Clean Code

---
name: clean-code
description: "Use when auditing, pen-testing, hardening, and verifying code against clean code vulnerabilities, injection vectors, and auth flaws."
version: 6.0.0
last-updated: 2026-09-29
skills:
  - codebase-design
  - code-review-checklist
  - tdd-workflow
tools: Read, Grep, Glob, Bash, Edit, Write
scripts-binding:
  - .agent/scripts/lint_runner.js
  - .agent/scripts/verify_all.js
---

# Clean Code — The Art of Readable Software

## Mandatory Pre-Flight Context Inspection
Before reading, generating, or refactoring code in the `clean-code` domain, inspect these 5 critical parameters:
1. **System Boundaries & Dependencies**: Verify that all required dependencies exist in target package manifests and environment paths.
2. **Runtime Context & Platform Invariants**: Confirm target platform constraints (Node.js, Browser, Mobile OS, Edge runtime) before applying APIs.
3. **Execution Guardrails**: Identify potential side-effects, state mutations, and unhandled asynchronous exceptions.
4. **Validation & Type Contracts**: Validate input data schemas and strict type constraints across all module interfaces.
5. **Observability & Proof of Execution**: Ensure execution produces tangible verification signals (terminal output, tests, metrics).


## Activation Boundaries
- **Activate when:** Use when auditing, pen-testing, hardening, and verifying code against clean code vulnerabilities, injection vectors, and auth flaws.
- **DO NOT activate when:** The task falls outside the `clean-code` domain or is managed by a different dedicated specialist agent.


## 🔁 Multi-Pass Execution Protocol

| Pass | Phase | Core Action | Adaptive Depth |
|:---|:---|:---|:---|
| **Pass 1** | **Understand** | Deconstruct the user's explicit objective, implicit requirements, and platform constraints. | Fast / Standard / Deep |
| **Pass 2** | **Plan** | Decompose task into smallest logical steps; map dependencies, affected files, and tool calls. | Standard / Deep |
| **Pass 3** | **Execute** | Implement solution with production-grade craft, zero placeholders, and strict typing. | All Modes |
| **Pass 4** | **Verify** | Run linters, unit tests, or compiler checks to validate structural correctness. | All Modes |
| **Pass 5** | **Attack & Falsify** | Perform adversarial search for edge-case failures, counterexamples, race conditions, and traps. | Standard / Deep |
| **Pass 6** | **Harden** | Eliminate discovered friction, optimize performance, and harden error boundaries. | Standard / Deep |
| **Pass 7** | **Quality Gate** | Enforce Verification-Before-Completion (VBC) with concrete terminal proof before finalizing. | All Modes |


---

## 🛠️ Technical Architecture & Reference Recipes

## 2026 Code Performance & Logic Invariants

1. **Fail-Fast Early Returns**: Flatten nested conditionals (`if ... else if ... else`). Return or throw immediately on validation failure.
2. **O(1) Data Structures**: Replace repeated `array.find()` or `array.includes()` in loops with `Set.has()` or `Map.get()`.
3. **Cyclomatic Complexity Cap**: No single function may exceed cyclomatic complexity > 10. Split multi-branch operations into dedicated strategy handlers.
4. **Pure Core, Imperative Shell**: Keep business calculations pure and deterministic; push network I/O, file access, and mutation to the boundaries.
5. **Typed Error Hierarchy**: Never throw raw strings or generic `Error`. Throw domain-specific error classes containing structured metadata (`code`, `retryable`, `context`).

## Hallucination Traps (Read First)

- ❌ Over-abstracting code that is used in only one place -> ✅ Don't DRY single-use code; premature abstraction is worse than duplication
- ❌ Adding comments that restate what the code does -> ✅ Comments explain WHY, not WHAT; the code explains what
- ❌ Creating utility functions for trivial one-liners -> ✅ Inline is clearer when the operation is self-documenting
- ❌ Using `array.find()` inside an `array.filter()` loop (O(N²)) -> ✅ Index into a `Map` first (O(N))

---

## Naming

### Variables & Functions

```typescript
// ❌ BAD: Cryptic, abbreviated, meaningless
const d = new Date();
const u = getU();
const flag = true;
function proc(x: number): number {
  return x * 1.08;
}

// ✅ GOOD: Self-documenting, reveals intent
const registrationDate = new Date();
const currentUser = getCurrentUser();
const isEligibleForDiscount = true;
function addSalesTax(price: number): number {
  return price * 1.08;
}
```

### Booleans

```typescript
// ❌ BAD                    ✅ GOOD
const active = true;
const isActive = true;
const admin = false;
const hasAdminRole = false;
const loading = true;
const isLoading = true;
const open = false;
const isModalOpen = false;
const valid = true;
const canSubmit = true;

// Boolean function names start with is/has/can/should
function isExpired(token: Token): boolean {}
function hasPermission(user: User, action: string): boolean {}
function canRetry(attempt: number): boolean {}
function shouldNotify(event: Event): boolean {}
```

