https://pkg.go.dev/net#Resolver.LookupSRV has signature:

func (r *Resolver) LookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error)

... but the docs don't make it super clear what that string result is.

There's a hint in the docs:

LookupSRV constructs the DNS name to look up following RFC 2782. That is, it looks up _service._proto.name.

But that makes it sound like it's an implementation detail, not that the first result is indeed that DNS name.