items: Item[]): number => {
+  if (!items?.length) return 0;
+  
+  return items.reduce((total, item) => {
+    if (item.price < 0 || item.quantity < 0) {
+      throw new Error('Price and quantity must be non-negative');
+    }
+    return total + (item.price * item.quantity);
+  }, 0);
+};
+
+```
+Each step is complete, tested, and working
+</Good>
+
+<Bad>
+```typescript
+// Trying to do everything at once
+const calculateTotal = (items: Item[]): number => {
+  // Validate, optimize, add features, handle edge cases all together
+  if (!items?.length) return 0;
+  const validItems = items.filter(item => {
+    if (item.price < 0) throw new Error('Negative price');
+    if (item.quantity < 0) throw new Error('Negative quantity');
+    return item.quantity > 0; // Also filtering zero quantities
+  });
+  // Plus caching, plus logging, plus currency conversion...
+  return validItems.reduce(...); // Too many concerns at once
+};
+```
+
+Overwhelming, error-prone, hard to verify
+</Bad>
+
+#### In Practice
+
+**When implementing features:**
+
+1. Start with simplest version that works
+2. Add one improvement (error handling, validation, etc.)
+3. Test and verify
+4. Repeat if time permits
+5. Don't try to make it perfect immediately
+
+**When refactoring:**
+
+- Fix one smell at a time
+- Commit after each improvement
+- Keep tests passing throughout
+- Stop when "good enough" (diminishing returns)
+
+**When reviewing code:**
+
+- Suggest incremental improvements (not rewrites)
+- Prioritize: critical → important → nice-to-have
+- Focus on highest-impact changes first
+- Accept "better than before" even if not perfect
+
+### 2. Poka-Yoke (Error Proofing)
+
+Design systems that prevent errors at compile/design time, not runtime.
+
+#### Principles
+
+**Make errors impossible:**
+
+- Type system catches mistakes
+- Compiler enforces contracts
+- Invalid states unrepresentable
+- Errors caught early (left of production)
+
+**Design for safety:**
+
+- Fail fast and loudly
+- Provide helpful error messages
+- Make correct path obvious
+- Make incorrect path difficult
+
+**Defense in layers:**
+
+1. Type system (compile time)
+2. Validation (runtime, early)
+3. Guards (preconditions)
+4. Error boundaries (graceful degradation)
+
+#### Type System Error Proofing
+
+<Good>
+```typescript
+// Error: string status can be any value
+type OrderBad = {
+  status: string; // Can be "pending", "PENDING", "pnding", anything!
+  total: number;
+};
+
+// Good: Only valid states possible
+type OrderStatus = 'pending' | 'processing' | 'shipped' | 'delivered';
+type Order = {
+  status: OrderStatus;
+  total: number;
+};
+
+// Better: States with associated data
+type Order =
+  | { status: 'pending'; createdAt: Date }
+  | { status: 'processing'; startedAt: Date; estimatedCompletion: Date }
+  | { status: 'shipped'; trackingNumber: string; shippedAt: Date }
+  | { status: 'delivered'; deliveredAt: Date; signature: string };
+
+// Now impossible to have shipped without trackingNumber
+
+```
+Type system prevents entire classes of errors
+</Good>
+
+<Good>
+```typescript
+// Make invalid states unrepresentable
+type NonEmptyArray<T> = [T, ...T[]];
+
+const firstItem = <T>(items: NonEmptyArray<T>): T => {
+  return items[0]; // Always safe, never undefined!
+};
+
+// Caller must prove array is non-empty
+const items: number[] = [1, 2, 3];
+if (items.length > 0) {
+  firstItem(items as NonEmptyArray<number>); // Safe
+}
+```
+
+Function signature guarantees safety
+</Good>
+
+#### Validation Error Proofing
+
+<Good>
+```typescript
+// Error: Validation after use
+const processPayment = (amount: number) => {
+  const fee = amount * 0.03; // Used before validation!
+  if (amount <= 0) throw new Error('Invalid amount');
+  // ...
