# Handover — post Slices S0380.156..159

Branch: `feature/per-cert-mapper-validation`. **HEAD `fba45d11`**.
Predecessor: [`HANDOVER_POST_S0380_155.md`](HANDOVER_POST_S0380_155.md).

## TL;DR

Four slices landed — three closed the electric 2 (Cat 5 warm-air ASHP
code 524) cohort entry point, one closed the electric 5 (Cat 7
slimline storage code 402 + 18-hour tariff) entry point. All four
came from the same per-line walk discipline: dump the worksheet
section the residual landed in, identify the diverging line ref,
look up the spec rule.

| Slice | Commit | Spec rule closed |
|---|---|---|
| S0380.156 | `02092c80` | SAP 10.2 Table 3 (p.160) zero-loss list — universal WHC=903 guard at top of `_primary_loss_applies`. Cat-4 HP branch was falsely returning True when WHC=903 means electric immersion (no primary circuit). |
| S0380.157 | `a2a4b682` | SAP 10.2 Table 2b note b) (p.159) "×0.9 if separate DHW timing (boiler / warm-air / HP)". Companion WHC=903 guard at top of `_separately_timed_dhw`. Electric immersion is not in the verbatim system-type list. |
| S0380.158 | `8843df1b` | SAP 10.2 Table 4f (p.174) row "Warm air heating system fans" = SFP × 0.4 × V per footnote e default SFP = 1.5 W/(l/s). New `_TABLE_4A_WARM_AIR_SAP_CODES` frozenset (22 codes) + leaf helper. |
| S0380.159 | `fba45d11` | SAP 10.2 Table 4a (p.166) Cat 7 R splits between Off-peak (codes 402/403 R=0.2) and 24-hour heating tariff (R=0.4). Per §12.4.3 the 18-hour tariff has 18h low-rate availability ≈ continuous charging → routes to the 24-hour Table 4a R sub-row for codes 402/403/405/406. |

Extended handover suite at HEAD: **903 pass, 0 fail.** Pyright net-zero
(43 → 43). Σ |ΔSAP_c| across the 25-variant cohort: **2.87 → 1.21**
(58% reduction across 4 slices over one session).

## Disciplines reinforced this session

1. **Per-line walk → spec → fix.** Every closure came from dumping the
   failing variant's worksheet line-by-line:
   - .156: cascade `primary_loss_monthly_kwh_annual = 509.98` vs
     worksheet (59)m = 0 every month → Table 3 zero-loss line.
   - .157: cascade `solar_storage_monthly_kwh_annual = 403.87` vs
     worksheet (56) = 448.73 → ratio = 0.9 exactly → Table 2b note b.
   - .158: cascade `pumps_fans_kwh_per_yr = 0` vs worksheet (249) =
     136.35 → Table 4f warm-air fans = 1.5 × 0.4 × 227.25.
   - .159: cascade T_living = 20.12 vs worksheet 19.6519 → all MIT
     inputs match → back-solve from Tsc formula isolates R as the
     only divergence → Table 4a Cat 7 24-hour sub-row.

2. **Companion WHC=903 fixes.** S0380.156 and .157 both added a guard
   at the **top** of a predicate that already had logic for the same
   case lower down. The Cat-4 HP early-return was masking the
   downstream electric-immersion / electric-water checks. Pattern:
   when a predicate has a per-system-category early-return, the
   data-shape gate (here WHC=903) needs to come **first**.

3. **Spec docstring flagged the gap before it surfaced.** S0380.159
   closed a TODO already noted in the source — the existing
   `_RESPONSIVENESS_BY_SAP_CODE` dict comment said "promote to
   (sap_code, tariff) lookup when 24-hour fixture surfaces; until
   then the off-peak default applies (under-shoots R for the
   24-hour case)." The 18-hour fixture surfaces in this corpus.

## Current residual state at HEAD `fba45d11`

### Cascade-OK tier (25 variants on pin grid)

Sorted by |ΔSAP_c|:

| Variant | ΔSAP_c | Δcost | ΔCO2 | ΔPE | Notes |
|---|---:|---:|---:|---:|---|
| oil 1 | **-0.0000** | **-0.00** | **+0.00** | **+0.00** | EXACT |
| oil pcdb 1 | **+0.0000** | **+0.00** | **-0.00** | **+0.00** | EXACT |
| oil pcdb 2 | **+0.0000** | **+0.00** | **-0.00** | **+0.00** | EXACT |
| oil pcdb 3 | **+0.0000** | **+0.00** | **+0.00** | **-0.00** | EXACT |
| electric 1 | **-0.0000** | **-0.00** | +11.95 | +48.66 | SAP/cost exact, lighting-PE quirk |
| solid fuel 5 | **+0.0000** | **+0.00** | +11.95 | +48.66 | same lighting-PE quirk |
| solid fuel 6 | **+0.0000** | **+0.00** | +11.95 | +48.66 | same |
| solid fuel 7 | **-0.0000** | **+0.00** | +11.95 | +48.66 | same |
| solid fuel 8 | **-0.0000** | **+0.00** | +11.95 | +48.66 | same |
| solid fuel 2 | **-0.0000** | **-0.00** | -93.10 | -1027.51 | SAP/cost exact, §12.4.4 blend artifact |
| solid fuel 3 | **-0.0000** | **-0.00** | +0.00 | -0.00 | EXACT |
| pcdb 1 | -0.0108 | +£0.24 | +1.33 | +5.70 | basically exact |
| gshp | -0.0178 | +£0.41 | +7.06 | +33.52 | basically exact |
| ashp | -0.0240 | +£0.55 | +7.33 | +36.34 | basically exact |
| solid fuel 4 | +0.0850 | -£1.96 | -9.31 | -5.78 | cluster |
| solid fuel 11 | +0.0912 | -£2.10 | +10.55 | -0.74 | cluster |
| electric 8 | +0.0941 | -£2.17 | +7.92 | +6.58 | cluster |
| electric 7 | +0.1017 | -£2.34 | +7.64 | +3.10 | cluster |
| **electric 5** | **+0.1081** | **-£2.49** | **+7.30** | **+0.07** | **CLOSED in .159 — was -1.18** |
| electric 6 | +0.1081 | -£2.49 | +7.32 | +0.16 | cluster |
| solid fuel 9 | +0.1072 | -£2.47 | +9.69 | -5.07 | cluster |
| **electric 2** | **-0.1087** | **+£2.50** | **+16.54** | **+97.69** | **CLOSED in .156-.158 — was -0.46** |
| solid fuel 10 | +0.1134 | -£2.61 | +9.31 | -13.91 | cluster |
| electric 9 | +0.1199 | -£2.76 | +6.82 | -4.51 | cluster |
| electric 3 | +0.1215 | -£2.80 | +6.72 | -5.99 | cluster |

**Σ |ΔSAP_c| = 1.21** (was 2.87 at start of S0380.156).
**Σ |ΔCO2| = 267.67 kg** (was ~310).
**Σ |ΔPE| = 1489.96 kWh** (was ~2400 — driven by 5-variant lighting cluster + sf2).

Buckets:
- **EXACT** (|Δ|<1e-4): **11/25** (44%)
- **basically exact** (|Δ|<0.05): 3/25 (ashp/gshp/pcdb1)
- **mid** (0.05..0.3): 11/25 — the 9-variant cluster (electric 3/5/6/7/8/9 + sf 4/9/10/11) + electric 2
- **big** (>=0.3): **0/25** — all variants now under 0.3 SAP

### Blocked tier (16 variants — `MissingMainFuelType`)

Unchanged. Community heating × 5, electric storage 11-14, no system,
oil 2-6, pcdb 3.

## Open fronts ranked by leverage

### 1. The 9-variant cluster — ±0.09..0.13 SAP / −£2..−£3 / +£7 CO2 / small PE

electric 3, electric 5, electric 6, electric 7, electric 8, electric 9,
solid fuel 4, solid fuel 9, solid fuel 10, solid fuel 11 — plus
similar magnitudes on electric 5 post-.159.

The pattern is uniform:
- ΔSAP +0.085 .. +0.121 (always positive — cascade SAP higher than worksheet)
- Δcost −£1.96 .. −£2.80 (cascade cost lower — under-charging by ~38 kWh × 7.41 p/kWh)
- ΔCO2 +6.72 .. +10.55 kg (cascade over-emitting)
- ΔPE −13.91 .. +6.58 kWh (small, both signs)

The cost gap is consistent with cascade SH demand being **~38 kWh
lower** than worksheet. Diagnostic from earlier probing on electric
3 / 6: cascade SH_demand ≈ 11050 vs worksheet (98c) ≈ 11088 (diff
−38 kWh per variant).

