feat(project): Establish initial IRTT workspace and protocol definitions

Set up the multi-crate project structure and add the core IRTT protocol with pinned dependencies for reproducible builds.

crates/irtt-proto/src/lib.rs

@@ -0,0 +1,52 @@
+#![forbid(unsafe_code)]
+
+pub mod close;
+pub mod echo;
+pub mod error;
+pub mod flags;
+pub mod hmac;
+pub mod layout;
+pub mod open;
+pub mod params;
+pub mod varint;
+
+pub use close::{encode_close_request, CloseRequest};
+pub use echo::{decode_echo_reply, encode_echo_request, EchoReply, EchoRequest, TimestampFields};
+pub use error::{ProtoError, Result};
+pub use flags::*;
+pub use hmac::{compute_hmac, compute_hmac_in_place, verify_hmac};
+pub use layout::{echo_header_len, echo_packet_len, PacketLayout};
+pub use open::{decode_open_reply, encode_open_request, OpenReply, OpenRequest};
+pub use params::{Clock, Params, ReceivedStats, ServerFill, StampAt};
+
+pub const MAGIC: [u8; 3] = [0x14, 0xA7, 0x5B];
+pub const PROTOCOL_VERSION: i64 = 1;
+
+pub const HMAC_SIZE: usize = 16;
+pub const TOKEN_SIZE: usize = 8;
+pub const SEQ_SIZE: usize = 4;
+pub const RECV_COUNT_SIZE: usize = 4;
+pub const RECV_WINDOW_SIZE: usize = 8;
+pub const TIMESTAMP_SIZE: usize = 8;
+
+pub(crate) const HEADER_SIZE: usize = 4;
+
+pub(crate) fn write_header(out: &mut Vec<u8>, flags: u8) {
+    out.extend_from_slice(&MAGIC);
+    out.push(flags);
+}
+
+pub(crate) fn validate_header(packet: &[u8]) -> Result<u8> {
+    if packet.len() < HEADER_SIZE {
+        return Err(ProtoError::PacketTooShort {
+            needed: HEADER_SIZE,
+            actual: packet.len(),
+        });
+    }
+    if packet[..3] != MAGIC {
+        return Err(ProtoError::BadMagic);
+    }
+    let flags = packet[3];
+    flags::validate_flags(flags)?;
+    Ok(flags)
+}