This is the core of the matter though, knowing what you need to understand and what you can ignore is the actual programmer's skill. It requires you to have a clear mental picture of both what you are trying to build and what the underlying machine will do when you are finished.
You need to understand the abstractions, but also where they leak, when they won't match reality, and how. This is why knowing computer architecture and assembly helps you to optimize your code even if you are coding in a high level language.
The problem with coding agents is that they are tuned to work on all contexts so they always fill an underspecified request by optimizing the average case and often without stating all the assumptions that they make. So you still need to understand what you specified and what got filled in automagically by the agent. My experience is that they (even the paid frontier models) are poor judges of the most important assumptions they make, which will might be corrected by a prompt or a tool output in which case it is fine. Otherwise it will be ignored and steer the model into a weird loop. It then tries to fix things but can not do so since its mental model is totally broken now.
Do not get me wrong, I am so happy to let the agent handle tool building (especially those that involve a web UI) and fill in the CLI command line argument parser. But every time I trust the agent by relying on it to drive the mental model of what we are doing, I got seriously bitten. Well, maybe that should not be surprise me, but I can understand the confusion of less experienced programmers and non-coders. It must really be frustrating to be able to build so much, but also not to be able to fix seemingly small issues.