Shown up by the test StandaloneCordaRPClientTest::attachments
This used to work when the RPC framework used Kryo, however, it cannot work now because WrapperStream, the type being serialized, won't exist on the node. This causes the carpenter to be invoked because we apply a strict failure of type loading to generate a carpentry step. However, under Kryo the intention was to allow any bytes stream to be serialized and deserialized either end regardless of meta type. So, we could look at changing the carpenter to check the scheme source of the type and allow a downgrade to that. Equally, we might not. Requires some thought either way.
For now, I've ignored the test and added a standard attachment test that doesn't wrap the stream with a custome type