diff --git a/crates/ailang-core/src/hash.rs b/crates/ailang-core/src/hash.rs
index 403daba..3001255 100644
--- a/crates/ailang-core/src/hash.rs
+++ b/crates/ailang-core/src/hash.rs
@@ -267,4 +267,70 @@ mod tests {
             "Type::Forall serialised must omit `constraints` when empty; got: {s}"
         );
     }
+
+    /// Iter ct.4 (canonical-type-names milestone close): pin the
+    /// canonical-form hashes of the two cross-module fixtures
+    /// migrated by `ail migrate-canonical-types` in ct.1. These
+    /// hashes are the post-migration state; pre-migration values
+    /// (when both fixtures carried bare cross-module Type::Con)
+    /// are no longer reproducible because the ct.1 validator
+    /// rejects that shape upstream.
+    #[test]
+    fn ct4_migrated_fixtures_have_canonical_form_hashes() {
+        let manifest_dir = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+        let examples = manifest_dir.join("../../examples");
+
+        let ord_src = std::fs::read(examples.join("ordering_match.ail.json"))
+            .expect("examples/ordering_match.ail.json present");
+        let ord_mod: crate::ast::Module = serde_json::from_slice(&ord_src).unwrap();
+        let main_def = ord_mod.defs.iter().find(|d| d.name() == "main").unwrap();
+        assert_eq!(
+            def_hash(main_def),
+            "8d17235aa3d2e127",
+            "ordering_match::main canonical hash must match captured post-migration value"
+        );
+
+        let dup_a_src = std::fs::read(examples.join("test_22b1_dup_a.ail.json"))
+            .expect("examples/test_22b1_dup_a.ail.json present");
+        let dup_a_mod: crate::ast::Module = serde_json::from_slice(&dup_a_src).unwrap();
+        // test_22b1_dup_a has two defs: the Show class and an instance
+        // of Show for test_22b1_dup_b.MyInt. Def::name() returns the
+        // class name for both, so pin each by index. The instance
+        // carries the migrated cross-module qualifier in its `type`.
+        assert_eq!(dup_a_mod.defs.len(), 2, "test_22b1_dup_a expected to have exactly 2 defs (class + instance)");
+        assert_eq!(
+            def_hash(&dup_a_mod.defs[0]),
+            "1c2573661ffd3da3",
+            "test_22b1_dup_a class Show canonical hash must match captured post-migration value"
+        );
+        assert_eq!(
+            def_hash(&dup_a_mod.defs[1]),
+            "cc8685f92f246e40",
+            "test_22b1_dup_a instance Show for test_22b1_dup_b.MyInt canonical hash must match captured post-migration value"
+        );
+    }
+
+    /// Iter ct.4: re-assert that the canonical-form tightening
+    /// did NOT change hashes of intra-module-only fixtures. The
+    /// existing iter-13a / iter-19b / iter-22b.1 pin tests already
+    /// assert these; this one names the canonical-type-names
+    /// milestone explicitly so future archaeology finds the
+    /// connection.
+    #[test]
+    fn ct4_unmigrated_fixtures_remain_bit_identical() {
+        let manifest_dir = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+        let examples = manifest_dir.join("../../examples");
+
+        let sum_src = std::fs::read(examples.join("sum.ail.json")).unwrap();
+        let sum_mod: crate::ast::Module = serde_json::from_slice(&sum_src).unwrap();
+        let sum_def = sum_mod.defs.iter().find(|d| d.name() == "sum").unwrap();
+        assert_eq!(def_hash(sum_def), "db33f57cb329935e",
+            "sum.sum hash drifted across canonical-form tightening — unexpected");
+
+        let list_src = std::fs::read(examples.join("list.ail.json")).unwrap();
+        let list_mod: crate::ast::Module = serde_json::from_slice(&list_src).unwrap();
+        let int_list_def = list_mod.defs.iter().find(|d| d.name() == "IntList").unwrap();
+        assert_eq!(def_hash(int_list_def), "b082192bd0c99202",
+            "list.IntList hash drifted across canonical-form tightening — unexpected");
+    }
 }