diff --git a/crates/jacquard-codegen-tests/src/lib.rs b/crates/jacquard-codegen-tests/src/lib.rs
index 5077c1bc4..6bb34f926 100644
--- a/crates/jacquard-codegen-tests/src/lib.rs
+++ b/crates/jacquard-codegen-tests/src/lib.rs
@@ -108,6 +108,38 @@ mod tests {
         let _: Option<super::pretty::test_ns3::collision::Foo> = None;
     }
 
+    #[test]
+    fn generated_record_dag_cbor_roundtrip_is_byte_stable() {
+        use jacquard_common::{DefaultStr, deps::smol_str::SmolStr};
+
+        type Record = super::pretty::test_collision::collection::CollectionRecord<DefaultStr>;
+        let record = Record {
+            created_at: None,
+            items: vec![super::pretty::test_collision::collection::Collection {
+                count: None,
+                label: SmolStr::new("nested"),
+                extra_data: None,
+            }],
+            name: SmolStr::new("test"),
+            extra_data: None,
+        };
+        let bytes = serde_ipld_dagcbor::to_vec(&record).expect("serialize generated record");
+        let decoded: Record =
+            serde_ipld_dagcbor::from_slice(&bytes).expect("deserialize generated record");
+        let reencoded =
+            serde_ipld_dagcbor::to_vec(&decoded).expect("re-serialize generated record");
+
+        assert_eq!(
+            decoded.extra_data, None,
+            "$type must not leak into extra_data"
+        );
+        assert_eq!(
+            decoded.items[0].extra_data, None,
+            "empty object extra_data must remain None"
+        );
+        assert_eq!(reencoded, bytes, "generated record encoding must be stable");
+    }
+
     // -- Macro mode type accessibility (same types, different module root) --
 
     #[test]
diff --git a/crates/jacquard-lexicon/src/codegen/structs.rs b/crates/jacquard-lexicon/src/codegen/structs.rs
index 332457214..643c20071 100644
--- a/crates/jacquard-lexicon/src/codegen/structs.rs
+++ b/crates/jacquard-lexicon/src/codegen/structs.rs
@@ -139,6 +139,10 @@ impl<'c> CodeGenerator<'c> {
                 let is_none_path = resolved.option_is_none_path();
                 let extra_data_type =
                     resolved.option_type(quote! { #btree_map<#smolstr_type, #data_type> });
+                let deserialize_extra_data_name =
+                    format!("deserialize_{}_extra_data", type_name.to_snake_case());
+                let deserialize_extra_data =
+                    syn::Ident::new(&deserialize_extra_data_name, proc_macro2::Span::call_site());
                 let struct_def = quote! {
                     #doc
                     #derive_attr
@@ -147,10 +151,35 @@ impl<'c> CodeGenerator<'c> {
                     ))]
                     pub struct #ident<S: #bosstr_path = #default_str_path> {
                         #fields
-                        #[serde(flatten, default, skip_serializing_if = #is_none_path)]
+                        #[serde(
+                            flatten,
+                            default,
+                            deserialize_with = #deserialize_extra_data_name,
+                            skip_serializing_if = #is_none_path
+                        )]
                         pub extra_data: #extra_data_type,
                     }
                 };
+                let extra_data_deserializer = quote! {
+                    fn #deserialize_extra_data<'de, S, D>(
+                        deserializer: D,
+                    ) -> Result<#extra_data_type, D::Error>
+                    where
+                        S: #bosstr_path + serde::Deserialize<'de>,
+                        D: serde::Deserializer<'de>,
+                    {
+                        let mut data = <#extra_data_type as serde::Deserialize<'de>>::deserialize(
+                            deserializer,
+                        )?;
+                        if let Some(extra_data) = &mut data {
+                            extra_data.remove("$type");
+                            if extra_data.is_empty() {
+                                data = None;
+                            }
+                        }
+                        Ok(data)
+                    }
+                };
 
                 // Generate custom builder if needed.
                 let builder = if has_builder {
@@ -281,6 +310,7 @@ impl<'c> CodeGenerator<'c> {
                 };
 
                 let internals = quote! {
+                    #extra_data_deserializer
                     #(#default_fns)*
                     #manual_default
                     #nested_internals
@@ -349,16 +379,37 @@ impl<'c> CodeGenerator<'c> {
         let is_none_path = resolved.option_is_none_path();
         let extra_data_type =
             resolved.option_type(quote! { #btree_map<#smolstr_type, #data_type> });
+        let deserialize_extra_data_name =
+            format!("deserialize_{}_extra_data", type_name.to_snake_case());
+        let deserialize_extra_data =
+            syn::Ident::new(&deserialize_extra_data_name, proc_macro2::Span::call_site());
         let struct_def = quote! {
             #doc
             #derive_attr
             #[serde(rename_all = "camelCase", bound(deserialize = #serde_de_bound))]
             pub struct #ident<S: #bosstr_path = #default_str_path> {
                 #fields
-                #[serde(flatten, default, skip_serializing_if = #is_none_path)]
+                #[serde(
+                    flatten,
+                    default,
+                    deserialize_with = #deserialize_extra_data_name,
+                    skip_serializing_if = #is_none_path
+                )]
                 pub extra_data: #extra_data_type,
             }
         };
+        let extra_data_deserializer = quote! {
+            fn #deserialize_extra_data<'de, S, D>(
+                deserializer: D,
+            ) -> Result<#extra_data_type, D::Error>
+            where
+                S: #bosstr_path + serde::Deserialize<'de>,
+                D: serde::Deserializer<'de>,
+            {
+                let data = <#extra_data_type as serde::Deserialize<'de>>::deserialize(deserializer)?;
+                Ok(data.filter(|extra_data| !extra_data.is_empty()))
+            }
+        };
 
         // Generate custom builder if needed.
         let builder = if has_builder {
@@ -400,6 +451,7 @@ impl<'c> CodeGenerator<'c> {
         };
 
         let internals = quote! {
+            #extra_data_deserializer
             #(#default_fns)*
             #manual_default
             #nested_internals