diff --git a/unshell-protocol/src/error.rs b/unshell-protocol/src/error.rs
index 43f6858..3db9ac1 100644
--- a/unshell-protocol/src/error.rs
+++ b/unshell-protocol/src/error.rs
@@ -89,18 +89,15 @@ pub enum SerializeError {
     /// The packet path contains more bytes than the frame length field can represent.
     PathTooLarge,
 
-    /// The procedure identifier is too large to encode in a `u32` length field.
-    ProcIdTooLarge,
-
     /// The body section is too large to encode in a `u32` length field.
     BodyTooLarge,
 }
 
 /// Errors produced while parsing a [`Packet`] from untrusted wire bytes.
 ///
-/// Deserialization rejects partial, inconsistent, or invalid UTF-8 frames before
-/// endpoint routing sees them. Keeping these separate from route failures makes it
-/// clear whether a packet failed before or after it became structured data.
+/// Deserialization rejects partial or inconsistent frames before endpoint routing
+/// sees them. Keeping these separate from route failures makes it clear whether a
+/// packet failed before or after it became structured data.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum DeserializeError {
     /// The buffer ended before the parser could read the required field.
@@ -111,12 +108,6 @@ pub enum DeserializeError {
 
     /// The path length overflowed while computing the path byte range.
     PathTooLong,
-
-    /// The procedure id length overflowed while computing the body byte range.
-    ProcIdTooLong,
-
-    /// The encoded procedure id was not valid UTF-8.
-    InvalidUtf8,
 }
 
 impl From<SerializeError> for EndpointError {
diff --git a/unshell-protocol/src/packet.rs b/unshell-protocol/src/packet.rs
index 7f5926a..37d6699 100644
--- a/unshell-protocol/src/packet.rs
+++ b/unshell-protocol/src/packet.rs
@@ -1,47 +1,54 @@
 extern crate alloc;
 
-use alloc::string::String;
 use alloc::vec::Vec;
 
 use crate::{DeserializeError, SerializeError};
 
+/// Fully decoded UnShell test packet.
+///
+/// The current protocol tests route only on hook id, hook end state, and absolute
+/// path. `procedure_id` is therefore a compact numeric contract id instead of a
+/// string label; application code can maintain its own id-to-name table outside the
+/// hot packet path if it needs human-readable names.
 #[derive(Debug)]
 pub struct Packet {
     pub hook_id: u16,
     pub end_hook: bool,
     pub path: Vec<u32>,
-    // ── body (routers never read below this line) ──
-    pub procedure_id: String,
+    pub procedure_id: u32,
     pub data: Vec<u8>,
 }
 
-/// Returned by `deserialize_header` — only what a router needs.
-/// `body_remainder` is a raw slice into the original buffer so the
-/// entire body can be forwarded without touching it.
-#[derive(Debug)]
-pub struct HeaderRef<'buf> {
-    pub hook_id: u16,
-    pub end_hook: bool,
-    pub path: &'buf [u32],
-    pub body_remainder: &'buf [u8],
-}
-
 impl Packet {
+    /// Serializes the packet into the crate's current little-endian frame format.
+    ///
+    /// Layout:
+    /// - fixed header: `hook_id: u16`, `flags: u8`, padding, `path_len: u32`
+    /// - path: `path_len` little-endian `u32` segments
+    /// - body: `body_len: u32`, `procedure_id: u32`, raw `data`
+    ///
+    /// Keeping `procedure_id` fixed-width removes the old string length and UTF-8
+    /// validation path. That makes deserialization a single full-packet parse,
+    /// which matches how the endpoint mock transports actually consume packets.
     pub fn serialize(&self) -> Result<Vec<u8>, SerializeError> {
-        let proc_id_bytes = self.procedure_id.as_bytes();
+        let path_len = u32::try_from(self.path.len()).map_err(|_| SerializeError::PathTooLarge)?;
 
-        let path_len = self.path.len() as u32;
-        let proc_id_len =
-            u32::try_from(proc_id_bytes.len()).map_err(|_| SerializeError::ProcIdTooLarge)?;
-
-        // body = proc_id_len field + proc_id bytes + data bytes
+        // body = fixed procedure_id field + data bytes
         let body_payload_len = 4usize
-            .checked_add(proc_id_bytes.len())
-            .and_then(|n| n.checked_add(self.data.len()))
+            .checked_add(self.data.len())
             .ok_or(SerializeError::BodyTooLarge)?;
         let body_len = u32::try_from(body_payload_len).map_err(|_| SerializeError::BodyTooLarge)?;
 
