Rust port of OmniVox, wire-compatible with the C++ original

Byte-exact cereal binary layout, RFC 8439 ChaCha20-Poly1305, RFC 7914
scrypt defaults; tokio transport preserving the original's observable
behavior (contract B1-B3, B5 quirks included). Parity evidence: golden
C++ vectors in tests/vectors.rs and loopback behavior tests; both
cross-directions verified against the unmodified C++ binaries.

Source: https://git.0xfeedc0de.com/michael/OmniVox

examples/common/mod.rs

@@ -0,0 +1,37 @@
+//! Port of the C++ `common.h`: shared payload type and demo constants.
+
+use omnivox::{Cereal, CodecError, Reader, write_byte_vec};
+
+/// Wire-identical to the C++ `DatagramPayload` (cereal field order:
+/// `id`, `v1.qword`, `payload`; the `PackedValue64` union only ever
+/// serialized its `qword`, so it ports as a plain `u64`).
+#[derive(Debug, Default)]
+pub struct DatagramPayload {
+    pub id: u16,
+    pub v1: u64,
+    pub payload: Vec<u8>,
+}
+
+impl Cereal for DatagramPayload {
+    fn encode(&self, out: &mut Vec<u8>) {
+        out.extend_from_slice(&self.id.to_le_bytes());
+        out.extend_from_slice(&self.v1.to_le_bytes());
+        write_byte_vec(out, &self.payload);
+    }
+
+    fn decode(bytes: &[u8]) -> Result<Self, CodecError> {
+        let mut r = Reader::new(bytes);
+        Ok(Self {
+            id: r.u16()?,
+            v1: r.u64()?,
+            payload: r.byte_vec()?,
+        })
+    }
+}
+
+pub const PASSWORD: &str = "SecurePassword123";
+pub const SALT: &[u8] = &[0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08];
+pub const SERVER_PORT: u16 = 8080;
+/// Only used by the client example.
+#[allow(dead_code)]
+pub const SERVER_ADDR: &str = "127.0.0.1";