Seed optional history values from explicit constructors

crates/oa-desktop/src/forms/history_fields.rs

@@ -120,7 +120,9 @@ fn seed(schema: &'static Value, depth: usize) -> Result<Value, &'static str> {
     if let Some(options) = alternatives(schema) {
         if options
             .iter()
-            .any(|s| matches_value(s, &json!("NotApplicable"), 0))
+            .filter_map(|s| resolve(s).ok())
+            .filter_map(|s| s.get("enum").and_then(Value::as_array))
+            .any(|values| values.contains(&json!("NotApplicable")))
         {
             return Ok(json!("NotApplicable"));
         }

crates/oa-desktop/src/forms/history_fields/tests.rs

@@ -752,6 +752,38 @@ fn choose_history_constructor(draft: &mut Draft, path: &str, label: &str) {
     draft.shape(&path, value).unwrap();
 }
 
+#[test]
+fn history_optional_uuid_and_text_seed_absence_without_inventing_observations() {
+    for fact in ["Header/Parent", "Artifact/review/Revision"] {
+        let side = format!("{FACETS}/0/{fact}/oa");
+        let schema = resolve(schema_at(&side).unwrap()).unwrap();
+        assert_eq!(seed(schema, 0).unwrap(), json!("NotApplicable"));
+        let observed_value = alternatives(schema)
+            .unwrap()
+            .iter()
+            .find(|branch| branch_label(branch) == "Observed value")
+            .unwrap();
+        let value = branch_seed(observed_value).unwrap();
+        assert_eq!(value, json!({"Value": null}));
+        assert_eq!(
+            seed(schema_at(&format!("{side}/Value")).unwrap(), 0).unwrap(),
+            Value::Null,
+            "a plain text/UUID shape is not the NotApplicable enum constructor"
+        );
+        if fact == "Header/Parent" {
+            assert_eq!(
+                serde_json::from_value::<Observed<Option<Id>>>(value).unwrap(),
+                Observed::Value(None)
+            );
+        } else {
+            assert_eq!(
+                serde_json::from_value::<Observed<Option<String>>>(value).unwrap(),
+                Observed::Value(None)
+            );
+        }
+    }
+}
+
 #[test]
 fn history_nested_optional_number_events_switch_absent_present_and_recover_invalid_raw() {
     let (project, id) = fixture(Some(baseline(vec![])));