-        let total = 8 + (self.path.len() * 4) + 4 + body_payload_len;
+        let path_bytes = self
+            .path
+            .len()
+            .checked_mul(4)
+            .ok_or(SerializeError::PathTooLarge)?;
+        let total = 8usize
+            .checked_add(path_bytes)
+            .and_then(|n| n.checked_add(4))
+            .and_then(|n| n.checked_add(body_payload_len))
+            .ok_or(SerializeError::BodyTooLarge)?;
         let mut buf = Vec::with_capacity(total);
 
         // ── header ────────────────────────────────────────────────────────────
@@ -56,16 +63,19 @@ impl Packet {
 
         // ── body ──────────────────────────────────────────────────────────────
         buf.extend_from_slice(&body_len.to_le_bytes());
-        buf.extend_from_slice(&proc_id_len.to_le_bytes());
-        buf.extend_from_slice(proc_id_bytes);
+        buf.extend_from_slice(&self.procedure_id.to_le_bytes());
         buf.extend_from_slice(&self.data);
 
         Ok(buf)
     }
 
-    /// Deserialize only the header — O(path_len), body bytes are never read.
-    /// A router can inspect `HeaderRef` then forward the original buffer as-is.
-    pub fn deserialize_header(buf: &[u8]) -> Result<HeaderRef<'_>, DeserializeError> {
+    /// Deserializes a full packet from untrusted transport bytes.
+    ///
+    /// This parser intentionally consumes the complete packet shape. The old
+    /// partial parse path was removed because current routing tests and mock
+    /// transports always deserialize before calling endpoint routing, so keeping a
+    /// borrowed header API only preserved unused unsafe casting complexity.
+    pub fn deserialize(buf: &[u8]) -> Result<Self, DeserializeError> {
         // fixed prefix: hook_id (2) + flags (1) + padding (1) + path_len (4)
         if buf.len() < 8 {
             return Err(DeserializeError::BufferTooShort);
@@ -85,25 +95,13 @@ impl Packet {
             return Err(DeserializeError::BufferTooShort);
         }
 
-        // Cast the buffer slice to a u32 slice.
-        // This requires alignment. rkyv handles this, but for a manual cast:
-        let path_ptr = buf[path_start..path_end].as_ptr() as *const u32;
-        let path = unsafe { core::slice::from_raw_parts(path_ptr, path_len) };
-
-        Ok(HeaderRef {
-            hook_id,
-            end_hook,
-            path,
-            body_remainder: &buf[path_end..],
-        })
-    }
-
-    /// Full deserialization. Parses the header then the body.
-    pub fn deserialize(buf: &[u8]) -> Result<Self, DeserializeError> {
-        let header = Self::deserialize_header(buf)?;
-        let body_buf = header.body_remainder;
+        let mut path = Vec::with_capacity(path_len);
+        for chunk in buf[path_start..path_end].chunks_exact(4) {
+            path.push(u32::from_le_bytes([chunk[0], chunk[1], chunk[2], chunk[3]]));
+        }
 
         // body_len prefix
+        let body_buf = &buf[path_end..];
         if body_buf.len() < 4 {
             return Err(DeserializeError::BufferTooShort);
         }
@@ -117,31 +115,20 @@ impl Packet {
             return Err(DeserializeError::BodyLengthMismatch);
         }
 
-        // proc_id_len + proc_id
+        // procedure_id + data
         let inner = &body_buf[4..body_end];
         if inner.len() < 4 {
             return Err(DeserializeError::BufferTooShort);
         }
-        let proc_id_len = u32::from_le_bytes([inner[0], inner[1], inner[2], inner[3]]) as usize;
+        let procedure_id = u32::from_le_bytes([inner[0], inner[1], inner[2], inner[3]]);
 
-        let proc_id_start = 4usize;
-        let proc_id_end = proc_id_start
-            .checked_add(proc_id_len)
-            .ok_or(DeserializeError::ProcIdTooLong)?;
-        if inner.len() < proc_id_end {
-            return Err(DeserializeError::BufferTooShort);
-        }
-
-        let procedure_id = core::str::from_utf8(&inner[proc_id_start..proc_id_end])
-            .map_err(|_| DeserializeError::InvalidUtf8)?;
-
-        let data = inner[proc_id_end..].to_vec();
+        let data = inner[4..].to_vec();
 
         Ok(Self {
-            hook_id: header.hook_id,
-            end_hook: header.end_hook,
-            path: header.path.to_vec(),
-            procedure_id: procedure_id.into(),
+            hook_id,
+            end_hook,
+            path,
+            procedure_id,
             data,
         })
     }
diff --git a/unshell-protocol/src/tests/oneshot/streams.rs b/unshell-protocol/src/tests/oneshot/streams.rs
index 31c9045..299260a 100644
--- a/unshell-protocol/src/tests/oneshot/streams.rs
+++ b/unshell-protocol/src/tests/oneshot/streams.rs
@@ -1,6 +1,6 @@
 use crate::{Endpoint, Leaf, Packet};
 
-use alloc::{boxed::Box, format, string::ToString, vec, vec::Vec};
+use alloc::{boxed::Box, format, vec, vec::Vec};
 
 use super::support::{CommsLeaf, ENDPOINT_A, ENDPOINT_B, assert_hook_present, assert_hook_removed};
 
@@ -18,7 +18,7 @@ fn stream_open_packet(hook_id: u16) -> Packet {
         hook_id,
         end_hook: true,
         path: vec![ENDPOINT_A, ENDPOINT_B],
-        procedure_id: "stream.open".to_string(),
+        procedure_id: 2,
         data: b"open".to_vec(),
     }
 }
@@ -33,7 +33,7 @@ fn stream_frame_packet(hook_id: u16, index: usize, end_hook: bool) -> Packet {
         hook_id,
         end_hook,
         path: vec![ENDPOINT_A],
-        procedure_id: "stream.frame".to_string(),
+        procedure_id: 3,
         data: format!("stream-{index}").into_bytes(),
     }
 }
diff --git a/unshell-protocol/src/tests/oneshot/support.rs b/unshell-protocol/src/tests/oneshot/support.rs
index 6a0b8fd..c1ed4c1 100644
--- a/unshell-protocol/src/tests/oneshot/support.rs
+++ b/unshell-protocol/src/tests/oneshot/support.rs
@@ -1,6 +1,6 @@
 use crate::{Endpoint, Leaf, Packet};
 
-use alloc::{string::ToString, vec, vec::Vec};
+use alloc::{vec, vec::Vec};
 use crossbeam_channel::{Receiver, Sender};
 
 pub(super) const ENDPOINT_A: u32 = 0;
@@ -21,7 +21,7 @@ pub(super) fn echo_packet(path: Vec<u32>, hook_id: u16) -> Packet {
         hook_id,
         end_hook: true,
         path,
-        procedure_id: "echo".to_string(),
+        procedure_id: 1,
         data: "ABC123".as_bytes().to_vec(),
     }
 }
diff --git a/unshell-protocol/src/tests/packet.rs b/unshell-protocol/src/tests/packet.rs
index 754fa3f..83280db 100644
--- a/unshell-protocol/src/tests/packet.rs
+++ b/unshell-protocol/src/tests/packet.rs
@@ -1,4 +1,4 @@
-use alloc::{string::ToString, vec, vec::Vec};
+use alloc::{vec, vec::Vec};
 
 use crate::{DeserializeError, EndpointError, Packet, SerializeError};
 
@@ -9,7 +9,7 @@ fn make_packet() -> Packet {
         hook_id: 42,
         end_hook: false,
         path: vec![1, 2, 3],
-        procedure_id: "my.service.Method".to_string(),
+        procedure_id: 0xAABB_CCDD,
         data: vec![0xDE, 0xAD, 0xBE, 0xEF],
     }
 }
@@ -21,6 +21,15 @@ fn make_packet_flags(end_hook: bool) -> Packet {
     }
 }
 
+fn body_len_offset(buf: &[u8]) -> usize {
+    let path_len = u32::from_le_bytes([buf[4], buf[5], buf[6], buf[7]]) as usize;
+    8 + (path_len * 4)
+}
+
+fn procedure_id_offset(buf: &[u8]) -> usize {
+    body_len_offset(buf) + 4
+}
+
 // ── Round-trip ────────────────────────────────────────────────────────────
 
 #[test]
@@ -37,14 +46,16 @@ fn full_round_trip() {
 }
 
 #[test]
-fn header_round_trip() {
+fn procedure_id_is_fixed_width_u32() {
     let packet = make_packet();
     let buf = packet.serialize().unwrap();
-    let header = Packet::deserialize_header(&buf).unwrap();
+    let proc_offset = procedure_id_offset(&buf);
 
