fix: resolve latest review findings

Category quiz creation counts extra-linked questions; primary category is validated on edit; statistics dedupe collapses case variants. 60 backend tests pass.

backend/app/routers/question_categories.py

@@ -8,7 +8,7 @@ from app.database import get_db
 from app.models.question import Question
 from app.models.question_category import QuestionCategory, QuestionCategoryLink
 from app.models.user import User
-from app.services.quiz_builder import (bank_query, category_descendants, category_breadcrumbs,
+from app.services.quiz_builder import (bank_query, filtered_bank_query, category_descendants, category_breadcrumbs,
     validate_parent, GenerateTestRequest, generate_test)
 from app.utils.auth import get_current_user, require_moderator
 
@@ -107,11 +107,13 @@ def create_quiz_from_question_category(cat_id: int, title: str, mode: str = "tim
     time_limit_minutes: int | None = None, count: int | None = None,
     db: Session = Depends(get_db), current_user: User = Depends(get_current_user)):
     ids = category_descendants(db.query(QuestionCategory).all(), [cat_id])
-    available = bank_query(db, current_user).filter(Question.question_category_id.in_(ids)).count()
+    available = filtered_bank_query(db, current_user, [cat_id]).count()
     if mode not in ("timed", "learning") or not title.strip() or len(title) > 200 or (time_limit_minutes is not None and time_limit_minutes <= 0):
         raise HTTPException(400, "Provide a title, valid mode, and positive time limit")
+    if available == 0:
+        raise HTTPException(400, "No available questions in this category")
     count = available if count is None else count
-    if not 1 <= count <= 200:
-        raise HTTPException(400, "Select between 1 and 200 available questions using Create Custom Test")
+    if not 1 <= count <= min(200, available):
+        raise HTTPException(400, "Select between 1 and the available questions using Create Custom Test")
     return generate_test(db, current_user, GenerateTestRequest(title=title, mode=mode,
         time_limit_minutes=time_limit_minutes, count=count, category_ids=[cat_id]))

backend/app/routers/questions.py

@@ -89,6 +89,8 @@ def edit_question(
     if question.user_id != current_user.id and not is_mod:
         raise HTTPException(status_code=403, detail="Not authorized to edit this question")
     values = validate_image_attachments(db, current_user, data.model_dump(exclude_unset=True))
+    if values.get("question_category_id") is not None and not db.get(QuestionCategory, values["question_category_id"]):
+        raise HTTPException(400, "Category not found")
     explanations = values.pop("option_explanations", None)
     if explanations is not None:
         values["option_explanations"] = validate_option_explanations(

backend/app/routers/study_tools.py

@@ -227,9 +227,9 @@ def question_responses(attempt_id: int, question_id: int, db: Session = Depends(
     for answer, count in rows:
         if answer and answer.strip():
             counts[answer.strip().casefold()] += count
-    # Duplicate option strings must not double-count the same answer.
-    options = list(dict.fromkeys(question.options or []))
-    stats = [{"option": option, "count": counts[option.strip().casefold()]} for option in options]
+    # Duplicate option strings must not double-count the same answer; case variants collapse too.
+    options = list(dict.fromkeys((option.casefold() for option in (question.options or []))))
+    stats = [{"option": option, "count": counts[option.casefold()]} for option in options]
     sample_size = sum(option["count"] for option in stats)
     for option in stats:
         option["percentage"] = round(100 * option["count"] / sample_size, 1) if sample_size else 0

backend/tests/test_multi_category.py

@@ -39,6 +39,9 @@ class MultiCategoryTests(unittest.TestCase):
         self.assertEqual([row['id'] for row in bank['questions']], [3])
         self.assertEqual(set(bank['questions'][0]['category_ids']), {2, 3, 4})
         self.assertEqual(self.client.get('/questions/bank/ids', params={'category_ids': '4'}).json(), [3])
+        # Category quiz creation counts extra-linked questions too.
+        created = self.client.post('/question-categories/4/create-quiz', params={'title': 'Linked quiz', 'mode': 'learning'})
+        self.assertEqual(created.status_code, 200, created.text)
         # Peers cannot see the private question through the shared category.
         self.bank.user = self.bank.peer
         self.assertEqual(self.client.get('/questions/builder/count', params={'category_ids': [4]}).json()['count'], 0)
@@ -46,6 +49,7 @@ class MultiCategoryTests(unittest.TestCase):
     def test_additional_categories_replace_validate_and_ignore_primary(self):
         self.bank.user = self.bank.owner
         self.assertEqual(self.client.patch('/questions/3', json={'additional_category_ids': [999]}).status_code, 400)
+        self.assertEqual(self.client.patch('/questions/3', json={'question_category_id': 999}).status_code, 400)
         self.assertEqual(self.client.patch('/questions/3', json={'additional_category_ids': [3, 4, 4]}).status_code, 200)
         links = {link.category_id for link in self.bank.db.query(QuestionCategoryLink).filter_by(question_id=3)}
         self.assertEqual(links, {4})  # Primary is ignored; duplicates collapsed.

backend/tests/test_study_tools.py

@@ -126,9 +126,9 @@ class StudyToolTests(unittest.TestCase):
         self.assertEqual(response['sample_size'], 1)
         self.assertEqual([row['count'] for row in response['options']], [1, 0])
         self.assertEqual(response['options'][0]['percentage'], 100.0)
-        # Duplicate option strings must not double-count.
+        # Duplicate option strings must not double-count; case variants collapse too.
         question = self.bank.db.get(fixtures.Question, 1)
-        question.options = ['yes', 'yes']
+        question.options = ['yes', 'YES']
         self.bank.db.commit()
         response = self.client.get(f'/study-tools/attempts/{study}/questions/1/responses').json()
         self.assertEqual(response['sample_size'], 1)