Slice 26c: §7 mean internal temperature cascade pin (44/60 PASS)

Added `mean_internal_temperature_section_from_cert` composing §1 (dim)
+ §2 (effective_monthly_ach) + §3 (total HLC) + §5 (internal gains)
+ §6 (solar gains) + climate (external temp) and threading them through
the §7 orchestrator — exact mirror of the cert_to_inputs internal
cascade.

Added 60 strict pin cases for §7 worksheet lines (85)..(94): T_h1
scalar, living_area_fraction scalar, η_living + T_living + T_h2 +
η_elsewhere + T_elsewhere + T_92 + T_93 + η_whole monthly tuples.

§7 per-fixture monthly pin status:
  fixture | passing
  000474  | 6 of 8  (LINE_92/93 ~0.0001 K residual)
  000477  | 6 of 8  (LINE_92/93 ~0.0002 K residual)
  000480  | 6 of 8  (LINE_92/93 ~0.0001 K residual)
  000487  | 0 of 8  (cascade from §3 RR + §4 HW defects)
  000490  | 6 of 8  (LINE_92/93 ~0.0001 K residual)
  000516  | 8 of 8  ✓

LINE_92/93 marginal fails on 4 fixtures: weighted-sum of T_living +
T_elsewhere drifts by ~1e-4 K from PDF despite the per-zone temps
matching at 1e-4 individually. Likely a PDF intermediate-precision
artefact (analogous to U_eff at 5 dp in §3 windows); investigation
deferred — no widening per project policy.

Scoreboard:
  section_cascade_pins: 230 → 274 PASS (+44; 60 new tests, 16 fail)
  e2e SapResult:         32 →  32 PASS (unchanged — §7 cascade was
    already running internally, pin tests just surface the line refs)

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

docs/sap-spec/HANDOVER_NEXT.md

@@ -133,12 +133,14 @@ Two test files contain the strict pins:
 Total: **169 PASS / 83 FAIL** across the strict pins. 4 of 6 fixtures fully
 close §1+§2+§4. 000487 is the worst (RR fixture defect propagates everywhere).
 
-(Post-slice-26b: section_cascade_pins 230 PASS / 22 FAIL, e2e SapResult
-32 PASS / 40 FAIL. §3 + §5 + §6 fully close for 5 of 6 fixtures at
-abs=1e-4. Remaining cascade failures: §4 monthly (000477/487 HW defects,
-slice 25), §5 LINE_72/73 + §6 LINE_84 on 000477/487 (cascaded from §4),
-§3 (000487 RR defect, slice 25), and downstream SapResult pins still
-drifting because of §7–§9a precision not yet pinned.)
+(Post-slice-26c: section_cascade_pins 274 PASS / 38 FAIL, e2e SapResult
+32 PASS / 40 FAIL. §3 + §5 + §6 + §7 (mostly) pinned. §7 LINE_85..91
++ LINE_87/88/89/90 close at abs=1e-4 for all 5 non-487 fixtures.
+LINE_92/93 marginal residuals (~0.0001 K, just over threshold) on
+000474/477/480/490 — investigation needed (possible PDF intermediate
+rounding precision artefact). 000487 fully cascades from §3/§4 defects
+(slice 25). e2e SapResult unchanged because cert_to_inputs was already
+running the §7 calc internally — pin tests just surface it now.)
 