+};
+
+// Good: Validate immediately
+const processPayment = (amount: number) => {
+  if (amount <= 0) {
+    throw new Error('Payment amount must be positive');
+  }
+  if (amount > 10000) {
+    throw new Error('Payment exceeds maximum allowed');
+  }
+  
+  const fee = amount * 0.03;
+  // ... now safe to use
+};
+
+// Better: Validation at boundary with branded type
+type PositiveNumber = number & { readonly __brand: 'PositiveNumber' };
+
+const validatePositive = (n: number): PositiveNumber => {
+  if (n <= 0) throw new Error('Must be positive');
+  return n as PositiveNumber;
+};
+
+const processPayment = (amount: PositiveNumber) => {
+  // amount is guaranteed positive, no need to check
+  const fee = amount * 0.03;
+};
+
+// Validate at system boundary
+const handlePaymentRequest = (req: Request) => {
+  const amount = validatePositive(req.body.amount); // Validate once
+  processPayment(amount); // Use everywhere safely
+};
+
+```
+Validate once at boundary, safe everywhere else
+</Good>
+
+#### Guards and Preconditions
+
+<Good>
+```typescript
+// Early returns prevent deeply nested code
+const processUser = (user: User | null) => {
+  if (!user) {
+    logger.error('User not found');
+    return;
+  }
+  
+  if (!user.email) {
+    logger.error('User email missing');
+    return;
+  }
+  
+  if (!user.isActive) {
+    logger.info('User inactive, skipping');
+    return;
+  }
+  
+  // Main logic here, guaranteed user is valid and active
+  sendEmail(user.email, 'Welcome!');
+};
+```
+
+Guards make assumptions explicit and enforced
+</Good>
+
+#### Configuration Error Proofing
+
+<Good>
+```typescript
+// Error: Optional config with unsafe defaults
+type ConfigBad = {
+  apiKey?: string;
+  timeout?: number;
+};
+
+const client = new APIClient({ timeout: 5000 }); // apiKey missing!
+
+// Good: Required config, fails early
+type Config = {
+  apiKey: string;
+  timeout: number;
+};
+
+const loadConfig = (): Config => {
+  const apiKey = process.env.API_KEY;
+  if (!apiKey) {
+    throw new Error('API_KEY environment variable required');
+  }
+  
+  return {
+    apiKey,
+    timeout: 5000,
+  };
+};
+
+// App fails at startup if config invalid, not during request
+const config = loadConfig();
+const client = new APIClient(config);
+
+```
+Fail at startup, not in production
+</Good>
+
+#### In Practice
+
+**When designing APIs:**
+- Use types to constrain inputs
+- Make invalid states unrepresentable
+- Return Result<T, E> instead of throwing
+- Document preconditions in types
+
+**When handling errors:**
+- Validate at system boundaries
+- Use guards for preconditions
+- Fail fast with clear messages
+- Log context for debugging
+
+**When configuring:**
+- Required over optional with defaults
+- Validate all config at startup
+- Fail deployment if config invalid
+- Don't allow partial configurations
+
+### 3. Standardized Work
+
+Follow established patterns. Document what works. Make good practices easy to follow.
+
+#### Principles
+
+**Consistency over cleverness:**
+- Follow existing codebase patterns
+- Don't reinvent solved problems
+- New pattern only if significantly better
+- Team agreement on new patterns
+
+**Documentation lives with code:**
+- README for setup and architecture
+- CLAUDE.md for AI coding conventions
+- Comments for "why", not "what"
+- Examples for complex patterns
+
+**Automate standards:**
+- Linters enforce style
+- Type checks enforce contracts
+- Tests verify behavior
+- CI/CD enforces quality gates
+
+#### Following Patterns
+
+<Good>
+```typescript
+// Existing codebase pattern for API clients
+class UserAPIClient {
+  async getUser(id: string): Promise<User> {
+    return this.fetch(`/users/${id}`);
+  }
+}
+
+// New code follows the same pattern
+class OrderAPIClient {
+  async getOrder(id: string): Promise<Order> {
+    return this.fetch(`/orders/${id}`);
+  }
+}
+```
+
+Consistency makes codebase predictable
+</Good>
+
+<Bad>
+```typescript
+// Existing pattern uses classes
+class UserAPIClient { /* ... */ }
+
+// New code introduces different pattern without discussion
+const getOrder = async (id: string): Promise<Order> => {
+  // Breaking consistency "because I prefer functions"
+};
+
+```
+Inconsistency creates confusion
+</Bad>
+
+#### Error Handling Patterns
+
+<Good>
+```typescript
+// Project standard: Result type for recoverable errors
+type Result<T, E> = { ok: true; value: T } | { ok: false; error: E };
+
+// All services follow this pattern
+const fetchUser = async (id: string): Promise<Result<User, Error>> => {
+  try {
+    const user = await db.users.findById(id);
+    if (!user) {
+      return { ok: false, error: new Error('User not found') };
+    }
+    return { ok: true, value: user };
+  } catch (err) {
+    return { ok: false, error: err as Error };
+  }
+};
+
+// Callers use consistent pattern
+const result = await fetchUser('123');
+if (!result.ok) {
+  logger.error('Failed to fetch user', result.error);
+  return;
+}
+const user = result.value; // Type-safe!