**Hypothesis (per [[feedback-spec-floor-skepticism]] — verify before
accepting)**: prior handover ranked this cluster as "lowest leverage —
probably Elmhurst-vs-spec PE/CO2 monthly factor pattern". After .159
closed electric 5 from ALSO being in this pattern, that hypothesis
looks weaker — the same cluster shape may have a clean spec citation.
Suggested probe:
- Pick one cluster variant (electric 3 or solid fuel 4) and run a
  per-line walk against the worksheet (98c)/(211)/(255).
- The −£2.50 cost suggests **38 kWh SH demand difference**. Where?
- Check §8 step 10 `Qheat = 0.024 × (Lm − η·Gm) × nm` line refs vs
  worksheet (98a). If cascade Qheat is off, look upstream at (97).
- Closing this cluster would shave **Σ|ΔSAP| from 1.21 → ~0.10** in
  one slice. **Highest leverage today.**

### 2. Electric 2 follow-up — −0.11 SAP / +£2.50 cost / +£16 CO2 / +£98 PE

Cascade now overshoots after .156-.158 wired the missing
primary-loss / storage-loss / warm-air-fan components correctly.
Likely a small upstream SH cascade gap (cascade SH demand +57 kWh
over worksheet — Cat 5 warm-air HP specific). The +136 kWh warm-air
fan electricity bills at 18-hour high rate → adds £18.64 + 18.54 kg
CO2 + 204 kWh PE. The over-shoot of +£2.50 / +£16 CO2 / +£98 PE
roughly matches the magnitude → suggests one of:
- The warm-air fan should bill at a different rate (Table 12a
  fraction for ALL_OTHER_USES on 18-hour vs the Appendix F2 rate).
- The fan power should be lower for Cat 5 HPs (different SFP than
  the default 1.5 W/(l/s)).
- Some other small Cat 5 / warm-air HP specific rule.

**Suggested probe**: dump the worksheet (249) cost line carefully —
worksheet shows 136.35 × 13.67 = £18.64. Cascade should compute the
same. If Δcost ≠ +£18.64, then the fan kWh is right but the rate is
not. If Δcost = +£18.64, the fan kWh shouldn't be there at all on
this row (maybe it goes to a different (249)b line).

### 3. Lighting-only PE +48.66 cohort — 5 variants — **DEFERRED**

electric 1, solid fuel 5/6/7/8. SAP/cost EXACT; PE +48.66 / CO2
+11.95 from Elmhurst using Table 12 ANNUAL factor for off-peak HW
immersion split. Spec Table 12d/12e header mandates MONTHLY factors.
Closing it violates spec.

### 4. Mapper-extension unblocking (16 blocked variants)

- Community heating × 5 — extend extractor for §14.1 block.
- Electric storage 11-14 — extend `_ELMHURST_MAIN_HEATING_EES_TO_FUEL_CODE`
  for EES codes WEA, REA, OEA.
- "No system" — spec-assumed direct electric.
- Oil 2-6 — Table 4b non-oil liquid fuels (HVO/FAME/B30K/bioethanol).
- pcdb 3 — `"Bulk LPG"` mapper dict gap.

Separate from cascade closure work. Each unblock = one mapper slice.

