Not totally sure how we got to this state, but we got many crashes where FakeBraintree.registry.payment_methods[nonce] was nil and therefore couldn't merge. This is the dumbest fix possible, but it works.
Before the asset versions needed to specified in lib/fake_braintree/version.rb
Now the most recent client code is downloaded and loaded into a capybara session
so that the dropin version may be extracted.