-    assert_eq!(header.hook_id, packet.hook_id);
-    assert_eq!(header.end_hook, packet.end_hook);
-    assert_eq!(header.path, packet.path);
+    assert_eq!(
+        &buf[proc_offset..proc_offset + 4],
+        &packet.procedure_id.to_le_bytes()
+    );
+    assert_eq!(&buf[proc_offset + 4..], packet.data.as_slice());
 }
 
 // ── Flags ─────────────────────────────────────────────────────────────────
@@ -52,17 +63,15 @@ fn header_round_trip() {
 #[test]
 fn flags_end_hook_false() {
     let packet = make_packet_flags(false);
-    let buf = packet.serialize().unwrap();
-    let header = Packet::deserialize_header(&buf).unwrap();
-    assert!(!header.end_hook);
+    let result = Packet::deserialize(&packet.serialize().unwrap()).unwrap();
+    assert!(!result.end_hook);
 }
 
 #[test]
 fn flags_end_hook_true() {
     let packet = make_packet_flags(true);
-    let buf = packet.serialize().unwrap();
-    let header = Packet::deserialize_header(&buf).unwrap();
-    assert!(header.end_hook);
+    let result = Packet::deserialize(&packet.serialize().unwrap()).unwrap();
+    assert!(result.end_hook);
 }
 
 // ── Empty fields ──────────────────────────────────────────────────────────
@@ -73,20 +82,18 @@ fn empty_path() {
         path: vec![],
         ..make_packet()
     };
-    let buf = packet.serialize().unwrap();
-    let header = Packet::deserialize_header(&buf).unwrap();
-    assert_eq!(header.path, &[] as &[u32]);
+    let result = Packet::deserialize(&packet.serialize().unwrap()).unwrap();
+    assert_eq!(result.path, &[] as &[u32]);
 }
 
 #[test]
-fn empty_procedure_id() {
+fn zero_procedure_id() {
     let packet = Packet {
-        procedure_id: "".to_string(),
+        procedure_id: 0,
         ..make_packet()
     };
-    let buf = packet.serialize().unwrap();
-    let result = Packet::deserialize(&buf).unwrap();
-    assert_eq!(result.procedure_id, "");
+    let result = Packet::deserialize(&packet.serialize().unwrap()).unwrap();
+    assert_eq!(result.procedure_id, 0);
 }
 
 #[test]
@@ -95,8 +102,7 @@ fn empty_data() {
         data: vec![],
         ..make_packet()
     };
-    let buf = packet.serialize().unwrap();
-    let result = Packet::deserialize(&buf).unwrap();
+    let result = Packet::deserialize(&packet.serialize().unwrap()).unwrap();
     assert_eq!(result.data, &[] as &[u8]);
 }
 
@@ -106,77 +112,16 @@ fn all_fields_empty() {
         hook_id: 0,
         end_hook: false,
         path: vec![],
-        procedure_id: "".to_string(),
+        procedure_id: 0,
         data: vec![],
     };
-    let buf = packet.serialize().unwrap();
-    let result = Packet::deserialize(&buf).unwrap();
+    let result = Packet::deserialize(&packet.serialize().unwrap()).unwrap();
     assert_eq!(result.hook_id, 0);
     assert_eq!(result.path, Vec::<u32>::new());
-    assert_eq!(result.procedure_id, "");
+    assert_eq!(result.procedure_id, 0);
     assert_eq!(result.data, &[] as &[u8]);
 }
 
-// ── Zero-copy: borrows point into the original buffer ─────────────────────
-
-#[test]
-fn header_path_is_borrowed_from_buffer() {
-    let buf = make_packet().serialize().unwrap();
-    let header = Packet::deserialize_header(&buf).unwrap();
-
-    let path_ptr = header.path.as_ptr() as *const u8;
-    let buf_range = buf.as_ptr_range();
-    assert!(
-        buf_range.contains(&path_ptr),
-        "path must be a subslice of the input buffer, not a new allocation"
-    );
-}
-
-#[test]
-fn body_remainder_is_borrowed_from_buffer() {
-    let buf = make_packet().serialize().unwrap();
-    let header = Packet::deserialize_header(&buf).unwrap();
-
-    let remainder_ptr = header.body_remainder.as_ptr();
-    let buf_range = buf.as_ptr_range();
-    assert!(
-        buf_range.contains(&remainder_ptr),
-        "body_remainder must point into the input buffer"
-    );
-}
-
-// ── Partial deserialization: body is untouched by header parse ────────────
-
-#[test]
-fn deserialize_header_does_not_read_body() {
-    let buf = make_packet().serialize().unwrap();
-    let header = Packet::deserialize_header(&buf).unwrap();
-
-    // Re-parse body from the remainder to confirm it's intact.
-    let body_buf = header.body_remainder;
-    let body_len =
-        u32::from_le_bytes([body_buf[0], body_buf[1], body_buf[2], body_buf[3]]) as usize;
-    assert!(
-        body_buf.len() >= 4 + body_len,
-        "body_remainder must contain the full body"
-    );
-}
-
-#[test]
-fn can_forward_buffer_after_header_parse() {
-    // Simulates a router: parse the header, then forward the raw buffer
-    // without touching the body.
-    let original = make_packet().serialize().unwrap();
-    let header = Packet::deserialize_header(&original).unwrap();
-
-    assert_eq!(header.path, &[1, 2, 3]);
-
-    // "Forward" by deserializing the full original buffer downstream.
-    let forwarded = Packet::deserialize(&original).unwrap();
-    assert_eq!(forwarded.procedure_id, "my.service.Method");
-    assert_eq!(forwarded.data, &[0xDE, 0xAD, 0xBE, 0xEF]);
-}
-
 // ── Truncation / corruption ───────────────────────────────────────────────
 
