fixup! Add snapshot file format with persistence and load

Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>

Author: ludfjig

src/hyperlight_host/src/sandbox/snapshot/file.rs

@@ -640,13 +640,11 @@ impl Snapshot {
     /// The file format uses a page-aligned memory blob that can be
     /// mmapped directly on load for zero-copy instantiation.
     ///
-    /// Note: extra memory regions added via
-    /// [`map_region`](crate::MultiUseSandbox::map_region) or
-    /// [`map_file_cow`](crate::MultiUseSandbox::map_file_cow) are
-    /// **not** persisted. Only the primary sandbox memory is saved.
-    /// Regions that were folded into the snapshot memory (by taking
-    /// a snapshot after mapping) are included since they become part
-    /// of the memory blob.
+    /// # Portability
+    ///
+    /// Snapshot files are **not portable** across CPU architectures,
+    /// hypervisors, or operating systems. All three are checked at
+    /// load time and a mismatch produces an error.
     pub fn to_file(&self, path: impl AsRef<std::path::Path>) -> crate::Result<()> {
         use std::io::{BufWriter, Write};
 
@@ -750,6 +748,10 @@ impl Snapshot {
     /// The memory blob is mapped directly from the file for zero-copy
     /// loading using platform-specific CoW mechanisms.
     ///
+    /// Returns an error if the file is from a different CPU
+    /// architecture, hypervisor, or OS than this host. See
+    /// [`Snapshot::to_file`] for the full portability story.
+    ///
     /// Note: ELF unwind info (`LoadInfo`) is not persisted in the
     /// snapshot file, so the `mem_profile` feature will not have
     /// accurate profiling data for sandboxes created from disk
@@ -761,6 +763,9 @@ impl Snapshot {
     /// Load a snapshot from a file on disk without verifying the
     /// content hash. This is faster for large snapshots in trusted
     /// environments where file integrity is guaranteed by other means.
+    ///
+    /// All other portability checks (architecture, hypervisor, OS)
+    /// still apply. See [`Snapshot::to_file`] for details.
     pub fn from_file_unchecked(path: impl AsRef<std::path::Path>) -> crate::Result<Self> {
         Self::from_file_impl(path, false)
     }