Design Principles

• Scope: SOLID principles for OOP/architecture design
• Load if: Starting new feature, refactoring, architecture review
• Prerequisites: @smith-principles/SKILL.md (fundamental principles: DRY, KISS, YAGNI, MECE)

SOLID Principles

• Single Responsibility: One reason to change per class/module
• Open/Closed: Open for extension, closed for modification
• Liskov Substitution: Subtypes must be substitutable for base types
• Interface Segregation: Many specific interfaces over one general
• Dependency Inversion: Depend on abstractions, not concretions