feat(modelling): floor insulation-type overlay field + cascade pins (#1159)

Completes #1159 end-to-end with solid and suspended-floor before/after
cascade pins on cert 001431, both closing at delta 0.000000.

Adds floor_insulation_type_str to BuildingPartOverlay (the generic
field-fold applicator picks it up with no change) and has
recommend_floor_insulation set it to "Retro-fitted". Insulating an
as-built floor re-lodges its insulation as retro-fitted; the calculator
keys on this for a suspended timber floor's sealed/unsealed
determination (cert_to_inputs.py: "retro" + no U-value supplied →
sealed). Without it the suspended-floor cascade left a +1.40 SAP gap
(the floor stayed "unsealed", wrong U-value); with it the cascade
closes exactly. Solid floors are unaffected by the seal logic and stay
at delta 0; both Elmhurst after-certs lodge "Retro-fitted", so setting
it uniformly is faithful.

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

domain/modelling/floor_recommendation.py

@@ -21,6 +21,12 @@ from repositories.product.product_repository import ProductRepository
 
 # Recommended ground-floor insulation depth (mm).
 _RECOMMENDED_FLOOR_THICKNESS_MM = 100
+# Insulating an as-built floor re-lodges its insulation as retro-fitted. The
+# calculator keys on this for a suspended timber floor's sealed/unsealed
+# determination (cert_to_inputs: "retro" + no U-value → sealed), so the
+# overlay must set it or the suspended-floor cascade leaves a ~1.4 SAP gap
+# (see test_elmhurst_cascade_pins).
+_RETROFITTED_INSULATION = "Retro-fitted"
 
 
 def _is_uninsulated(thickness: Optional[Union[str, int]]) -> bool:
@@ -75,7 +81,8 @@ def recommend_floor_insulation(
         overlay=EpcSimulation(
             building_parts={
                 BuildingPartIdentifier.MAIN: BuildingPartOverlay(
-                    floor_insulation_thickness=_RECOMMENDED_FLOOR_THICKNESS_MM
+                    floor_insulation_thickness=_RECOMMENDED_FLOOR_THICKNESS_MM,
+                    floor_insulation_type_str=_RETROFITTED_INSULATION,
                 )
             }
         ),

domain/modelling/simulation.py

@@ -24,6 +24,7 @@ class BuildingPartOverlay:
     wall_insulation_type: Optional[int] = None
     roof_insulation_thickness: Optional[int] = None
     floor_insulation_thickness: Optional[int] = None
+    floor_insulation_type_str: Optional[str] = None
 
 
 def _no_building_parts() -> dict[BuildingPartIdentifier, BuildingPartOverlay]:

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.floor_recommendation import recommend_floor_insulation
 from domain.modelling.roof_recommendation import recommend_loft_insulation
 from domain.modelling.simulation import EpcSimulation
 from domain.modelling.wall_recommendation import recommend_cavity_wall
@@ -99,3 +100,41 @@ def test_loft_overlay_reproduces_the_relodged_after() -> None:
     _assert_overlay_reproduces_after(
         before, after, recommendation.options[0].overlay
     )
+
+
+def test_solid_floor_overlay_reproduces_the_relodged_after() -> None:
+    # Arrange
+    before: EpcPropertyData = parse_recommendation_summary(
+        "solid_floor_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "solid_floor_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        before, _AnyProduct()
+    )
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )
+
+
+def test_suspended_floor_overlay_reproduces_the_relodged_after() -> None:
+    # Arrange
+    before: EpcPropertyData = parse_recommendation_summary(
+        "suspended_floor_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "suspended_floor_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        before, _AnyProduct()
+    )
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )