Closing thought

Intelligence is expensive.
Determinism is cheap.
Spend the first only where the second cannot do the job.

Twenty-one parts, one discipline. Parse before you prompt. Index before you search. Traverse before you reason. Validate before you accept. Decide authority before the agent asks. Record what happened in a form someone else can read. Measure all of it.

The model is the most capable component in the stack and the most expensive one to call. Treat each call the way you treat any scarce resource: schedule it deliberately, feed it only what it needs, and account for what it did.

If this book changes one habit, make it this one. Before each model call your system makes, ask what part of it code could have done. Before each action your agent takes, ask who decided it may. In both cases the answer should already be written down.