feat: add external byte codecs

CHANGELOG.md

@@ -14,6 +14,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   identical and its digest is unchanged, so this is transparent to readers and
   to previously saved snapshots. Filesystems that do not support sparse files
   store the blob as before.
+* Expose C guest `ByteChunks` values as pointer and length arrays.
+* Return typed `hl_ReturnValue` objects from C guest functions through
+  `hl_result_from_*` constructors.
 
 ### Removed
 

src/hyperlight_common/src/flatbuffer_wrappers/codec.rs

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright 2026 The Hyperlight Authors.
+
+use alloc::vec::Vec;
+
+use anyhow::Result;
+use bytes::Bytes;
+
+/// Receives external byte values while their FlatBuffer metadata is encoded.
+///
+/// Values are delivered in their logical order without flattening chunked
+/// values. The value lifetime allows a sink to retain references until the
+/// control buffer has been written, without copying payload bytes.
+pub trait ExternalValueSink<'a> {
+    /// Receive one contiguous byte value.
+    fn push_bytes(&mut self, value: &'a [u8]) -> Result<()>;
+
+    /// Receive one logical byte sequence represented as chunks.
+    fn push_chunks(&mut self, value: &'a [Bytes]) -> Result<()>;
+}
+
+/// Supplies complete external byte values while a FlatBuffer is decoded.
+///
+/// Implementations must validate `length` against available input and the
+/// resource budget before allocating.
+pub trait ExternalValueSource {
+    /// Take the next external value as contiguous bytes.
+    fn take_bytes(&mut self, length: usize) -> Result<Vec<u8>>;
+
+    /// Take the next external value as owned byte chunks.
+    fn take_chunks(&mut self, length: usize) -> Result<Vec<Bytes>>;
+
+    /// Finish decoding and reject any unused external values.
+    fn finish(&mut self) -> Result<()>;
+}