❌ NO behavior changes → refactoring only ❌ NO applying without approval ❌ NO generic names (data, temp, obj, x) ✅ MUST show before/after diffs ✅ MUST explain why each change improves code ✅ MUST verify tests pass after each change </critical_constraints> 1. **Rename**: Use descriptive names conveying intent 2. **Extract**: Break large functions into single-responsibility units 3. **Flatten**: Replace nesting with guard clauses/early returns 4. **DRY**: Consolidate repeated code into reusable functions 5. **Simplify**: Replace complex conditionals with lookup tables ## Flatten Nesting (Guard Clauses) ```python # Before: deep nesting if user: if user.is_active: if user.has_permission('edit'): # logic

After: guard clauses

if not user: return False
if not user.is_active: return False
if not user.has_permission('edit'): return False

logic

## Extract Function
```javascript
// Before: all-in-one
function handleOrder(order) { /* validate, calc, discount */ }

// After: composed
function handleOrder(order) {
    validateOrder(order);
    const subtotal = calculateSubtotal(order.items);
    return applyDiscount(subtotal, order.discountCode);
}

- Function >20 lines → extract smaller functions - Nesting >3 levels → use guard clauses - Same code in 2+ places → extract to shared function - Single-letter variables → rename to descriptive