Treatable old-band solid walls keep their EWI and IWI options under the gate 🟩

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/domain/modelling/test_wall_recommendation.py

@@ -130,6 +130,29 @@ def test_at_regs_age_band_wall_yields_no_solid_wall_recommendation() -> None:
     assert recommendation is None
 
 
+def test_treatable_old_band_solid_wall_keeps_its_insulation_options() -> None:
+    # Arrange — solid brick as-built at age band B: the cascade U (~2.1) far
+    # exceeds what 100 mm EWI/IWI achieves, so the Wall U-Value Gate must let
+    # both Options through unchanged (the gate is physical possibility only —
+    # ADR-0051).
+    baseline: EpcPropertyData = build_epc()  # age band B
+    main: SapBuildingPart = _part(baseline, BuildingPartIdentifier.MAIN)
+    main.wall_construction = 3  # solid brick — EWI + IWI constructable
+    main.wall_insulation_type = 4
+
+    # Act
+    recommendation: Recommendation | None = recommend_solid_wall(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is not None
+    assert {option.measure_type for option in recommendation.options} == {
+        "external_wall_insulation",
+        "internal_wall_insulation",
+    }
+
+
 def test_park_home_wall_yields_no_solid_wall_recommendation() -> None:
     # Arrange — a park home (wall_construction code 8) with an uninsulated
     # as-built wall. Code 8 is NOT system-built (ADR-0019); a park home's