.agents/skills/tdd/deep-modules.md
From "A Philosophy of Software Design":
Deep module = small interface + lots of implementation
┌─────────────────────┐
│ Small Interface │ ← Few methods, simple params
├─────────────────────┤
│ │
│ │
│ Deep Implementation│ ← Complex logic hidden
│ │
│ │
└─────────────────────┘
Shallow module = large interface + little implementation (avoid)
┌─────────────────────────────────┐
│ Large Interface │ ← Many methods, complex params
├─────────────────────────────────┤
│ Thin Implementation │ ← Just passes through
└─────────────────────────────────┘
When designing interfaces, ask: