fix(uvalues): cap as-built stone U at age E only, not A-E; drop insulation-state gate (RdSAP 10 Tables 6-7 footnote a, PDF p.33-35)

Commit 034d4b7c corrected two stone cases but via the wrong mechanism: it
removed the 1.7 cap for ALL age bands and gated the §5.6 formula on
`wall_insulation_type is not None`. Both diverge from RdSAP 10 Tables 6-10:

- The stone rows read "According to 5.6" for bands A-D (uncapped formula)
  and "1.7 a" at band E, where footnote (a) = "Or from equations in 5.6 if
  the calculated U-value is less than 1.7" → U_E = min(formula, 1.7). The
  cap belongs ONLY at age E. Removing it for E let an as-built 50 mm granite
  age-E wall return the formula's 6.09 instead of 1.70.
- Scotland sandstone/limestone age E defaults to 1.5 (Table 7, PDF p.35);
  granite/whinstone stays 1.7.
- The insulation-state gate is not a spec rule. It sent age-A-D stone with
  "insulation Unknown" (wall_insulation_type None) to the flat-1.7 table
  instead of the §5.6 formula; it only "worked" for fixture 000565 Ext1
  because that wall is age E, where 1.7 is correct anyway. Removed: the
  age-E cap, not the gate, is what produces 000565 Ext1's worksheet 1.70.

Bands A-D stay uncapped (sandstone 400 mm → 1.90, granite 120 mm → 3.89).
Unknown-thickness handling unchanged in this commit (still flat-table; the
§3.5 Table-3 default follows separately).

pyright not installed in this container — strict type gate not run locally.

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

domain/sap10_ml/rdsap_uvalues.py

@@ -567,30 +567,43 @@ def u_wall(
     ctry = country if country is not None else Country.ENG
     age_idx = _age_index(age_band)
     band = _AGE_BANDS[age_idx]
-    # RdSAP 10 §5.6 (PDF p.40) — uninsulated stone wall formula, age
+    # RdSAP 10 Tables 6-10 stone rows + footnote (a) (PDF p.33-39), §5.6
-    # bands A-E. Fires only when (a) a documentary wall thickness is lodged
+    # formula (PDF p.40), §5.8 + Table 14 (PDF p.41-42). A documentary wall
-    # (per §5.3 documentary-evidence rule) AND (b) the insulation STATE is
+    # thickness (per §5.3) routes stone in age bands A-E off the §5.6 formula,
-    # known (`wall_insulation_type` not None — As Built / external / internal).
+    # NOT the flat Table-6 typical-thickness default:
-    # When either is absent the cascade falls through to the Table-6
+    #   - Bands A-D: pure §5.6 formula, UNCAPPED. The stone rows read
-    # typical-thickness default (1.7) below: an "insulation Unknown" lodgement
+    #     "According to 5.6" with NO 1.7 entry, because a thin/standard solid
-    # is NOT treated as bare stone of the lodged thickness (cert 000565 Ext1:
+    #     stone wall genuinely loses more than the typical default (sandstone
-    # granite 50 mm + insulation Unknown → Table-6 1.70 in the worksheet, NOT
+    #     400 mm → 1.90, granite 120 mm → 3.89).
-    # the §5.6 formula's 6.09), and the footnote (a) "use §5.6 if the
+    #   - Band E: the stone row reads "1.7 a"; footnote (a) = "Or from
-    # calculated U-value is less than 1.7" clause governs the unknown path. When the thickness IS
+    #     equations in 5.6 if the calculated U-value is less than 1.7" →
-    # lodged the raw §5.6 U is the spec target — it is NOT capped at 1.7,
+    #     U_E = min(formula, 1.7). Scotland sandstone/limestone age E defaults
-    # because a thin/standard solid stone wall genuinely loses more than the
+    #     to 1.5 (Table 7), granite/whinstone stays 1.7. The 1.7 (1.5) cap
-    # typical-thickness default (sandstone 400 mm → 1.90, granite 120 mm →
+    #     belongs ONLY at age E, never A-D.
-    # 3.89). §5.8 + Table 14 insulation / dry-line adjustments apply on top
+    # The insulation STATE is NOT a gate: an "as built / insulation Unknown"
-    # of the raw §5.6 U₀ (cert 000565 Main alt_wall_1: granite W=120 mm
+    # lodgement (`wall_insulation_type` None or 4) takes the formula too. Cert
-    # dry-lined → U₀=3.88 + dry-line → 2.34, matches worksheet).
+    # 000565 Ext1 (granite 50 mm, age E, insulation Unknown) → min(6.09, 1.7)
+    # = 1.70, matching the U985 worksheet WITHOUT a flat-table detour — the
+    # age-E cap, not an insulation gate, is what produces the 1.70.
     if (
         wall_thickness_mm is not None
-        and wall_insulation_type is not None
         and band in _STONE_AGE_A_TO_E
         and construction in (WALL_STONE_GRANITE, WALL_STONE_SANDSTONE)
     ):
         u0 = _u_stone_thin_wall_age_a_to_e(construction, wall_thickness_mm)
         if u0 is not None:
+            # Footnote (a) cap is age-E only: clamp the as-built U to the
+            # Table-6/7 age-E default (1.7, or 1.5 for Scotland sandstone/
+            # limestone) when the §5.6 formula exceeds it. A-D stay uncapped.
+            if band == "E":
+                e_default = (
+                    1.5
+                    if ctry == Country.SCT
+                    and construction == WALL_STONE_SANDSTONE
+                    else 1.7
+                )
+                if u0 >= e_default:
+                    u0 = e_default
             # RdSAP 10 §5.8 + Table 14 (PDF p.41-42) — added External/Internal
             # insulation on a stone wall: U = 1/(1/U₀ + R_ins), with U₀ the
             # RAW §5.6 stone result (the Table-6 footnote (a) 1.7 cap does NOT
@@ -630,15 +643,12 @@ def u_wall(
                         Decimal("0.01"), rounding=ROUND_HALF_UP
                     )
                 )
-            # As-built (uninsulated, not dry-lined) stone wall of KNOWN
+            # As-built (uninsulated, not dry-lined) stone wall, age A-E:
-            # thickness, age A-E: return the raw §5.6 result. The Table-6
+            # return the §5.6 result — uncapped for A-D, age-E-capped above.
-            # footnote (a) "< 1.7" clause governs the UNKNOWN-thickness path
+            # A thin solid stone wall genuinely has U > 1.7 (sandstone 400 mm
-            # (which falls through to the Table-6 typical 1.7 default below) —
+            # = 1.90, granite 120 mm = 3.89); capping A-D to 1.7 under-counts
-            # NOT a documentary-thickness lodgement. A thin solid stone wall
+            # fabric loss and over-rates. Confirmed against Elmhurst (age-B
-            # genuinely has U > 1.7 (e.g. sandstone 400 mm = 1.90, granite
+            # sandstone 400 mm → 1.90) and the §5.6 Table-12 formula tests.
-            # 120 mm = 3.89); capping it to 1.7 under-counts fabric loss and
-            # over-rates. Confirmed against Elmhurst (age-B sandstone 400 mm
-            # → 1.9) and the §5.6 Table-12 formula tests.
             return u0
     known_types = {
         WALL_STONE_GRANITE, WALL_STONE_SANDSTONE, WALL_SOLID_BRICK, WALL_CAVITY,

