I'm sorry, but this is selling good engineers very short. If you didn't nest your utils folder 8 folders deep, it seems pretty obvious that one should check the utils folder before writing another utility function. This stuff should also be caught in code reviews. Maybe the new guy didn't know that util function existed, but surely you did when you reviewed their MR? Obviously mistakes like that can happen, but I've found that to be the exception rather than the rule, even in some of the gnarlier codebases I've worked in.