domain: add cross-cutting value objects (SystemId, DateTimeStamp, Checksum, StructuredData)

crates/domain/tests/value_objects/structured_data.rs

@@ -0,0 +1,45 @@
+use domain::value_objects::{MetadataValue, StructuredData};
+
+#[test]
+fn insert_and_get() {
+    let mut sd = StructuredData::new();
+    sd.insert("key", MetadataValue::String("value".into()));
+    assert_eq!(sd.get_string("key"), Some("value"));
+    assert_eq!(sd.len(), 1);
+    assert!(!sd.is_empty());
+}
+
+#[test]
+fn merge_from_overwrites() {
+    let mut a = StructuredData::new();
+    a.insert("k", MetadataValue::Integer(1));
+
+    let mut b = StructuredData::new();
+    b.insert("k", MetadataValue::Integer(2));
+
+    a.merge_from(b);
+    assert!(matches!(a.get("k"), Some(MetadataValue::Integer(2))));
+}
+
+#[test]
+fn serde_roundtrip() {
+    let mut sd = StructuredData::new();
+    sd.insert("s", MetadataValue::String("hello".into()));
+    sd.insert("i", MetadataValue::Integer(42));
+    sd.insert("f", MetadataValue::Float(3.14));
+    sd.insert("b", MetadataValue::Boolean(true));
+    sd.insert("n", MetadataValue::Null);
+
+    let json = serde_json::to_string(&sd).unwrap();
+    let back: StructuredData = serde_json::from_str(&json).unwrap();
+    assert_eq!(sd, back);
+}
+
+#[test]
+fn remove_works() {
+    let mut sd = StructuredData::new();
+    sd.insert("k", MetadataValue::Integer(1));
+    let removed = sd.remove("k");
+    assert!(matches!(removed, Some(MetadataValue::Integer(1))));
+    assert!(sd.is_empty());
+}