Why do we need Ai agent? Automation can be done by code

[JianguoChuan]

Coding can be done by ai, and automation can be done easily by codes, why do we need a ai agent to do that?
Furthermore, ai's behavior is not predictable sometimes, how can we trust the ai agent?
I am quite confused, ai can help you to search, summarise, but definitely not the real work, decision and automation of works. Nobody can predict their behavior and trust the final results.