In Figure 4, the labels "Recipient/Intermediary" and "Recpipient/Intermediary $process-message endpoint" are confusing. Is this trying to indicate that the http response or the additional query may come from either the intermediary or the ultimate recipient? I suggest having separate figures for when the intermediary exists and when it is a direct operation. It's not clear from the figure or the accompanying text what the expectations are for the intermediary with respect to the http response.