### Constants & Enums

```typescript
// ❌ BAD: Magic numbers and strings
if (user.role === 3) { ... }
if (retries > 5) { ... }
const delay = 86400000;

// ✅ GOOD: Named constants with meaning
const MAX_RETRY_ATTEMPTS = 5;
const ONE_DAY_MS = 24 * 60 * 60 * 1000;

enum UserRole {
  VIEWER = "viewer",
  EDITOR = "editor",
  ADMIN = "admin",
}

if (user.role === UserRole.ADMIN) { ... }
if (retries > MAX_RETRY_ATTEMPTS) { ... }
```

---

## Function Design

### Small, Single-Purpose Functions

```typescript
// ❌ BAD: Does 5 things in one function
async function processOrder(order: Order) {
  // validate
  if (!order.items.length) throw new Error('Empty');
  if (order.total < 0) throw new Error('Negative');
  // calculate
  const subtotal = order.items.reduce((sum, i) => sum + i.price * i.qty, 0);
  const tax = subtotal * 0.08;
  const total = subtotal + tax;
  // save
  await db.orders.insert({ ...order, total });
  // notify
  await emailService.send(order.userId, 'Order placed');
  // log
  logger.info('Order processed', { orderId: order.id });
}

// ✅ GOOD: Each function does one thing
async function processOrder(order: Order): Promise<ProcessedOrder> {
  validateOrder(order);
  const totals = calculateTotals(order.items);
  const savedOrder = await saveOrder(order, totals);
  await notifyCustomer(savedOrder);
  return savedOrder;
}

function validateOrder(order: Order): void {
  if (!order.items.length) throw new ValidationError('Order cannot be empty');
  if (order.total < 0) throw new ValidationError('Total cannot be negative');
}

function calculateTotals(items: OrderItem[]): OrderTotals {
  const subtotal = items.reduce((sum, item) => sum + item.price * item.quantity, 0);
  const tax = subtotal * TAX_RATE;
  return { subtotal, tax, total: subtotal + tax };
}
```

### Parameter Rules

```typescript
// ❌ BAD: Too many parameters
function createUser(
  name: string, email: string, role: string,
  isActive: boolean, avatar: string, bio: string
) { ... }

// ✅ GOOD: Use an object for 3+ parameters
interface CreateUserInput {
  name: string;
  email: string;
  role?: UserRole;
  isActive?: boolean;
  avatar?: string;
  bio?: string;
}

function createUser(input: CreateUserInput): User { ... }

// ❌ BAD: Boolean parameter (caller can't read intent)
setVisible(true);

// ✅ GOOD: Named method instead
show();
hide();
```

---

## SOLID Principles (With Code)

### S — Single Responsibility

```typescript
// ❌ BAD: UserService does everything
class UserService {
  createUser() { ... }
  sendEmail() { ... }
  generateReport() { ... }
  uploadAvatar() { ... }
}

// ✅ GOOD: Separate concerns
class UserService { createUser() { ... } }
class EmailService { sendWelcomeEmail() { ... } }
class ReportService { generateUserReport() { ... } }
class AvatarService { upload() { ... } }
```

### O — Open/Closed

```typescript
// ❌ BAD: Adding a new type requires modifying existing code
function calculateDiscount(type: string, amount: number): number {
  if (type === 'student') return amount * 0.2;
  if (type === 'veteran') return amount * 0.15;
  if (type === 'senior') return amount * 0.1; // must modify for every new type
  return 0;
}

// ✅ GOOD: Open for extension, closed for modification
interface DiscountStrategy {
  calculate(amount: number): number;
}

class StudentDiscount implements DiscountStrategy {
  calculate(amount: number) {
    return amount * 0.2;
  }
}

class VeteranDiscount implements DiscountStrategy {
  calculate(amount: number) {
    return amount * 0.15;
  }
}

// New types = new class, no existing code changes
class EmployeeDiscount implements DiscountStrategy {
  calculate(amount: number) {
    return amount * 0.25;
  }
}
```

### D — Dependency Inversion

```typescript
// ❌ BAD: High-level module depends on low-level concrete
class OrderService {
  private db = new MySQLDatabase(); // coupled to MySQL
  private mailer = new SendGridMailer(); // coupled to SendGrid
}

// ✅ GOOD: Depend on abstractions (interfaces)
interface Database {
  save(data: unknown): Promise<void>;
}
interface Mailer {
  send(to: string, body: string): Promise<void>;
}

class OrderService {
  constructor(
    private db: Database, // can be MySQL, Postgres, in-memory
    private mailer: Mailer, // can be SendGrid, SES, mock
  ) {}
}
```

