feat(modelling): ASHP option carries the composite per-dwelling cost

Slice 9 of ADR-0025 costing. _ashp_option now prices via Products.ashp_bundle_
cost(ashp_cost_inputs(epc)) instead of the flat catalogue scalar; the catalogue
row is still read for its material_id. Pinned on boiler-3: gas reuse dwelling
composes to 15600.60 (decommission 720 + pump 9720 + cylinder 2382.60 + reuse
distribution 2778) with 25% contingency.

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

domain/modelling/generators/heating_recommendation.py

@@ -17,7 +17,7 @@ from typing import Optional
 from datatypes.epc.domain.epc_property_data import EpcPropertyData, MainHeatingDetail
 from datatypes.epc.domain.field_mappings import PROPERTY_TYPE_LOOKUP
 from domain.geospatial.planning_restrictions import PlanningRestrictions
-from domain.modelling.products import AshpCostInputs, AshpExistingSystem
+from domain.modelling.products import AshpCostInputs, AshpExistingSystem, Products
 from domain.modelling.recommendation import Cost, MeasureOption, Recommendation
 from domain.modelling.simulation import EpcSimulation, HeatingOverlay
 from repositories.product.product_repository import ProductRepository
@@ -214,7 +214,10 @@ def _ashp_option(
     that is not listed/heritage and not already a heat pump."""
     if not _ashp_eligible(epc, restrictions):
         return None
+    # Cost is composed per-dwelling from the rate sheet (ADR-0025), not the
+    # single catalogue scalar; the catalogue row is still read for its id.
     product = products.get(_ASHP_MEASURE_TYPE)
+    cost: Cost = Products().ashp_bundle_cost(ashp_cost_inputs(epc))
     return MeasureOption(
         measure_type=_ASHP_MEASURE_TYPE,
         description=(
@@ -222,9 +225,7 @@ def _ashp_option(
             "temperature-zone controls and a heat-pump hot-water cylinder"
         ),
         overlay=EpcSimulation(heating=_ASHP_OVERLAY),
-        cost=Cost(
+        cost=cost,
-            total=product.unit_cost_per_m2, contingency_rate=product.contingency_rate
-        ),
         material_id=product.id,
     )
 

tests/domain/modelling/test_heating_recommendation.py

@@ -12,6 +12,9 @@ from domain.modelling.product import Product
 from domain.modelling.recommendation import Recommendation
 from domain.modelling.simulation import HeatingOverlay
 from repositories.product.product_repository import ProductRepository
+from tests.domain.modelling._elmhurst_recommendation import (
+    parse_recommendation_summary,
+)
 from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
     build_epc,
 )
@@ -152,7 +155,7 @@ def test_gas_boiler_house_yields_an_ashp_bundle() -> None:
     assert options["air_source_heat_pump"].overlay.heating == HeatingOverlay(
         main_fuel_type=30,
         main_heating_control=2210,
-        main_heating_index_number=101413,
+        main_heating_index_number=110257,
         main_heating_category=4,
         water_heating_code=901,
         water_heating_fuel=30,
@@ -166,6 +169,28 @@ def test_gas_boiler_house_yields_an_ashp_bundle() -> None:
     )
 
 
+def test_ashp_bundle_carries_the_composite_per_dwelling_cost() -> None:
+    # Arrange — a mains-gas regular boiler with a cylinder (90 m2, 7 habitable
+    # rooms): the ASHP reuses the existing wet system (ADR-0025).
+    epc: EpcPropertyData = parse_recommendation_summary(
+        "ashp_from_system_boiler_with_cylinder_001431_before.pdf"
+    )
+
+    # Act
+    recommendation: Recommendation | None = recommend_heating(epc, _StubProducts())
+    assert recommendation is not None
+    option = next(
+        o for o in recommendation.options if o.measure_type == "air_source_heat_pump"
+    )
+
+    # Assert — composite: decommission (gas) 720 + pump (4.5 kW band) 9720 +
+    # cylinder 2382.60 + reuse distribution (flush 168 + 0.5 x dist(10) 5220 =
+    # 2778) = 15600.60, with the separate 25% ASHP contingency.
+    assert option.cost is not None
+    assert abs(option.cost.total - 15600.60) <= 1e-9
+    assert abs(option.cost.contingency_rate - 0.25) <= 1e-9
+
+
 def test_listed_building_yields_no_ashp_bundle() -> None:
     # Arrange — a listed building protects the fabric; an external ASHP unit is
     # not auto-offered (ADR-0024). The dwelling is on gas, so HHRSH is also out.