The job you were hired into changed while you were in it. Your agent writes the migration, the validation and the glue faster than you would, at any hour. So most of the code you are accountable for this year is code you read rather than code you wrote. That is a different skill from the one you were hired on, and it fails in a different way. It also removes the thing that used to build judgment for free. You can now ship a correct change to a system you could not draw on a napkin, and nothing in your week raises a hand. This book has a name for what accumulates: comprehension debt, meaning code you are accountable for and cannot explain. What is new is not that it exists. It is how fast you can take it on.
This is a field guide, indexed by the situation in front of you rather than by syllabus. Twenty-five chapters, and every one written to you ends in an exercise small enough for a Wednesday afternoon and never contingent on a manager saying yes. It rests on a small canon that predates the agent and will outlast it: Parnas on what a module should hide, Feathers on changing code that nothing tests, Evans on the word the business uses for a thing. The test for anything in here is whether the skill transfers to the next model, the next codebase and the next job. You do not need a job to use it. Most chapters also carry two short blocks, one for the engineer who already runs the move and one for whoever is mentoring them, and the last chapter is written for the person who runs hiring.
The cost, stated up front: about three and a half hours a week if you run all of it. There is a smaller version that costs a minute a change, and it is the part I would protect if everything else went. No book hands anybody judgment. What this one gives you is the vocabulary, the exercises and the order to run them in. The practice has to be yours, on code somebody is actually going to run. Seniority here is not tenure and it is not a title. It is what you are the last check on, and it is what you keep when the tools change again.