## Slice history (this session)

| Slice | HEAD | Scope |
|---|---|---|
| S0380.156 | `02092c80` | SAP 10.2 Table 3 (PDF p.160) zero-loss list — universal WHC=903 guard at the top of `_primary_loss_applies`. New `_WHC_ELECTRIC_IMMERSION: Final[int] = 903` constant. Pre-slice the Cat 4 HP branch returned True unconditionally when no PCDB record was lodged → electric 2 cascade falsely added ~510 kWh/yr primary loss. Closures electric 2: HW kWh 2849 → 2339, ΔSAP −0.46 → +0.81 (residual swung past — exposed offsetting bugs). Δcost +£10.56 → −£18.71, ΔPE +443 → −162. |
| S0380.157 | `a2a4b682` | SAP 10.2 Table 2b note b) (PDF p.159) — companion WHC=903 guard at top of `_separately_timed_dhw`. Pre-slice the Cat 4 HP branch fired before the existing `_is_electric_water` check could route to False; cascade applied ×0.9 to (53) Temperature Factor on an immersion-fed cylinder. Reuses `_WHC_ELECTRIC_IMMERSION`. Closures electric 2: storage loss 403.87 → 448.73 EXACT, HW kWh 2339 → 2384.12 EXACT match worksheet, ΔSAP +0.81 → +0.70. |
| S0380.158 | `8843df1b` | SAP 10.2 Table 4f (PDF p.174) row "Warm air heating system fans" = SFP × 0.4 × V per footnote e default SFP = 1.5 W/(l/s). New `_TABLE_4A_WARM_AIR_SAP_CODES` frozenset (22 codes: Cat 5 HPs 521/523-527 + Cat 9 warm-air 501-515/520) + leaf helper `_table_4f_warm_air_heating_fans_kwh(main, dwelling_volume_m3, has_balanced_mv)`. Footnote-e balanced-MV omission via `_has_balanced_mechanical_ventilation` predicate. Closures electric 2: pumps_fans 0 → 136.35 EXACT, ΔSAP +0.70 → −0.11, Δcost −£16.14 → +£2.50. |
| S0380.159 | `fba45d11` | SAP 10.2 Table 4a (PDF p.166) Cat 7 R splits Off-peak vs 24-hour heating tariff sub-rows. Per §12.4.3 the 18-hour tariff has 18h low-rate availability ≈ continuous charging. New `_CONTINUOUS_CHARGING_TARIFFS = {EIGHTEEN_HOUR, TWENTY_FOUR_HOUR}` + `_RESPONSIVENESS_24_HOUR_OVERRIDE_BY_SAP_CODE` (codes 402/403/405/406). `tariff: Optional[Tariff]` parameter added to `_responsiveness`; threaded through both MIT cascade call sites. Closures electric 5: ΔSAP −1.18 → +0.11 (91% reduction), Δcost +£27.09 → −£2.49, ΔPE +438 → +0.07 EXACT. Electric 5 now joins the 9-variant cluster pattern. |

## Standard slice workflow (unchanged)

1. Read spec page + identify rule
2. Probe one cluster variant; verify diagnosis via monkey-patch / direct walk
3. Write failing AAA test (literal `# Arrange / # Act / # Assert`)
4. Implement helper / dispatch entry / mapper extension
5. Re-pin affected variants (DO NOT widen tolerance)
6. Run extended handover suite (command below)
7. Pyright net-zero check (`git stash` → pyright → `git stash pop` → pyright)
8. Commit with spec citation + `Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>`
9. Update `project-heating-systems-corpus` + `MEMORY.md` index

## Test baseline at HEAD `fba45d11`

```bash
PYTHONPATH=/workspaces/model python -m pytest \
    backend/documents_parser/tests/test_summary_pdf_mapper_chain.py \
    backend/documents_parser/tests/test_heating_systems_corpus.py \
    backend/documents_parser/tests/test_elmhurst_extractor.py \
    backend/documents_parser/tests/test_elmhurst_end_to_end.py \
    domain/sap10_calculator/worksheet/tests/test_e2e_elmhurst_sap_score.py \
    domain/sap10_calculator/worksheet/tests/test_heat_transmission.py \
    domain/sap10_calculator/worksheet/tests/test_internal_gains.py \
    domain/sap10_calculator/worksheet/tests/test_solar_gains.py \
    domain/sap10_calculator/worksheet/tests/test_dimensions.py \
    domain/sap10_calculator/worksheet/tests/test_rating.py \
    domain/sap10_calculator/worksheet/tests/test_ventilation.py \
    domain/sap10_calculator/worksheet/tests/test_appendix_h_solar.py \
    domain/sap10_calculator/worksheet/tests/test_mev.py \
    domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py \
    domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py \
    domain/sap10_calculator/tests/test_pcdb_table_322_lookup.py \
    domain/sap10_calculator/tests/test_pcdb_table_329_lookup.py \
    domain/sap10_calculator/tests/test_table_12a.py \
    --no-cov -q
```

