Protocol types for smolvm host-guest communication.

This crate defines the wire protocol for vsock communication between the smolvm host and the guest agent (smolvm-agent).

Protocol Overview

Communication uses JSON-encoded messages over vsock. Each message is prefixed with a 4-byte big-endian length header.

+----------------+-------------------+
| Length (4 BE)  | JSON payload      |
+----------------+-------------------+