Which object have my association extension method?

My Stackoverflow question:

I have an association extension method like the following:

class Bundle < ActiveRecord::Base
has_many :items do
def foo
end
end

I was trying to use delayed job/sidekiq delay() method like the
following:

b.items.delay.foo

But I can’t. You see, when delay is called, association evaluated
immediately to an array of records. That array does not have the
association extension methods.

So I tried to see if b.items.proxy_association, has my extension
methods,
and to my surprise, foo() is not there either.

Which object does my foo() method sit in?