feat(modelling): Score carries the scored SapResult for billing

Score gains sap_result: Optional[SapResult], populated by PackageScorer with the
calculator output its headline figures came from. This lets the Modelling stage
price the post-package (and baseline) end-state via Bill Derivation reusing a
SapResult already computed by the optimiser's re-score / the orchestrator's
baseline score — no second calculate (ADR-0014 amendment). The optimiser reads
only sap_continuous, so it stays domain-agnostic and the stub scorers (which omit
sap_result) are unaffected — all optimiser tests pass unchanged.

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

domain/modelling/scoring/package_scorer.py

@@ -8,7 +8,7 @@ user-assembled plan.
 """
 
 from dataclasses import dataclass
-from typing import Sequence
+from typing import Optional, Sequence
 
 from datatypes.epc.domain.epc_property_data import EpcPropertyData
 from domain.modelling.scoring.overlay_applicator import apply_simulations
@@ -20,11 +20,18 @@ from domain.sap10_calculator.calculator import SapCalculator, SapResult
 class Score:
     """The headline metrics of a scored package. `sap_continuous` is the
     un-rounded SAP rating (used for deltas); carbon and primary energy are the
-    annual totals."""
+    annual totals.
+
+    `sap_result` is the calculator output the headline figures were taken from,
+    carried so Bill Derivation can price the scored end-state without a second
+    `calculate` (ADR-0014 amendment). The optimiser never reads it — it works
+    off `sap_continuous` only — so it stays domain-agnostic and a stub scorer
+    may leave it `None`."""
 
     sap_continuous: float
     co2_kg_per_yr: float
     primary_energy_kwh_per_yr: float
+    sap_result: Optional[SapResult] = None
 
 
 class PackageScorer:
@@ -44,4 +51,5 @@ class PackageScorer:
             sap_continuous=result.sap_score_continuous,
             co2_kg_per_yr=result.co2_kg_per_yr,
             primary_energy_kwh_per_yr=result.primary_energy_kwh_per_yr,
+            sap_result=result,
         )

tests/domain/modelling/test_package_scorer.py

@@ -52,3 +52,20 @@ def test_empty_package_scores_the_unmodified_baseline() -> None:
         abs(score.primary_energy_kwh_per_yr - direct.primary_energy_kwh_per_yr)
         <= 1e-9
     )
+
+
+def test_score_carries_the_scored_sap_result_for_billing() -> None:
+    # Arrange — the post-package SapResult must ride on the Score so Bill
+    # Derivation can price the simulated end-state without a second calculate
+    # (ADR-0014 amendment).
+    baseline: EpcPropertyData = build_epc()
+    scorer = PackageScorer(Sap10Calculator())
+
+    # Act
+    filled: Score = scorer.score(baseline, [_CAVITY_FILL])
+
+    # Assert — the SapResult is the one the Score's headline figures came from.
+    assert filled.sap_result is not None
+    assert (
+        abs(filled.sap_result.sap_score_continuous - filled.sap_continuous) <= 1e-9
+    )