| Layer | Framework | Question It Answers |
|---|---|---|
| 5 | Mental Model (F1) | How should I think about this? |
| 4 | Principle (F2) | What engineering rule applies? |
| 3 | Tradeoff (F4) | What am I giving up? |
| 2 | Law (F9) | What constraint is non-negotiable? |
| 1 | Review Questions (F5) | Have I checked every angle? |
Use: Before any architecture decision, walk the stack top to bottom. The layer where you cannot answer is where the decision is under-informed.