It looks like you're attributing human intentions to a machine, that can't be healthy. You're also dismissing how humans routinely lie, deflect blame (especially when their job is at stake), or fail to learn for a myriad of valid reasons.
Agents don't "sneak in" bad code, or "lie". They get shit wrong sometimes, or they get lazy at the tail end of a long task, which are not categorically new things in software development. Even excellent engineers do it. If your only response to that is to say "yeah but i can fire them" then you are a bad lead. Just some corpo mid-manager eager to push blame and consequences at your underlings instead of creating a system that allows them to perform within their individual limitations.
You're right that they don't learn in that the model doesn't re-weight itself based on your feedback but that one is so trivially solved that it's not even a subject. Haven't you ever worked with brilliant stoner/creative types ? They forget shit all the time so you learn to write everything down and devise stratagems so the relevant information they keep forgetting is pushed to the front of their mind regularly. Well, i'd do that, but you'd just fire them on the spot i guess.
My point is : on the one hand you're overestimating the failure modes of AI, and on the other hand you're dismissing the failure modes of humans. With the added simplistic authoritarian thinking "i'd fire them anyways if they don't behave".