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

Slice 3 of the lighting generator (ADR-0023): two real Elmhurst before/after
cascade pins, sourced from the low_energy_lighting recommendation folder. Both
close cleanly at 1e-4 with NO xfail — lighting changes only bulb counts →
Appendix L (232), no fabric coupling (contrast glazing's draught-proofing).
  - zero existing LEDs: 20 incandescent → 20 LED
  - some existing LEDs: 5 LED + 15 incandescent → 20 LED (partial-upgrade path)
The overlay-emits-correct-counts assertion lives in the Slice 2 unit tests.

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

tests/domain/modelling/test_elmhurst_cascade_pins.py

@@ -37,6 +37,7 @@ from domain.modelling.generators.solid_wall_recommendation import (
     recommend_solid_wall,
 )
 from domain.modelling.generators.glazing_recommendation import recommend_glazing
+from domain.modelling.generators.lighting_recommendation import recommend_lighting
 from domain.modelling.scoring.overlay_applicator import apply_simulations
 from domain.modelling.recommendation import MeasureOption
 from domain.sap10_calculator.calculator import Sap10Calculator, SapResult
@@ -537,3 +538,41 @@ def test_secondary_glazing_overlay_reproduces_the_relodged_after() -> None:
     _assert_overlay_reproduces_after(
         before, after, recommendation.options[0].overlay
     )
+
+
+def test_lighting_overlay_reproduces_the_relodged_after_zero_existing_leds() -> None:
+    # Arrange — a dwelling with no LEDs (20 incandescent); the after re-lodges
+    # all 20 as LED. Lighting only changes bulb counts → Appendix L (232), with
+    # no fabric coupling, so the full-SAP pin closes cleanly.
+    before: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_zero_leds_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_zero_leds_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_lighting(before, _AnyProduct())
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )
+
+
+def test_lighting_overlay_reproduces_the_relodged_after_some_existing_leds() -> None:
+    # Arrange — a dwelling with some LEDs already (5 LED + 15 incandescent); the
+    # after re-lodges all 20 as LED. Exercises the partial-upgrade path: the
+    # overlay tops led up to the total rather than starting from zero.
+    before: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_some_leds_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_some_leds_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_lighting(before, _AnyProduct())
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )