Audit: pin u_roof description cascade against RdSAP10 Table 16 for golden cert cohort

Mirror of the wall cohort pin. Worksheet fixtures lodge roofs=[] so the description-driven branch of u_roof was never validated at cascade level. New parametrised test pins 8 (description, age, thickness) tuples from the golden certs against the Table 16 col-1 (loft insulation thickness known) value. All 8 cases match spec: u_roof is correct on the thickness-known path even when joined-description from multiple roof rows contains noise.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/domain/src/domain/ml/tests/test_rdsap_uvalues.py

@@ -1230,3 +1230,56 @@ def test_u_wall_matches_table6_for_every_cohort_description_age_pair(
 
     # Assert
     assert abs(u - expected_u) < 1e-4
+
+
+# ----- Description-cascade cohort pins (Roofs) -----
+#
+# Mirror of the wall cohort pins above. The Elmhurst worksheet fixtures
+# lodge `roofs=[]`, so the cascade-pin tests do not exercise u_roof's
+# description path either. The 8 golden API certs lodge `roofs[].
+# description` strings — these tests pin each (description, age,
+# thickness) tuple seen in that cohort against the RdSAP10 Table 16
+# (loft-insulation-thickness-known) value the spec mandates.
+#
+# Excluded: ambiguous joined-description cases where one bp lodges no
+# thickness and another lodges a value — the calc routes through Table
+# 18 defaults whose interaction with the description cascade needs
+# separate pinning. "(another dwelling above)" is also excluded — its
+# u_roof value is ignored by heat_transmission once roof_area is zeroed.
+_TABLE_16_ENG_ROOF_COHORT_PINS: tuple[tuple[str, str, int, float], ...] = (
+    # (joined_description, age_band, thickness_mm, expected_u_w_per_m2k)
+    # Table 16 col 1 — thickness-known path, U independent of age band.
+    ("Pitched, 100 mm loft insulation",                                          "D", 100, 0.40),  # cert 7536 bp0
+    ("Pitched, 100 mm loft insulation | Pitched, insulated (assumed)",           "D", 100, 0.40),  # cert 7536 bp0 (joined)
+    ("Pitched, 270 mm loft insulation",                                          "D", 270, 0.16),  # cert 0300 bp0
+    ("Pitched, 300 mm loft insulation | Flat, no insulation",                    "D", 300, 0.14),  # cert 0390-2954 bp0
+    ("Pitched, 300 mm loft insulation | Roof room(s), limited insulation (assumed)", "A", 300, 0.14),  # cert 6035 bp0
+    ("Pitched, 300 mm loft insulation | Flat, insulated",                        "C", 300, 0.14),  # cert 8135 bp0
+    ("Pitched, 300 mm loft insulation | Pitched, 100 mm loft insulation",        "B", 300, 0.14),  # cert 2130 bp0
+    ("Pitched, 400+ mm loft insulation | Pitched, insulated (assumed)",          "J", 400, 0.11),  # cert 0240 bp0
+)
+
+
+@pytest.mark.parametrize(
+    "description, age_band, thickness_mm, expected_u",
+    _TABLE_16_ENG_ROOF_COHORT_PINS,
+)
+def test_u_roof_matches_table16_for_every_cohort_description_thickness_pair(
+    description: str,
+    age_band: str,
+    thickness_mm: int,
+    expected_u: float,
+) -> None:
+    # Arrange — inputs replicate what `heat_transmission_from_cert` feeds
+    # `u_roof` for the main building part in the golden cert cohort.
+
+    # Act
+    u = u_roof(
+        country=Country.ENG,
+        age_band=age_band,
+        insulation_thickness_mm=thickness_mm,
+        description=description,
+    )
+
+    # Assert
+    assert abs(u - expected_u) < 1e-4