test(ontology): harden domain/range validation + add missing tests (#848)

Fixes #826. Addresses all five points the maintainer called out in
the follow-up to #825.

Source change (trustgraph-flow/trustgraph/extract/kg/ontology/extract.py):
- Added `_is_subclass_of(cls, target, ontology_subset, max_depth=100)`
  helper with visited-set cycle detection + a defensive depth cap.
  LLM-generated ontologies may emit cycles (A subclass_of B,
  B subclass_of A); the prior while-loop would infinite-loop on that.
- Replaced both near-identical domain and range subclass walks in
  `is_valid_triple` with a single call to the new helper. Net is
  -20 duplicated lines + 26-line helper.

Tests (tests/unit/test_extract/test_ontology/test_prompt_and_extraction.py):
- test_is_valid_triple_subclass_is_accepted: domain expects Recipe,
  actual type is Cake (subclass), validates.
- test_is_valid_triple_handles_subclass_cycle_without_infinite_loop:
  A subclass_of B, B subclass_of A; call returns False within the
  depth cap rather than hanging.
- test_parse_and_validate_triples_collects_entity_types_from_rdf_type:
  end-to-end path: rdf:type triples build the entity_types dict,
  subsequent domain-check triples validate against it.
- test_is_valid_triple_entity_types_none_default: the None default
  path now has explicit coverage.

156 existing tests in tests/unit/test_extract/test_ontology still pass.

tests/unit/test_extract/test_ontology/test_prompt_and_extraction.py

@@ -277,6 +277,60 @@ class TestTripleValidation:
         is_invalid = extractor.is_valid_triple(subject, predicate, object_val, sample_ontology_subset, entity_types_invalid)
         assert not is_invalid, "Invalid range should be rejected"
 
+    def test_is_valid_triple_subclass_is_accepted(self, extractor, sample_ontology_subset):
+        """Domain check passes when actual type is a subclass of expected."""
+        sample_ontology_subset.classes["Cake"] = {
+            "uri": "http://purl.org/ontology/fo/Cake",
+            "type": "owl:Class",
+            "subclass_of": "Recipe",
+        }
+        sample_ontology_subset.object_properties["has_ingredient"] = {
+            "domain": "Recipe",
+            "range": "Ingredient",
+        }
+
+        result = extractor.is_valid_triple(
+            subject="cake:lemon-drizzle",
+            predicate="has_ingredient",
+            object_val="ingredient:lemon",
+            ontology_subset=sample_ontology_subset,
+            entity_types={"cake:lemon-drizzle": "Cake", "ingredient:lemon": "Ingredient"},
+        )
+
+        assert result is True
+
+    def test_is_valid_triple_handles_subclass_cycle_without_infinite_loop(self, extractor, sample_ontology_subset):
+        """A cycle in subclass_of must return False instead of hanging."""
+        sample_ontology_subset.classes["A"] = {"subclass_of": "B"}
+        sample_ontology_subset.classes["B"] = {"subclass_of": "A"}
+        sample_ontology_subset.object_properties["p"] = {"domain": "Recipe", "range": "Ingredient"}
+
+        result = extractor.is_valid_triple(
+            subject="entity:x",
+            predicate="p",
+            object_val="ingredient:y",
+            ontology_subset=sample_ontology_subset,
+            entity_types={"entity:x": "A", "ingredient:y": "Ingredient"},
+        )
+
+        assert result is False
+
+    def test_is_valid_triple_entity_types_none_default(self, extractor, sample_ontology_subset):
+        """entity_types=None should not raise; domain/range checks skip if type unknown."""
+        sample_ontology_subset.object_properties["has_ingredient"] = {
+            "domain": "Recipe",
+            "range": "Ingredient",
+        }
+
+        result = extractor.is_valid_triple(
+            subject="recipe:x",
+            predicate="has_ingredient",
+            object_val="ingredient:y",
+            ontology_subset=sample_ontology_subset,
+        )
+
+        assert result is True
+
 
 class TestTripleParsing:
     """Test suite for parsing triples from LLM responses."""
@@ -377,6 +431,24 @@ class TestTripleParsing:
         assert triple.p.type == IRI, "Predicate should be IRI type"
         assert triple.o.type == LITERAL, "Object literal should be LITERAL type"
 
