Copilot is pretty good at recognizing and generating the error check ; it will even propose error messages for you. Clearly you may want to change it to your specific case. So I don’t think dev time will be significantly slower. My experience has been positive. I think the go plugin also has some helpers for this pattern, but I don’t recall exactly how they work.

nope

error handling (as expressed here) is equivalent in priority to core business logic

it absolutely belongs in source, because it is important for developers to see