interface message complexity

The current interface allows us to only send one message between a shim and the core. This provides us with a really simple way of interactions definition.

The complexity is however hidden in the message itself. Every message serves multiple purposes and when the message is received the core and shim need to unpack it and process each part separately and for certain parts in a real specific order.
Because the message serves a number of purposes it has a large overhead. This might not show up in the code directly as the heavy lifting is done in the generated code. It will show up in the amount of data as a message, even if it does not have all fields, still needs to be encoded in a way that it unpacks correctly on the other side.

The trade off between having one message with a simple interface or multiple more focussed messages with a slightly more complex interface needs to be assessed.