Return no historic UPRN for missing, ambiguous, or zero-score matches 🟩

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/repositories/historic_epc/test_historic_epc_resolver.py

@@ -74,3 +74,41 @@ def test_resolve_uprn_returns_unambiguous_match():
     assert uprn == "100"
     assert address == "47 GORDON ROAD"
     assert score > 0
+
+
+def test_resolve_uprn_is_none_when_postcode_has_no_data():
+    # Arrange — valid postcode, but the backup has no shard for it.
+    resolver = HistoricEpcResolver(_FakeRepo({}))
+
+    # Act / Assert
+    assert resolver.resolve_uprn("47 Gordon Road", "AB33 8AL") is None
+
+
+def test_resolve_uprn_is_none_on_ambiguous_tie():
+    # Arrange — two identical addresses with different UPRNs share rank-1.
+    repo = _FakeRepo(
+        {
+            "AB338AL": [
+                _hist("47 GORDON ROAD", "100"),
+                _hist("47 GORDON ROAD", "200"),
+            ]
+        }
+    )
+
+    # Act / Assert
+    assert HistoricEpcResolver(repo).resolve_uprn("47 Gordon Road", "AB33 8AL") is None
+
+
+def test_resolve_uprn_is_none_when_all_scores_zero():
+    # Arrange — no candidate shares the user's building number => all hard-zero.
+    repo = _FakeRepo(
+        {
+            "AB338AL": [
+                _hist("999 ELSEWHERE", "100"),
+                _hist("888 ELSEWHERE", "200"),
+            ]
+        }
+    )
+
+    # Act / Assert
+    assert HistoricEpcResolver(repo).resolve_uprn("47 Gordon Road", "AB33 8AL") is None