fix: surface IndexError from conversion and pin the response shape

serialize_object() swallows IndexError alongside ValueError and TypeError
into a 404, so an IndexError raised during conversion would report a
corrupt row as a missing one - the failure mode consolidate()'s re-raise
exists to prevent. Widen the caught tuple to match.

Assert the node language the values tuple carries for the conversion does
not leak into the response, on both the converted and passed-through
branches; without the latter a pop placed after the passthrough check
would ship an internal join key to the client.

Correct the comment on the answerless item body: an empty <div /> inside
qti-item-body is XSD-valid, so the empty <p /> is there to give the body
a paragraph to render and edit, not to satisfy the schema.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: rtibblesbot

contentcuration/contentcuration/tests/utils/qti/test_convert.py

@@ -156,8 +156,8 @@ def test_choice_types_with_no_answers_omit_the_interaction(self):
                 self.assertTrue(validate_qti_item(result.xml.encode("utf-8")).is_valid)
 
     def test_choice_type_with_no_answers_and_no_question(self):
-        # The model's own defaults, and qti-item-body cannot be empty - so a
-        # question with nothing typed into it yet carries an empty paragraph.
+        # The model's own defaults - a question with nothing typed into it yet
+        # still carries an empty paragraph to render and edit.
         item = _make_item(
             type=exercises.MULTIPLE_SELECTION,
             question="",

contentcuration/contentcuration/tests/viewsets/test_assessmentitem.py

@@ -1265,6 +1265,8 @@ def test_converted_item_has_no_legacy_field_content(self):
         self.assertEqual(item["question"], "")
         self.assertEqual(item["answers"], "[]")
         self.assertEqual(item["hints"], "[]")
+        # The node language is only in the values tuple to feed the conversion.
+        self.assertNotIn("contentnode__language__lang_code", item)
 
     def test_converted_items_are_tagged_with_their_own_node_language(self):
         # A contentnode__in read spans several nodes, so each item has to pick
@@ -1321,6 +1323,8 @@ def test_perseus_question_returned_unchanged(self):
 
         self.assertEqual(item["type"], exercises.PERSEUS_QUESTION)
         self.assertEqual(item["raw_data"], raw_data)
+        # A passed-through row must shed the node language too.
+        self.assertNotIn("contentnode__language__lang_code", item)
 
     def test_native_qti_item_returned_unchanged(self):
         assessment_id = self._create_item(

contentcuration/contentcuration/utils/assessment/qti/convert.py

@@ -325,8 +325,9 @@ def convert_legacy_assessment_item_to_qti(
     if interaction is None:
         # Emit the question text alone, ungraded. Div because rendered markdown
         # can start with a top level <math>, which qti-item-body does not accept
-        # directly; P() because the container cannot be empty and a newly added
-        # question has no text yet.
+        # directly; the empty P stands in for the text a newly added question
+        # does not have yet, so the body is a paragraph to render and edit
+        # rather than a bare empty div.
         item_body = ItemBody(
             children=[
                 Div(children=_create_html_content_from_text(item.question) or [P()])

contentcuration/contentcuration/viewsets/assessmentitem.py

@@ -360,11 +360,11 @@ def consolidate(self, items, queryset):
             try:
                 # A new dict, so the language does not leak into the response.
                 result = convert_legacy_question_to_qti(dict(item, language=language))
-            except (ValueError, TypeError) as e:
-                # serialize_object() turns ValueError/TypeError into a 404
-                # (base.py), reporting a corrupt row as a missing one; re-raise
-                # as a type it does not catch (pydantic and json errors both
-                # subclass ValueError).
+            except (IndexError, ValueError, TypeError) as e:
+                # serialize_object() turns IndexError/ValueError/TypeError into
+                # a 404 (base.py), reporting a corrupt row as a missing one;
+                # re-raise as a type it does not catch (pydantic and json errors
+                # both subclass ValueError).
                 raise LegacyConversionError(
                     f"Could not convert assessment item {item['assessment_id']} to QTI"
                 ) from e