Sanstun: A sans-IO, parallel-friendly WireGuard implementation in Rust

Firezone has released sanstun, a new sans-IO Rust implementation of the WireGuard state machine designed for parallel processing and security. The sans-IO architecture separates input/output operations and side effects from business logic, making the code easier to test and compose while avoiding issues like function coloring. Sanstun was developed after over two years of patching the boringtun WireGuard library, during which the team identified key limitations such as automatic session establishment and internal buffering that warranted a cleaner API design.