 #[test]
@@ -184,7 +129,7 @@ fn truncated_in_fixed_prefix() {
     let buf = make_packet().serialize().unwrap();
     // Cut inside the fixed 8-byte prefix.
     assert_eq!(
-        Packet::deserialize_header(&buf[..4]).unwrap_err(),
+        Packet::deserialize(&buf[..4]).unwrap_err(),
         DeserializeError::BufferTooShort
     );
 }
@@ -194,7 +139,18 @@ fn truncated_in_path() {
     let buf = make_packet().serialize().unwrap();
     // Cut to just past the fixed prefix, mid-path.
     assert_eq!(
-        Packet::deserialize_header(&buf[..9]).unwrap_err(),
+        Packet::deserialize(&buf[..9]).unwrap_err(),
+        DeserializeError::BufferTooShort
+    );
+}
+
+#[test]
+fn truncated_before_body_len() {
+    let buf = make_packet().serialize().unwrap();
+    let body_len_offset = body_len_offset(&buf);
+
+    assert_eq!(
+        Packet::deserialize(&buf[..body_len_offset + 2]).unwrap_err(),
         DeserializeError::BufferTooShort
     );
 }
@@ -203,27 +159,43 @@ fn truncated_in_path() {
 fn truncated_in_body() {
     let buf = make_packet().serialize().unwrap();
     // Remove last byte — well into the body.
-    assert!(Packet::deserialize(&buf[..buf.len() - 1]).is_err());
+    assert_eq!(
+        Packet::deserialize(&buf[..buf.len() - 1]).unwrap_err(),
+        DeserializeError::BodyLengthMismatch
+    );
 }
 
 #[test]
 fn empty_buffer_rejected() {
     assert_eq!(
-        Packet::deserialize_header(&[]).unwrap_err(),
+        Packet::deserialize(&[]).unwrap_err(),
         DeserializeError::BufferTooShort
     );
 }
 
 #[test]
-fn invalid_utf8_in_procedure_id() {
+fn body_length_mismatch_is_rejected() {
     let mut buf = make_packet().serialize().unwrap();
-    // Find where procedure_id starts: 8 + path_len*4 + 4 (body_len) + 4 (proc_id_len)
-    let path_len = u32::from_le_bytes([buf[4], buf[5], buf[6], buf[7]]) as usize;
-    let proc_id_offset = 8 + (path_len * 4) + 4 + 4;
-    buf[proc_id_offset] = 0xFF;
+    let body_len_offset = body_len_offset(&buf);
+    let inflated_body_len = 999u32;
+    buf[body_len_offset..body_len_offset + 4].copy_from_slice(&inflated_body_len.to_le_bytes());
+
     assert_eq!(
         Packet::deserialize(&buf).unwrap_err(),
-        DeserializeError::InvalidUtf8
+        DeserializeError::BodyLengthMismatch
+    );
+}
+
+#[test]
+fn body_too_short_for_procedure_id_is_rejected() {
+    let mut buf = make_packet().serialize().unwrap();
+    let body_len_offset = body_len_offset(&buf);
+    let short_body_len = 3u32;
+    buf[body_len_offset..body_len_offset + 4].copy_from_slice(&short_body_len.to_le_bytes());
+
+    assert_eq!(
+        Packet::deserialize(&buf).unwrap_err(),
+        DeserializeError::BufferTooShort
     );
 }