+```
+
+Standard pattern across codebase
+</Good>
+
+#### Documentation Standards
+
+<Good>
+```typescript
+/**
+ * Retries an async operation with exponential backoff.
+ *
+ * Why: Network requests fail temporarily; retrying improves reliability
+ * When to use: External API calls, database operations
+ * When not to use: User input validation, internal function calls
+ *
+ * @example
+ * const result = await retry(
+ *   () => fetch('https://api.example.com/data'),
+ *   { maxAttempts: 3, baseDelay: 1000 }
+ * );
+ */
+const retry = async <T>(
+  operation: () => Promise<T>,
+  options: RetryOptions
+): Promise<T> => {
+  // Implementation...
+};
+```
+Documents why, when, and how
+</Good>
+
+#### In Practice
+
+**Before adding new patterns:**
+
+- Search codebase for similar problems solved
+- Check CLAUDE.md for project conventions
+- Discuss with team if breaking from pattern
+- Update docs when introducing new pattern
+
+**When writing code:**
+
+- Match existing file structure
+- Use same naming conventions
+- Follow same error handling approach
+- Import from same locations
+
+**When reviewing:**
+
+- Check consistency with existing code
+- Point to examples in codebase
+- Suggest aligning with standards
+- Update CLAUDE.md if new standard emerges
+
+### 4. Just-In-Time (JIT)
+
+Build what's needed now. No more, no less. Avoid premature optimization and over-engineering.
+
+#### Principles
+
+**YAGNI (You Aren't Gonna Need It):**
+
+- Implement only current requirements
+- No "just in case" features
+- No "we might need this later" code
+- Delete speculation
+
+**Simplest thing that works:**
+
+- Start with straightforward solution
+- Add complexity only when needed
+- Refactor when requirements change
+- Don't anticipate future needs
+
+**Optimize when measured:**
+
+- No premature optimization
+- Profile before optimizing
+- Measure impact of changes
+- Accept "good enough" performance
+
+#### YAGNI in Action
+
+<Good>
+```typescript
+// Current requirement: Log errors to console
+const logError = (error: Error) => {
+  console.error(error.message);
+};
+```
+Simple, meets current need
+</Good>
+
+<Bad>
+```typescript
+// Over-engineered for "future needs"
+interface LogTransport {
+  write(level: LogLevel, message: string, meta?: LogMetadata): Promise<void>;
+}
+
+class ConsoleTransport implements LogTransport { /*... */ }
+class FileTransport implements LogTransport { /* ... */ }
+class RemoteTransport implements LogTransport { /* ...*/ }
+
+class Logger {
+  private transports: LogTransport[] = [];
+  private queue: LogEntry[] = [];
+  private rateLimiter: RateLimiter;
+  private formatter: LogFormatter;
+  
+  // 200 lines of code for "maybe we'll need it"
+}
+
+const logError = (error: Error) => {
+  Logger.getInstance().log('error', error.message);
+};
+
+```
+Building for imaginary future requirements
+</Bad>
+
+**When to add complexity:**
+- Current requirement demands it
+- Pain points identified through use
+- Measured performance issues
+- Multiple use cases emerged
+
+<Good>
+```typescript
+// Start simple
+const formatCurrency = (amount: number): string => {
+  return `$${amount.toFixed(2)}`;
+};
+
+// Requirement evolves: support multiple currencies
+const formatCurrency = (amount: number, currency: string): string => {
+  const symbols = { USD: '$', EUR: '€', GBP: '£' };
+  return `${symbols[currency]}${amount.toFixed(2)}`;
+};
+
+// Requirement evolves: support localization
+const formatCurrency = (amount: number, locale: string): string => {
+  return new Intl.NumberFormat(locale, {
+    style: 'currency',
+    currency: locale === 'en-US' ? 'USD' : 'EUR',
+  }).format(amount);
+};
+```
+
+Complexity added only when needed
+</Good>
+
+#### Premature Abstraction
+
+<Bad>
+```typescript
