This order is conveniently pinned as a short durable contract for the agent, so as not to spell it out every time. It fits in a few lines: reproduce without changing production code, show the causal chain from the entry to the failure, name a refuting observation for each hypothesis and only then propose a minimal patch and a regression test. Such a contract keeps debugging in the right sequence even under the pressure of "let's just fix it faster".

The cost of a broken order is asymmetric and insidious. An edit made before the cause is confirmed sometimes "works" - the symptom disappears - and that is a worse outcome than an outright failure: the cause remains, and the signal about it you have just silenced. The bug will return in another place, under another symptom, and it will be hard to link it to this edit. The time saved on diagnosis returns with interest as a floating defect. This hits autonomous work especially hard: an agent allowed to fix the symptom will confidently close the task as done, and the chain of consequences surfaces later without it and without the context in which it was easy to untangle.

This does not mean every typo must be carried through the full protocol. For a defect with an obvious, single cause the reproduction and the edit converge into one step. The protocol pays off where the symptom is unstable, the causes may be several, or the bug floats between runs: the less obvious the cause, the more expensive it is to guess and the cheaper it is to reproduce first.

You should check not only the disappearance of the symptom but the quality of the proof of the cause. The right check is a regression test that failed before the edit and passes after: it shows that you addressed the cause itself rather than masked the symptom. If such a test cannot be built, the cause is most likely not confirmed - you are observing a coincidence, not an established link, and it is too early to rejoice at the green screen. A useful control question before closing: can I name the cause in one phrase and show the observation that confirmed it. No such phrase means you saw the symptom disappear, not the cause removed.

The typical failures repeat the skipped steps. No reproduction - the fix is made by description and misses. No refuting observations - the first hypothesis is clung to and confirmed by oneself. No regression test - the same bug returns a month later as new. The sign of all of them is the same: the code was changed before the cause was named and confirmed. Reproduction and cause first, then the edit; otherwise you treat not the disease but its shadow.