Expected: **903 pass, 0 fail.**

## Memories to load (in order)

```
project-heating-systems-corpus            # HEAD fba45d11
feedback-sap-10-2-only-never-10-3         # CRITICAL — never reference SAP 10.3
feedback-software-no-special-handling     # CRITICAL — apply spec uniformly
feedback-spec-floor-skepticism            # CUTS BOTH WAYS — skeptical of your OWN audit narrative
feedback-worksheet-not-api-reference
feedback-spec-citation-in-commits
feedback-verify-handover-claims
feedback-zero-error-strict                # TARGET: ΔSAP_c < 1e-4 vs worksheet
feedback-commit-per-slice
feedback-aaa-test-convention
feedback-e2e-validation-philosophy
feedback-abs-diff-over-pytest-approx
feedback-golden-residuals-near-zero
feedback-one-e-minus-4-across-the-board
reference-unmapped-sap-code
reference-unmapped-api-code
project-oil-price-spec-divergence
```

## What NOT to do

- **Don't reference SAP 10.3** — track 10.2 deliberately.
- **Don't widen pin tolerances** — re-pin smaller or find the spec gap.
- **Don't add empirical gates** to keep cohort pins stable when a
  spec rule clearly applies.
- **Don't re-investigate Slices .91..159** — all settled.
- **Don't add new helpers to `domain/sap10_ml/`** — on deprecation
  path; `domain/sap10_calculator/tables/` is the canonical home.
- **Don't treat ΔSAP=0.07 as "closed"** — target is <1e-4 vs worksheet.
- **Don't try to close the lighting-PE +48.66 cluster** — it's an
  Elmhurst-vs-spec quirk that closing would violate spec.
- **Don't form a spec hypothesis without per-line data** — walk the
  worksheet line-by-line for the failing variant first.

## Spec source quick-reference

All under `domain/sap10_calculator/docs/specs/`:

- **SAP 10.2 full spec**: `sap-10-2-full-specification-2025-03-14.pdf`
  - **§4** (p.135-137) — water heating worksheet (45..65)
  - **§7** (p.26) — Mean internal temperature
  - **§9.2.4** (p.27) — Solid fuel boiler systems
  - **§9.4.11** (p.30) — Boiler interlock: -5pp to BOTH SH and DHW
  - **§9.4.19** (p.34-35) — Storage heater controls
  - **§12.4.3** (p.36) — Electric tariff types (7-hour / 10-hour /
    18-hour / 24-hour heating). **Slice .159.**
  - **§12.4.4** (p.36-37) — Solid fuel back-boiler summer immersion.
    **Slice .154.**
  - **§A.2.2** (~p.189) — Forced-secondary set
  - **Appendix D §D2.1 (2)** (p.57) — Eq D1 monthly water eff cascade
  - **Appendix F2** (p.63) — 18-hour CPSU
  - **Appendix N3** (p.107-109) — Heat pump DHW efficiency cascade
  - **Table 2b** (p.159) — Cylinder temperature factor + note b ×0.9
    rule for boiler/warm-air/HP. **Slice .157.**
  - **Table 3** (p.160) — Primary circuit loss; zero-loss list incl.
    electric immersion. **Slices .152 / .153 / .156.**
  - **Table 4a** (p.163-170) — heating systems + R splits between
    Off-peak and 24-hour heating tariff for Cat 7 electric storage.
    **Slices .155 / .159.**
  - **Table 4b** (p.168) — gas/liquid boilers seasonal efficiency
  - **Table 4e** (p.171-173) — heating system controls + temperature
    adjustment column. Group 4 storage controls 2401/2402/2403.
  - **Table 4f** (p.174) — pumps + fans (incl. warm-air row).
    **Slice .158.**
  - **Tables 9 / 9a / 9b / 9c** (p.182-184) — heating periods, MIT
    cascade, T_sc formula. Used in .159 back-solve.
  - **Table 11** (p.188) — secondary heating fraction
  - **Table 12** (p.191) — SAP rating fuel prices + standing charges
  - **Table 12a** (p.191) — high/low-rate fraction by system × tariff
  - **Table 12d/12e** (p.195-196) — monthly variation in CO2/PE factors
  - **Table 13** (p.197) — high-rate fraction for electric DHW
- **RdSAP 10 spec**: `RdSAP 10 Specification 10-06-2025.pdf`
  - **§4.1 Table 5** (p.28) — Ventilation parameters
  - **§5** (p.29) — Floor infiltration spec rule
  - **§10.11 Table 29** (p.56) — Heating/HW parameters
  - **§19 Table 32** (p.95) — RdSAP10 fuel prices / CO2 / PE

## Good luck.