bishare-protocol

The BIShare wire protocol as a standalone Rust crate: device discovery records, message framing, X25519 key agreement, AES-256-GCM sealing with per-transfer keys, and the BSE2 container used for encrypted links. It is the single implementation shared by all five platform builds through flutter_rust_bridge, and it ships test vectors that the browser client (WebCrypto) verifies against, so the two implementations cannot drift apart.