separation of concerns. This cannot be extended
            for user defined server contexts.
          </li>
<li class="listitem">
            The "cancellation token" is stored inside the message. This
            breaks the separation of concerns.
          </li>
<li class="listitem">
            The <code class="computeroutput"><span class="identifier">_reply_impl</span></code> function
            implies that the message implementation also shares responsibility for
            the means of sending ba