test: enforce research integrity contracts

tests/test_refusal_detection.py

@@ -132,8 +132,12 @@ class TestRefusalRateWithCI:
 
     def test_empty_responses(self):
         ci = refusal_rate_with_ci([], mode="combined")
-        assert ci["rate"] == 0.0
+        assert ci["available"] is False
+        assert ci["rate"] is None
+        assert ci["ci_lower"] is None
+        assert ci["ci_upper"] is None
         assert ci["n_samples"] == 0
+        assert ci["refusal_count"] == 0
 
     def test_ci_narrower_with_more_samples(self):
         """More samples should produce tighter confidence intervals."""