---

## Error Handling

```typescript
// ❌ BAD: Swallowing errors
try {
  await saveUser(user);
} catch (e) {
  // silence
}

// ❌ BAD: Generic catch-all
try {
  await processPayment(order);
} catch (e) {
  console.log('Something went wrong');
}

// ✅ GOOD: Handle specific errors, propagate unexpected
try {
  await processPayment(order);
} catch (error) {
  if (error instanceof InsufficientFundsError) {
    return { success: false, message: 'Insufficient funds' };
  }
  if (error instanceof PaymentGatewayError) {
    logger.warn('Payment gateway unavailable, queuing for retry', { orderId: order.id });
    await retryQueue.add(order);
    return { success: false, message: 'Payment processing delayed' };
  }
  throw error; // unexpected error — let it propagate
}
```

---

## Comments

```typescript
// ❌ BAD: Comments that restate the code
// Increment i by 1
i++;

// Set the user's name
user.name = newName;

// Check if user is active
if (user.isActive) { ... }

// ✅ GOOD: Comments that explain WHY, not WHAT
// Tax exemption expires after 365 days per IRS Publication 334
const isExempt = daysSinceRegistration < 365;

// Using binary search here because the list is pre-sorted and
// can contain 100K+ items. Linear search caused P95 > 2s.
const index = binarySearch(sortedItems, target);

// Retry 3 times because the payment gateway has transient 503s
// during their daily maintenance window (02:00-02:15 UTC)
const result = await withRetry(() => chargeCard(amount), { maxRetries: 3 });
```

---

## Code Smells → Refactoring

```
Smell                    → Refactoring
───────────────────────────────────────
Long function (>30 lines) → Extract method
Deep nesting (>3 levels)  → Early return / guard clauses
Duplicate code            → Extract shared function
Magic numbers             → Named constants
Boolean parameters        → Separate methods or options object
God class (>300 lines)    → Split into focused classes
Feature envy              → Move method to appropriate class
Primitive obsession       → Value objects (Email, Money, UserId)
Long parameter list       → Parameter object
```

```typescript
// Deep nesting → Early return
// ❌ BAD
function processUser(user: User) {
  if (user) {
    if (user.isActive) {
      if (user.hasPermission('edit')) {
        // actual logic buried 3 levels deep
        doStuff();
      }
    }
  }
}

// ✅ GOOD: Guard clauses — fail fast, keep happy path unindented
function processUser(user: User) {
  if (!user) return;
  if (!user.isActive) return;
  if (!user.hasPermission('edit')) return;

  doStuff(); // happy path at top level
}
```

## 🚨 Edge-Case & Failure Mode Matrix

| Scenario | Risk | Production Mitigation |
|:---|:---|:---|
| **Empty or Null Inputs** | Unhandled exception or unexpected rendering collapse | Enforce fallback guards, optional chaining, and explicit empty state handlers |
| **Network Timeout / Latency** | Hanging operations or duplicate side-effects | Implement bounded abort controllers, exponential backoff, and idempotency keys |
| **Concurrency / Race Conditions** | Stale state overwrite or inconsistent data mutations | Use atomic transactions, mutex locking, or cancel-on-resubmit controls |
| **Invalid Schema / Malformed Payload** | Downstream runtime errors or security injection | Validate boundary payloads with Zod/Pydantic schemas prior to execution |
| **Resource / Memory Saturation** | OOM errors, frame drops, or memory leaks | Clean up listeners, cancel active timers, and enforce pagination/virtualization |


## 🏛️ Tribunal Verification & Guardrails

**Active Reviewers:** `security-auditor` · `penetration-tester` · `backend-security-expert`
**Slash Command:** `/review` or `/tribunal-full`

### 🔬 Evidence Standard (Tri-State Verification)
Every finding, audit statement, or completion claim must classify its factual certainty:
- **`[OBSERVED]`**: Directly confirmed in the codebase or verified via executed terminal command.
- **`[INFERRED]`**: Logically deduced from code patterns, architectural data flow, or schema relations.
- **`[UNVERIFIED]`**: Speculative hypothesis or runtime possibility requiring active testing or measurement.

### ✅ Pre-Flight Self-Audit Checklist
```
✅ Are user inputs sanitized and treated as untrusted data at system boundaries?
✅ Are secrets loaded strictly via environment variables with zero hardcoding?
✅ Is least-privilege enforcement active on APIs, tokens, and storage buckets?
✅ Are prompt-injection delimiters and sanitizers wrapped around LLM inputs?
✅ Did I verify encryption in transit and at rest for sensitive data?
```

### 🛑 Verification-Before-Completion (VBC) Protocol
**CRITICAL:** You must follow a strict "evidence-based closeout" state machine.
- ❌ **Forbidden:** Declaring a task complete because the output "looks correct."
- ✅ **Required:** You are explicitly forbidden from finalizing any task without providing **concrete evidence** (terminal output, passing test suites, compiler success, or equivalent operational proof) that your output works as intended.