test(core): exhaustive round-trip for all seven ItemCore variants

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/idfoto-core/src/item_types/mod.rs

@@ -73,4 +73,56 @@ mod tests {
         let json = serde_json::to_string(&ItemType::SecureNote).unwrap();
         assert_eq!(json, "\"secure_note\"");
     }
+
+    #[test]
+    fn item_core_login_round_trip_via_tag() {
+        use zeroize::Zeroizing;
+        let core = ItemCore::Login(LoginCore {
+            username: Some("alice".into()),
+            password: Some(Zeroizing::new("hunter2".into())),
+            url: None,
+            totp: None,
+        });
+        let json = serde_json::to_string(&core).unwrap();
+        // Tag-based: outer object has "type": "login"
+        assert!(json.contains("\"type\":\"login\""));
+        let parsed: ItemCore = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed.item_type(), ItemType::Login);
+    }
+
+    #[test]
+    fn item_core_secure_note_round_trip_via_tag() {
+        use zeroize::Zeroizing;
+        let core = ItemCore::SecureNote(SecureNoteCore { body: Zeroizing::new("hello".into()) });
+        let json = serde_json::to_string(&core).unwrap();
+        assert!(json.contains("\"type\":\"secure_note\""));
+        let parsed: ItemCore = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed.item_type(), ItemType::SecureNote);
+    }
+
+    #[test]
+    fn item_core_round_trips_for_all_seven_types() {
+        use zeroize::Zeroizing;
+        use crate::ids::AttachmentId;
+
+        let cores = vec![
+            ItemCore::Login(LoginCore::default()),
+            ItemCore::SecureNote(SecureNoteCore::default()),
+            ItemCore::Identity(IdentityCore::default()),
+            ItemCore::Card(CardCore::default()),
+            ItemCore::Key(KeyCore::default()),
+            ItemCore::Document(DocumentCore {
+                filename: "x".into(),
+                mime_type: "text/plain".into(),
+                primary_attachment: AttachmentId("0123456789abcdef".into()),
+            }),
+            ItemCore::Totp(TotpCore::default()),
+        ];
+        for core in cores {
+            let expected_type = core.item_type();
+            let json = serde_json::to_string(&core).unwrap();
+            let parsed: ItemCore = serde_json::from_str(&json).expect("round-trip failed");
+            assert_eq!(parsed.item_type(), expected_type);
+        }
+    }
 }