The first three sections are about how you work. This one is about the thing itself. An application is a small number of parts that always show up: something the user sees, something that runs on a server, somewhere the data lives, a way to tell who is logged in, and a handful of other companies' services doing the work you did not want to build.
You can direct an AI to write all of it without knowing any of this. What you cannot do is decide. Which part should hold this data, whether that key is safe where you just put it, why the page broke, whether the fix an assistant just proposed is a fix or a hole. Eight sections, each one aimed at a decision you will have to make.
- The shape of a web app
- Choosing a stack you can finish
- The interface people actually touch
- Where data lives
- Databases without the theory
- Accounts and logging in
- Connecting other services
- Email, files and background work
These eight get you to something that works. They do not get you to something safe to put in front of other people: the access rules, the leaked keys and the data you are allowed to keep are section 5, and it comes straight after this one for a reason. Build here. Check there. Then ship.