fix(lobby): avoid orphaned round configs on round start

lobby/tests.py

@@ -308,6 +308,23 @@ class StartRoundTests(TestCase):
         self.assertEqual(response.json()["locale"], "en")
         self.assertEqual(response.json()["error"], "Only host can start round")
 
+    @patch("lobby.views._select_round_question", side_effect=ValueError("no_available_questions"))
+    def test_start_round_does_not_persist_round_config_when_question_selection_fails(self, _mock_select_round_question):
+        self.client.login(username="host", password="secret123")
+
+        response = self.client.post(
+            reverse("lobby:start_round", kwargs={"code": self.session.code}),
+            data={"category_slug": self.category.slug},
+            content_type="application/json",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json()["error_code"], "no_available_questions")
+        self.session.refresh_from_db()
+        self.assertEqual(self.session.status, GameSession.Status.LOBBY)
+        self.assertFalse(RoundConfig.objects.filter(session=self.session, number=1).exists())
+        self.assertFalse(RoundQuestion.objects.filter(session=self.session, round_number=1).exists())
+
 
 class LieSubmissionTests(TestCase):
     def setUp(self):
@@ -1329,6 +1346,26 @@ class RevealRoundFlowTests(TestCase):
         self.assertEqual(response.json()["locale"], "da")
         self.assertEqual(response.json()["error"], "Næste runde kan kun starte fra scoreboard-fasen")
 
+    def test_start_next_round_does_not_persist_round_config_when_question_selection_fails(self):
+        self.client.login(username="host_reveal", password="secret123")
+        self.client.get(reverse("lobby:reveal_scoreboard", kwargs={"code": self.session.code}))
+        self.next_question.delete()
+
+        response = self.client.post(
+            reverse(
+                "lobby:start_next_round",
+                kwargs={"code": self.session.code},
+            )
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json()["error_code"], "no_available_questions")
+        self.session.refresh_from_db()
+        self.assertEqual(self.session.status, GameSession.Status.SCOREBOARD)
+        self.assertEqual(self.session.current_round, 1)
+        self.assertFalse(RoundConfig.objects.filter(session=self.session, number=2).exists())
+        self.assertFalse(RoundQuestion.objects.filter(session=self.session, round_number=2).exists())
+
     def test_reveal_scoreboard_unsupported_locale_falls_back_to_en_deterministically(self):
         self.client.login(username="other_reveal", password="secret123")