 ### B.2 SapResult pin matrix (post-slice-22/23)
 
@@ -199,6 +201,7 @@ fixture | section §4 pin status
 ### B.5 Recent slices (in reverse order — newest first)
 
 ```
+Slice 26c: §7 mean internal temp cascade pin (60 cases, 44 PASS) — LINE_85..94
 Slice 26b: §6 solar gains cascade pin (12 cases, 10 PASS) + SapRoofWindow solar attrs + plumb to §6 cascade
 Slice 26:  §5 internal gains cascade pin (54 cases, 50 PASS / 4 FAIL) + rooflight plumb to daylight factor
 Slice 27b: §3 element-area + door-area rounding to 2 d.p. per RdSAP10 §15 (p.66)
@@ -268,7 +271,7 @@ The cascade pin work continues in worksheet order. For each section:
 Sections still to pin:
 - ~~**§5 internal gains** (lines 66-73 + 232 lighting kWh)~~ DONE (slice 26)
 - ~~**§6 solar gains** (lines 83-84)~~ DONE (slice 26b — 5/6 fixtures close, 000477/487 cascade from §4)
-- **§7 mean internal temperature** (lines 85-94). 10 line refs, mostly monthly.
+- ~~**§7 mean internal temperature** (lines 85-94)~~ MOSTLY DONE (slice 26c — 44/60 PASS; LINE_92/93 marginal ~0.0001 K residual on 000474/477/480/490 needs investigation; 000487 cascades from §3/§4 defects).
 - **§8 space heating** (lines 95-99). 4 monthly + 2 annual.
 - **§9a energy requirements** (lines 201, 206-208, 211-215, 219). 5 scalar + 2
   monthly. Currently only the annual aggregates show on `SapResult` — may need

packages/domain/src/domain/sap/rdsap/cert_to_inputs.py

@@ -88,6 +88,7 @@ from domain.sap.worksheet.heat_transmission import (
 )
 from domain.sap.climate.appendix_u import external_temperature_c
 from domain.sap.worksheet.mean_internal_temperature import (
+    MeanInternalTemperatureResult,
     mean_internal_temperature_monthly,
 )
 from domain.sap.worksheet.energy_requirements import (
@@ -827,6 +828,54 @@ def _roof_windows_for_solar_gains(
     )
 
 
+def mean_internal_temperature_section_from_cert(
+    epc: EpcPropertyData,
+) -> Optional[MeanInternalTemperatureResult]:
+    """SAP 10.2 §7 cert→inputs cascade for `mean_internal_temperature_monthly`.
+
+    Composes §1 (dim) + §2 (effective_monthly_ach) + §3 (total HLC) + §5
+    (internal gains) + §6 (solar gains) + climate (external temp) and
+    threads them through the §7 orchestrator — exactly as cert_to_inputs
+    computes internally. Returns the full
+    `MeanInternalTemperatureResult` (every (85)..(94) line ref) so
+    cascade pin tests can assert each §7 line ref against the U985 PDF.
+
+    Returns `None` when TFA is missing (matches other section helpers).
+    """
+    if epc.total_floor_area_m2 is None:
+        return None
+    dim = dimensions_from_cert(epc)
+    ventilation = ventilation_from_cert(epc)
+    ht = heat_transmission_section_from_cert(epc)
+    ig = internal_gains_section_from_cert(epc)
+    sg = solar_gains_section_from_cert(epc)
+    assert ig is not None, "internal_gains None despite TFA present"
+    internal_gains_monthly_w = ig.total_internal_gains_monthly_w
+    solar_gains_monthly_w = sg.total_solar_gains_monthly_w
+    monthly_total_gains_w = tuple(
+        internal_gains_monthly_w[m] + solar_gains_monthly_w[m] for m in range(12)
+    )
+    monthly_htc_w_per_k = tuple(
+        ht.total_w_per_k + 0.33 * dim.volume_m3 * ventilation.effective_monthly_ach[m]
+        for m in range(12)
+    )
+    main = _first_main_heating(epc)
+    region = _region_index(epc.region_code)
+    return mean_internal_temperature_monthly(
+        monthly_external_temp_c=tuple(
+            external_temperature_c(region, m) for m in range(1, 13)
+        ),
+        monthly_total_gains_w=monthly_total_gains_w,
+        monthly_heat_transfer_coefficient_w_per_k=monthly_htc_w_per_k,
+        thermal_mass_parameter_kj_per_m2_k=_DEFAULT_THERMAL_MASS_PARAMETER_KJ_PER_M2_K,
+        total_floor_area_m2=dim.total_floor_area_m2,
+        control_type=_control_type(main),
+        responsiveness=_responsiveness(main),
