Treat solar block without array sizing as no-solar (fix KeyError)

2 modelling_e2e properties failed with KeyError: 'maxArrayPanelsCount'.

Google returns a `solarPotential` block with no array-level sizing fields
(`maxArrayPanelsCount` / `panelCapacityWatts`) for buildings with no usable
solar estimate. `SolarPotential.from_building_insights` hard-indexed those keys
and crashed the whole property.

Fix: the projection now returns Optional and yields None when those fields are
absent — the established "no solar potential" outcome (the orchestrator and
recommendation path already type it Optional and skip solar on None). Existing
callers (`_solar_potential_for`, harness) already assign to Optional.

Regression test + `assert is not None` narrowing on the valid-fixture tests.

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

domain/modelling/solar_potential.py

@@ -19,7 +19,7 @@ Potential).
 from __future__ import annotations
 
 from dataclasses import dataclass
-from typing import Any, Mapping
+from typing import Any, Mapping, Optional
 
 # Google's `azimuthDegrees` is a compass bearing: 0°=N, 90°=E, 180°=S, 270°=W,
 # increasing clockwise. The SAP octant codes (ORIENTATION_BY_SAP10_CODE in the
@@ -96,10 +96,21 @@ class SolarPotential:
     configurations: tuple[SolarPanelConfiguration, ...]
 
     @classmethod
-    def from_building_insights(cls, insights: Mapping[str, Any]) -> "SolarPotential":
+    def from_building_insights(
+        cls, insights: Mapping[str, Any]
+    ) -> Optional["SolarPotential"]:
         """Project a raw Google ``buildingInsights`` response (as persisted by
-        `SolarRepository`) into a `SolarPotential`."""
+        `SolarRepository`) into a `SolarPotential`, or None when the
+        ``solarPotential`` block lacks the array-level sizing fields
+        (``maxArrayPanelsCount`` / ``panelCapacityWatts``) — Google returns such
+        partial blocks for buildings with no usable solar estimate, which is a
+        "no solar potential" outcome, not a hard error."""
         solar_potential: Mapping[str, Any] = insights["solarPotential"]
+        if (
+            "maxArrayPanelsCount" not in solar_potential
+            or "panelCapacityWatts" not in solar_potential
+        ):
+            return None
         configurations: tuple[SolarPanelConfiguration, ...] = tuple(
             SolarPanelConfiguration(
                 panels_count=int(config["panelsCount"]),

tests/domain/modelling/test_solar_config_selection.py

@@ -46,6 +46,7 @@ def _segment(panels: int, azimuth: float, energy: float) -> SolarRoofSegment:
 def test_real_example_samples_five_spanning_configs() -> None:
     # Arrange
     potential = SolarPotential.from_building_insights(_insights())
+    assert potential is not None
 
     # Act
     configs = select_conservative_configs(potential)

tests/domain/modelling/test_solar_overshading.py

@@ -77,6 +77,7 @@ def test_segment_overshading_recovers_each_bucket() -> None:
 def test_real_example_segments_are_unshaded() -> None:
     # Arrange
     potential = SolarPotential.from_building_insights(_insights())
+    assert potential is not None
     largest = potential.configurations[-1]
 
     # Act

tests/domain/modelling/test_solar_potential.py

@@ -54,6 +54,20 @@ def test_pitch_to_sap_code_snaps_to_rdsap_enum() -> None:
     assert pitch_to_sap_code(31.896425) == 2
 
 
+def test_projection_returns_none_when_array_sizing_absent() -> None:
+    # Arrange — Google returns a solarPotential block with no array-sizing
+    # fields for buildings with no usable solar estimate; this previously
+    # KeyError'd on `maxArrayPanelsCount` and failed the whole property.
+    insights = _insights()
+    del insights["solarPotential"]["maxArrayPanelsCount"]
+
+    # Act
+    potential = SolarPotential.from_building_insights(insights)
+
+    # Assert — no usable solar potential, not a crash
+    assert potential is None
+
+
 def test_projection_reads_potential_level_fields() -> None:
     # Arrange
     insights = _insights()
@@ -62,6 +76,7 @@ def test_projection_reads_potential_level_fields() -> None:
     potential = SolarPotential.from_building_insights(insights)
 
     # Assert
+    assert potential is not None
     assert abs(potential.panel_capacity_watts - 400.0) <= 1e-4
     assert potential.max_array_panels_count == 49
     assert len(potential.configurations) == 46
@@ -73,6 +88,7 @@ def test_projection_first_config_single_segment() -> None:
 
     # Act
     potential = SolarPotential.from_building_insights(insights)
+    assert potential is not None
     first = potential.configurations[0]
 
     # Assert — the smallest rung: 4 panels on one SE roof plane
@@ -93,6 +109,7 @@ def test_projection_largest_config_spans_all_segments() -> None:
 
     # Act
     potential = SolarPotential.from_building_insights(insights)
+    assert potential is not None
     largest = potential.configurations[-1]
 
     # Assert — the 49-panel rung spans all four roof planes

tests/domain/modelling/test_solar_recommendation.py

@@ -44,7 +44,9 @@ class _StubProducts(ProductRepository):
 def _solar_potential() -> SolarPotential:
     with _FIXTURE.open(encoding="utf-8") as handle:
         data: dict[str, Any] = json.load(handle)
-    return SolarPotential.from_building_insights(data)
+    potential = SolarPotential.from_building_insights(data)
+    assert potential is not None
+    return potential
 
 
 def _eligible_house() -> EpcPropertyData: