Per-VM gRPC relay: listens on a host Unix-domain socket and for each inbound connection performs the Firecracker vsock CONNECT/OK handshake via RelayDialer, then pipes bytes bidirectionally until either side closes.

Process topology:

• The GenServer owns the listen socket and spawns a linked acceptor process via handle_continue. The acceptor blocks on :socket.accept without blocking the GenServer itself.
• Each accepted connection spawns an unlinked connection process that calls RelayDialer.dial/3 then spawns two linked+monitored pipe workers (one per direction). The link ensures a connection handler death reaps both workers; the monitor lets the handler react to a worker's normal end and close both sockets cleanly. When either worker ends, the handler unlinks the sibling before killing it so the resulting :killed exit does not cascade back to the handler via the link.
• terminate/2 closes the listen socket (which causes the acceptor to exit on its next accept call) and removes the socket file so a subsequent start_link with the same path can rebind.