domain/sap10_ml/tests/test_rdsap_uvalues.py

@@ -849,6 +849,96 @@ def test_u_wall_stone_granite_age_a_without_wall_thickness_returns_table_6_age_a
     assert abs(result - 1.7) <= 1e-3
 
 
+def test_u_wall_stone_granite_age_e_50mm_caps_at_table6_default_1_7() -> None:
+    # Arrange — RdSAP 10 Table 6 (England, PDF p.33-34) stone row reads
+    # "1.7 a" at age E, footnote (a) = "Or from equations in 5.6 if the
+    # calculated U-value is less than 1.7". A 50 mm granite wall's §5.6
+    # formula gives U = 45.315 × 50^(-0.513) = 6.09 (> 1.7), so the age-E
+    # default 1.7 stands → min(6.09, 1.7) = 1.70. The cap is age-E ONLY:
+    # bands A-D are uncapped (120 mm age-A granite = 3.89). Insulation is
+    # Unknown (wall_insulation_type None) — no longer a gate. Cert 000565
+    # BP Ext1 is this fixture (U985 worksheet U = 1.70).
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="E",
+        construction=WALL_STONE_GRANITE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=50,
+    )
+
+    # Assert
+    assert abs(result - 1.70) <= 1e-3
+
+
+def test_u_wall_stone_sandstone_age_e_thick_wall_uses_5_6_formula_below_1_7() -> None:
+    # Arrange — footnote (a) at age E: use the §5.6 formula when it gives
+    # < 1.7. A 600 mm sandstone wall → U = 54.876 × 600^(-0.561) = 1.5165
+    # (< 1.7), so the formula value is used, NOT the 1.7 default.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="E",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=600,
+    )
+
+    # Assert
+    assert abs(result - 1.5165) <= 1e-3
+
+
+def test_u_wall_stone_sandstone_scotland_age_e_caps_at_1_5_not_1_7() -> None:
+    # Arrange — RdSAP 10 Table 7 (Scotland, PDF p.35) sandstone/limestone
+    # age E default is "1.5 a" (granite/whinstone stays 1.7). A 500 mm
+    # sandstone wall's §5.6 formula = 54.876 × 500^(-0.561) = 1.68 (> 1.5),
+    # so the Scotland age-E default 1.5 stands → min(1.68, 1.5) = 1.50.
+
+    # Act
+    result = u_wall(
+        country=Country.SCT,
+        age_band="E",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=500,
+    )
+
+    # Assert
+    assert abs(result - 1.50) <= 1e-3
+
+
+def test_u_wall_stone_granite_scotland_age_e_50mm_stays_capped_at_1_7() -> None:
+    # Arrange — Scotland granite/whinstone age E default is 1.7 (only
+    # sandstone/limestone drops to 1.5, Table 7 PDF p.35). A 50 mm granite
+    # wall's formula 6.09 (> 1.7) → min(6.09, 1.7) = 1.70, NOT 1.5.
+
+    # Act
+    result = u_wall(
+        country=Country.SCT,
+        age_band="E",
+        construction=WALL_STONE_GRANITE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=50,
+    )
+
+    # Assert
+    assert abs(result - 1.70) <= 1e-3
+
+
 def test_u_wall_curtain_wall_missing_age_lodgement_defaults_to_pre_2023_u_2p0_per_rdsap_5_18() -> None:
     # Arrange — when the cert lodges `Type: CW Curtain Wall` but no
     # `Curtain Wall Age` line (older Elmhurst Summary PDFs, or API EPCs