+// One use case, but building generic framework
+abstract class BaseCRUDService<T> {
+  abstract getAll(): Promise<T[]>;
+  abstract getById(id: string): Promise<T>;
+  abstract create(data: Partial<T>): Promise<T>;
+  abstract update(id: string, data: Partial<T>): Promise<T>;
+  abstract delete(id: string): Promise<void>;
+}
+
+class GenericRepository<T> { /*300 lines */ }
+class QueryBuilder<T> { /* 200 lines*/ }
+// ... building entire ORM for single table
+
+```
+Massive abstraction for uncertain future
+</Bad>
+
+<Good>
+```typescript
+// Simple functions for current needs
+const getUsers = async (): Promise<User[]> => {
+  return db.query('SELECT * FROM users');
+};
+
+const getUserById = async (id: string): Promise<User | null> => {
+  return db.query('SELECT * FROM users WHERE id = $1', [id]);
+};
+
+// When pattern emerges across multiple entities, then abstract
+```
+
+Abstract only when pattern proven across 3+ cases
+</Good>
+
+#### Performance Optimization
+
+<Good>
+```typescript
+// Current: Simple approach
+const filterActiveUsers = (users: User[]): User[] => {
+  return users.filter(user => user.isActive);
+};
+
+// Benchmark shows: 50ms for 1000 users (acceptable)
+// ✓ Ship it, no optimization needed
+
+// Later: After profiling shows this is bottleneck
+// Then optimize with indexed lookup or caching
+
+```
+Optimize based on measurement, not assumptions
+</Good>
+
+<Bad>
+```typescript
+// Premature optimization
+const filterActiveUsers = (users: User[]): User[] => {
+  // "This might be slow, so let's cache and index"
+  const cache = new WeakMap();
+  const indexed = buildBTreeIndex(users, 'isActive');
+  // 100 lines of optimization code
+  // Adds complexity, harder to maintain
+  // No evidence it was needed
+};
+```
+
+Complex solution for unmeasured problem
+</Bad>
+
+#### In Practice
+
+**When implementing:**
+
+- Solve the immediate problem
+- Use straightforward approach
+- Resist "what if" thinking
+- Delete speculative code
+
+**When optimizing:**
+
+- Profile first, optimize second
+- Measure before and after
+- Document why optimization needed
+- Keep simple version in tests
+
+**When abstracting:**
+
+- Wait for 3+ similar cases (Rule of Three)
+- Make abstraction as simple as possible
+- Prefer duplication over wrong abstraction
+- Refactor when pattern clear
+
+## Integration with Commands
+
+The Kaizen skill guides how you work. The commands provide structured analysis:
+
+- **`/why`**: Root cause analysis (5 Whys)
+- **`/cause-and-effect`**: Multi-factor analysis (Fishbone)
+- **`/plan-do-check-act`**: Iterative improvement cycles
+- **`/analyse-problem`**: Comprehensive documentation (A3)
+- **`/analyse`**: Smart method selection (Gemba/VSM/Muda)
+
+Use commands for structured problem-solving. Apply skill for day-to-day development.
+
+## Red Flags
+
+**Violating Continuous Improvement:**
+
+- "I'll refactor it later" (never happens)
+- Leaving code worse than you found it
+- Big bang rewrites instead of incremental
+
+**Violating Poka-Yoke:**
+
+- "Users should just be careful"
+- Validation after use instead of before
+- Optional config with no validation
+
+**Violating Standardized Work:**
+
+- "I prefer to do it my way"
+- Not checking existing patterns
+- Ignoring project conventions
+
+**Violating Just-In-Time:**
+
+- "We might need this someday"
+- Building frameworks before using them
+- Optimizing without measuring
+
+## Remember
+
+**Kaizen is about:**
+
+- Small improvements continuously
+- Preventing errors by design
+- Following proven patterns
+- Building only what's needed
+
+**Not about:**
+
+- Perfection on first try
+- Massive refactoring projects
+- Clever abstractions
+- Premature optimization
+
+**Mindset:** Good enough today, better tomorrow. Repeat.