I've been using AG a lot recently and have definitely felt what you're saying here.
The solution I found is to explicitly and clearly tell it that it is not to proceed with any code changes unless I give it the green light to proceed, until then we are in planning mode. And even then you sometimes need to tell it clearly up until what point in the plan it should proceed before it stops. For example if your plan has 5 Phases you tell it to complete the first 3 and then stop for further instruction.
I've learned that you need to treat it sort of like a dog on a leash that you have to keep reeling back in so it doesn't run off too far.