test(modelling): HHRSH before/after cascade pins (001431) at 1e-4

The same absolute-target HHR overlay reproduces the common relodged after from
two different base systems (existing electric storage; "no system present"
electric) — proving the bundle is a true whole-system end-state. Closes one
named gap the pin surfaced: the relodged HHR cylinder lodges
cylinder_thermostat='Y', so HeatingOverlay + _fold_heating + the HHRSH overlay
gain cylinder_thermostat (ΔSAP 0.065 -> <1e-4). ADR-0024.

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

domain/modelling/generators/heating_recommendation.py

@@ -46,6 +46,7 @@ _HHR_STORAGE_OVERLAY = HeatingOverlay(
     cylinder_size=2,
     cylinder_insulation_type=1,
     cylinder_insulation_thickness_mm=120,
+    cylinder_thermostat="Y",
     has_hot_water_cylinder=True,
     meter_type="Dual",
 )
@@ -98,6 +99,6 @@ def _hhr_storage_eligible(epc: EpcPropertyData) -> bool:
         return False
     if main.main_heating_category == _HEAT_PUMP_CATEGORY:
         return False
-    off_gas: bool = epc.sap_energy_source is None or not epc.sap_energy_source.mains_gas
+    off_gas: bool = not epc.sap_energy_source.mains_gas
     electric_main: bool = main.main_fuel_type == _ELECTRICITY_FUEL
     return electric_main or off_gas

domain/modelling/scoring/overlay_applicator.py

@@ -74,6 +74,7 @@ _SAP_HEATING_FIELDS: tuple[str, ...] = (
     "cylinder_size",
     "cylinder_insulation_type",
     "cylinder_insulation_thickness_mm",
+    "cylinder_thermostat",
 )
 _ENERGY_SOURCE_FIELDS: tuple[str, ...] = ("meter_type", "mains_gas")
 

domain/modelling/simulation.py

@@ -120,6 +120,7 @@ class HeatingOverlay:
     cylinder_size: Optional[Union[int, str]] = None
     cylinder_insulation_type: Optional[Union[int, str]] = None
     cylinder_insulation_thickness_mm: Optional[int] = None
+    cylinder_thermostat: Optional[str] = None
     # EpcPropertyData (top-level)
     has_hot_water_cylinder: Optional[bool] = None
     # sap_energy_source

tests/domain/modelling/test_elmhurst_cascade_pins.py

@@ -38,6 +38,7 @@ from domain.modelling.generators.solid_wall_recommendation import (
 )
 from domain.modelling.generators.glazing_recommendation import recommend_glazing
 from domain.modelling.generators.lighting_recommendation import recommend_lighting
+from domain.modelling.generators.heating_recommendation import recommend_heating
 from domain.modelling.scoring.overlay_applicator import apply_simulations
 from domain.modelling.recommendation import MeasureOption
 from domain.sap10_calculator.calculator import Sap10Calculator, SapResult
@@ -576,3 +577,46 @@ def test_lighting_overlay_reproduces_the_relodged_after_some_existing_leds() ->
     _assert_overlay_reproduces_after(
         before, after, recommendation.options[0].overlay
     )
+
+
+def test_hhr_storage_overlay_reproduces_the_relodged_after_from_electric_storage() -> None:
+    # Arrange — an existing electric storage system re-lodged as high-heat-
+    # retention storage (Table 4a 402 -> 409, control 2401 -> 2404), gaining an
+    # off-peak immersion cylinder and a dual meter (ADR-0024).
+    before: EpcPropertyData = parse_recommendation_summary(
+        "hhr_storage_from_electric_storage_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "hhr_storage_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_heating(before, _AnyProduct())
+    assert recommendation is not None
+    option = next(
+        o
+        for o in recommendation.options
+        if o.measure_type == "high_heat_retention_storage_heaters"
+    )
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(before, after, option.overlay)
+
+
+def test_hhr_storage_overlay_reproduces_the_relodged_after_from_no_system() -> None:
+    # Arrange — a "no system present" electric dwelling re-lodged as HHR storage;
+    # the same absolute-target overlay must reproduce the common after.
+    before: EpcPropertyData = parse_recommendation_summary(
+        "hhr_storage_from_no_system_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "hhr_storage_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_heating(before, _AnyProduct())
+    assert recommendation is not None
+    option = next(
+        o
+        for o in recommendation.options
+        if o.measure_type == "high_heat_retention_storage_heaters"
+    )
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(before, after, option.overlay)

tests/domain/modelling/test_heating_recommendation.py

@@ -62,6 +62,7 @@ def test_electric_storage_dwelling_yields_an_hhr_storage_bundle() -> None:
         cylinder_size=2,
         cylinder_insulation_type=1,
         cylinder_insulation_thickness_mm=120,
+        cylinder_thermostat="Y",
         has_hot_water_cylinder=True,
         meter_type="Dual",
     )