Source the off-peak meter flag and main-heating fraction from the cert 🟩

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

domain/sap10_calculator/rdsap/cert_to_inputs.py

@@ -8154,6 +8154,17 @@ def cert_to_inputs(
         eff,
     )
 
+    # ADR-0014 Bill Derivation — Off-Peak Meter day/night billing metadata.
+    # The off-peak `_fuel_cost` path returns the zero `FuelCostResult` (deferring
+    # to the legacy scalar rates), so the bill's per-end-use High-Rate Fractions
+    # are sourced here from the SAME Table 12a helpers the scalar cost path uses,
+    # keeping the bill's day/night split identical to the rating's.
+    _billing_tariff = _rdsap_tariff(epc)
+    _is_off_peak_meter = _billing_tariff is not Tariff.STANDARD
+    _main_high_rate_fraction = _main_space_heating_high_rate_fraction(
+        main, _billing_tariff
+    )
+
     return CalculatorInputs(
         dimensions=dim,
         heat_transmission=ht,
@@ -8218,6 +8229,8 @@ def cert_to_inputs(
         ),
         secondary_heating_fuel_code=_secondary_fuel_code(epc),
         hot_water_fuel_code=_water_heating_fuel_code(epc),
+        is_off_peak_meter=_is_off_peak_meter,
+        main_heating_high_rate_fraction=_main_high_rate_fraction,
         space_heating_fuel_cost_gbp_per_kwh=_space_heating_fuel_cost_gbp_per_kwh(
             main, _rdsap_tariff(epc), prices
         ),

tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py

@@ -836,6 +836,42 @@ def test_integrated_storage_heater_408_bills_table_12a_grid1_high_rate_fraction(
     assert abs(inputs.space_heating_fuel_cost_gbp_per_kwh - 0.07458) <= 1e-9
 
 
+def test_off_peak_storage_cert_surfaces_billing_meter_flag_and_main_fraction() -> None:
+    # Arrange — the same integrated-storage (code 408) Economy-7 cert. For
+    # ADR-0014 Bill Derivation, cert_to_inputs surfaces the Off-Peak Meter flag
+    # and the main-heating High-Rate Fraction — the SAME Table 12a Grid 1 value
+    # (0.20) the SAP cost path blends above, so the bill never re-derives it.
+    from dataclasses import replace
+
+    main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=29,  # electricity
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2401,
+        main_heating_category=7,  # electric storage heaters
+        sap_main_heating_code=408,
+    )
+    base = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2,
+        habitable_rooms_count=4,
+        country_code="ENG",
+        sap_building_parts=[make_building_part(construction_age_band="E")],
+        sap_heating=make_sap_heating(main_heating_details=[main]),
+    )
+    epc = replace(
+        base,
+        sap_energy_source=replace(base.sap_energy_source, meter_type="1"),  # Dual
+    )
+
+    # Act
+    inputs = cert_to_inputs(epc)
+
+    # Assert — whole-meter off-peak, main heating high-rate fraction 0.20.
+    assert inputs.is_off_peak_meter is True
+    assert inputs.main_heating_high_rate_fraction == 0.20
+
+
 def test_off_peak_immersion_unlodged_type_defaults_to_dual_table13_blend() -> None:
     # Arrange — electric immersion DHW (WHC 903) on a Dual / Economy-7 (7-hour)
     # meter with a cylinder present (Normal / 110 L), but the cert does NOT lodge