+    def test_parse_and_validate_triples_collects_entity_types_from_rdf_type(self, extractor, sample_ontology_subset):
+        """entity_types should be built from rdf:type triples in the same batch."""
+        sample_ontology_subset.object_properties["has_ingredient"] = {
+            "domain": "Recipe",
+            "range": "Ingredient",
+        }
+        triples_response = [
+            {"subject": "recipe:cornish-pasty", "predicate": "rdf:type", "object": "Recipe"},
+            {"subject": "ingredient:beef", "predicate": "rdf:type", "object": "Ingredient"},
+            {"subject": "recipe:cornish-pasty", "predicate": "has_ingredient", "object": "ingredient:beef"},
+        ]
+
+        valid_triples = extractor.parse_and_validate_triples(
+            triples_response, sample_ontology_subset
+        )
+
+        assert len(valid_triples) == 3
+
 
 class TestURIExpansionInExtraction:
     """Test suite for URI expansion during triple extraction."""

trustgraph-flow/trustgraph/extract/kg/ontology/extract.py

@@ -540,6 +540,32 @@ class Processor(FlowProcessor):
             return True
         return False
 
+    def _is_subclass_of(self, cls, target, ontology_subset, max_depth=100):
+        """Return True if cls is a subclass of target via subclass_of chain.
+
+        Defends against cycles in ontology data (LLM-generated ontologies may
+        emit A subclass_of B, B subclass_of A) with a visited set. A depth cap
+        acts as a second line of defense against unbounded chains.
+        """
+        if cls == target:
+            return True
+        visited = set()
+        curr = cls
+        depth = 0
+        while curr in ontology_subset.classes and depth < max_depth:
+            if curr in visited:
+                return False  # cycle detected
+            visited.add(curr)
+            cls_def = ontology_subset.classes[curr]
+            parent = cls_def.get('subclass_of') if isinstance(cls_def, dict) else None
+            if parent is None:
+                return False
+            if parent == target:
+                return True
+            curr = parent
+            depth += 1
+        return False
+
     def is_valid_triple(self, subject: str, predicate: str, object_val: str,
                        ontology_subset: OntologySubset, entity_types: dict = None) -> bool:
         """Validate triple against ontology constraints."""
@@ -570,36 +596,20 @@ class Processor(FlowProcessor):
         expected_domain = prop_def.get('domain')
         if expected_domain and subject in entity_types:
             actual_domain = entity_types[subject]
-            if actual_domain != expected_domain:
+            if actual_domain != expected_domain and not self._is_subclass_of(
-                is_subclass = False
+                actual_domain, expected_domain, ontology_subset
-                curr_class = actual_domain
+            ):
-                while curr_class in ontology_subset.classes:
+                return False
-                    cls_def = ontology_subset.classes[curr_class]
-                    parent = cls_def.get('subclass_of') if isinstance(cls_def, dict) else None
-                    if parent == expected_domain:
-                        is_subclass = True
-                        break
-                    curr_class = parent
-                if not is_subclass:
-                    return False
 
         # Range validation
         if is_obj_prop:
             expected_range = prop_def.get('range')
             if expected_range and object_val in entity_types:
                 actual_range = entity_types[object_val]
-                if actual_range != expected_range:
+                if actual_range != expected_range and not self._is_subclass_of(
-                    is_subclass = False
+                    actual_range, expected_range, ontology_subset
-                    curr_class = actual_range
+                ):
-                    while curr_class in ontology_subset.classes:
+                    return False
-                        cls_def = ontology_subset.classes[curr_class]
-                        parent = cls_def.get('subclass_of') if isinstance(cls_def, dict) else None
-                        if parent == expected_range:
-                            is_subclass = True
-                            break
-                        curr_class = parent
-                    if not is_subclass:
-                        return False
 
         return True