How is a communication protocol a mechanism?
The view of Alice is what Alice gets to see; it is a probability distribution that depends on the inputs of both players $x,y$. It is a distribution over triples $(x,\tau,r_A)$, where $x$ is Alice's input, $\tau$ is the transcript of the protocol, and $r_A$ is Alice's private randomness. This probability distribution depends both on $x$ and on Bob's input $y$.

Here is how to generate this probability distribution, given a protocol $P$ and the inputs $x,y$ of both players. Generate the shared randomness $r$ according to its distribution, and Alice's private randomness $r_A$ according to its distribution. Run $P$, obtaining a transcript $\tau$. Output $(x,\tau,r_A)$.