Claude lied to me I think. The issue turned out to be that in Go you can't extend structs that come from a library with additional methods. Here's what Claude told me though:
> The issue is that Go's compiler processes files in a package in lexicographical order. Since instance.go comes before util.go alphabetically, the Has method defined in util.go isn't available yet when instance.go is being compiled.
> You need to move the method definition to a file that comes alphabetically before instance.go, or rename one of the files. The easiest solution is to move the Tags methods to a separate file or rename util.go to something like aaa_util.go or extensions.go.