+        living_area_fraction=_living_area_fraction(epc.habitable_rooms_count),
+        control_temperature_adjustment_c=0.0,
+    )
+
+
 def solar_gains_section_from_cert(epc: EpcPropertyData) -> SolarGainsResult:
     """SAP 10.2 §6 cert→inputs cascade for `solar_gains_from_cert`.
 

packages/domain/src/domain/sap/worksheet/tests/test_section_cascade_pins.py

@@ -20,6 +20,7 @@ from domain.sap.rdsap.cert_to_inputs import (
     cert_to_inputs,
     heat_transmission_section_from_cert,
     internal_gains_section_from_cert,
+    mean_internal_temperature_section_from_cert,
     solar_gains_section_from_cert,
     ventilation_from_cert,
     water_heating_section_from_cert,
@@ -439,3 +440,81 @@ def test_section_6_line_84_total_gains_match_pdf(
     # Assert
     for m in range(12):
         _pin(actual[m], expected[m], f"§6 (84)[{m+1}] {fixture_name}")
+
+
+# ============================================================================
+# §7 Mean internal temperature — LINE_85..LINE_94 scalar + monthly tuples
+# ============================================================================
+
+_SECTION_7_SCALAR_PINS: Final[tuple[tuple[str, str], ...]] = (
+    ("LINE_85_T_H1_C",          "living_area_heating_temp_c"),
+    ("LINE_91_LIVING_AREA_FRACTION", "living_area_fraction"),
+)
+
+_SECTION_7_MONTHLY_PINS: Final[tuple[tuple[str, str], ...]] = (
+    ("LINE_86_M_UTILISATION_LIVING",     "utilisation_factor_living_monthly"),
+    ("LINE_87_M_MIT_LIVING_C",           "mean_internal_temp_living_monthly"),
+    ("LINE_88_M_T_H2_C",                 "elsewhere_heating_temp_monthly"),
+    ("LINE_89_M_UTILISATION_ELSEWHERE",  "utilisation_factor_elsewhere_monthly"),
+    ("LINE_90_M_MIT_ELSEWHERE_C",        "mean_internal_temp_elsewhere_monthly"),
+    ("LINE_92_M_MIT_C",                  "mean_internal_temp_monthly"),
+    ("LINE_93_M_ADJUSTED_MIT_C",         "adjusted_mean_internal_temp_monthly"),
+    ("LINE_94_M_UTILISATION_WHOLE",      "utilisation_factor_whole_monthly"),
+)
+
+
+@pytest.mark.parametrize(
+    "fixture_name,fixture_attr,result_attr",
+    [
+        (fix, line, attr)
+        for fix in _FIXTURES
+        for line, attr in _SECTION_7_SCALAR_PINS
+    ],
+    ids=lambda x: x if isinstance(x, str) else None,
+)
+def test_section_7_scalar_line_refs_match_pdf(
+    fixture_name: str, fixture_attr: str, result_attr: str
+) -> None:
+    """§7 scalar pins — (85) T_h1 living-area heating temp + (91) living
+    area fraction."""
+    # Arrange
+    mod = _FIXTURES[fixture_name]
+    epc = mod.build_epc()  # type: ignore[attr-defined]
+    expected = getattr(mod, fixture_attr)
+
+    # Act
+    mit = mean_internal_temperature_section_from_cert(epc)
+    assert mit is not None, f"{fixture_name}: mit_from_cert returned None"
+    actual = getattr(mit, result_attr)
+
+    # Assert
+    _pin(actual, expected, f"§7 {fixture_attr} {fixture_name}")
+
+
+@pytest.mark.parametrize(
+    "fixture_name,fixture_attr,result_attr",
+    [
+        (fix, line, attr)
+        for fix in _FIXTURES
+        for line, attr in _SECTION_7_MONTHLY_PINS
+    ],
+    ids=lambda x: x if isinstance(x, str) else None,
+)
+def test_section_7_monthly_line_refs_match_pdf(
+    fixture_name: str, fixture_attr: str, result_attr: str
+) -> None:
+    """§7 monthly pins — every Jan..Dec value of (86)..(94) MIT + η lines
+    matches the U985 PDF to abs=1e-4."""
+    # Arrange
+    mod = _FIXTURES[fixture_name]
+    epc = mod.build_epc()  # type: ignore[attr-defined]
+    expected = getattr(mod, fixture_attr)
+
+    # Act
+    mit = mean_internal_temperature_section_from_cert(epc)
+    assert mit is not None, f"{fixture_name}: mit_from_cert returned None"
+    actual = getattr(mit, result_attr)
+
+    # Assert
+    for m in range(12):
+        _pin(actual[m], expected[m], f"§7 {fixture_attr}[{m+1}] {fixture_name}")