Chapter 9 is your decision timeline. It records the important architectural choices you made along the way, so you can see what was decided, why, and which options were not picked. This chapter often starts small, but it grows as the system grows. In this article I explain what belongs in chapter 9, what to keep out, a minimal structure you can copy, plus a small example from Pitstop.

Chapter 4 opens the "How is it built and how does it run" group. It is where goals, constraints, and context from the first three chapters start to shape the design through a small set of guiding decisions. In this article I show what belongs in chapter 4, what to keep out, how to handle open strategy questions, and a flexible structure you can copy, plus a small example from Pitstop.

Chapter 2 lists the non-negotiables that shape your design space. If you do not write these down early, they will still exist, but they will surprise you later. In this article I show what belongs in chapter 2, what to keep out, and a minimal structure you can copy, plus a small example from Pitstop.