feat(modelling): loft overlay 270→300 mm + Elmhurst cascade pin (#1158)

Completes #1158 end-to-end. recommend_loft_insulation now emits a
300 mm overlay (was 270 mm). The Elmhurst before/after re-lodgement of
the loft-insulation measure on cert 001431 lodges the after-cert at
300 mm roof insulation; pinning before→overlay→after requires the
overlay to match that depth — at 270 mm the cascade left a +0.173 SAP
residual, at 300 mm it closes at delta 0.000000 on SAP/CO2/PE.

Adds test_loft_overlay_reproduces_the_relodged_after and updates the
roof generator unit test's thickness assertion to 300.

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

domain/modelling/roof_recommendation.py

@@ -20,8 +20,10 @@ from repositories.product.product_repository import ProductRepository
 _LOFT_MEASURE_TYPE = "loft_insulation"
 # RdSAP 10 Table 16: 0 mm lodged roof insulation is an uninsulated loft.
 _ROOF_UNINSULATED_MM = 0
-# Recommended loft-insulation depth (mm) — the building-regs standard top-up.
-_RECOMMENDED_LOFT_THICKNESS_MM = 270
+# Recommended loft-insulation depth (mm). Elmhurst re-lodges a loft-insulation
+# measure at 300 mm; pinning the before→after cascade (000490/001431) requires
+# the overlay to match that depth exactly (see test_elmhurst_cascade_pins).
+_RECOMMENDED_LOFT_THICKNESS_MM = 300
 
 
 def recommend_loft_insulation(

tests/domain/modelling/test_elmhurst_cascade_pins.py

@@ -20,6 +20,7 @@ from datatypes.epc.domain.epc_property_data import EpcPropertyData
 from domain.modelling.package_scorer import PackageScorer, Score
 from domain.modelling.product import Product
 from domain.modelling.recommendation import Recommendation
+from domain.modelling.roof_recommendation import recommend_loft_insulation
 from domain.modelling.simulation import EpcSimulation
 from domain.modelling.wall_recommendation import recommend_cavity_wall
 from domain.sap10_calculator.calculator import Sap10Calculator, SapResult
@@ -79,3 +80,22 @@ def test_cavity_wall_overlay_reproduces_the_relodged_after() -> None:
     _assert_overlay_reproduces_after(
         before, after, recommendation.options[0].overlay
     )
+
+
+def test_loft_overlay_reproduces_the_relodged_after() -> None:
+    # Arrange
+    before: EpcPropertyData = parse_recommendation_summary(
+        "loft_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "loft_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_loft_insulation(
+        before, _AnyProduct()
+    )
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )

tests/domain/modelling/test_roof_recommendation.py

@@ -46,7 +46,7 @@ def test_uninsulated_loft_yields_a_loft_insulation_recommendation() -> None:
     option = recommendation.options[0]
     assert option.measure_type == "loft_insulation"
     simulated: EpcPropertyData = apply_simulations(baseline, [option.overlay])
-    assert _part(simulated, BuildingPartIdentifier.MAIN).roof_insulation_thickness == 270
+    assert _part(simulated, BuildingPartIdentifier.MAIN).roof_insulation_thickness == 300
 
 
 def test_already_insulated_loft_yields_no_recommendation() -> None: