Model/domain/sap10_calculator/docs/HANDOVER_POST_S0380_200.md

Handover — post S0380.200 (dual-main split done; boiler-interlock −5pp OPEN)

Point-in-time note. Start from AGENT_GUIDE.md for methodology, accuracy bar, and pipeline — this records what this session did and what is open.

• Branch: feature/per-cert-mapper-validation
• HEAD: 8ae978a6 (S0380.200)
• Baseline: 2355 passed, 1 skipped, 0 failed. Verify with the AGENT_GUIDE §4 suite command.

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What this session shipped (S0380.196–200)

The through-line: golden certs 6035 and 0240 were both closed to SAP-exact by finding real API-mapper bugs (not "lodged divergence"), each confirmed against a user-generated Elmhurst worksheet ("simulated case 5/6").

Slice	What	Spec
.196	API Simplified Type 1 room-in-roof: room_in_roof_type_1 gables (length-only, no height) weren't deducted from the A_RR shell → whole shell billed as roof at U_RR=2.30 (+52 W/K). Route them through detailed_surfaces (gable area = L × 2.45 default RR storey height). 6035 SAP −2→+0 exact, PE +19.16→+1.84.	RdSAP 10 §3.9.1(e) p.21; Table 4 p.22
.197	Promoted "simulated case 5" (detached sandstone RR) to e2e fixture (001431_case5, 11 pins @1e-4). Fixed sandstone wall label "SS"→2 (_ELMHURST_WALL_CODE_TO_SAP10) + _parse_thickness_mm for "400+ mm" roof insulation (trailing + was dropped → u_roof fell to age default).	—
.198	API window_wall_type=4 → roof window. These are roof-of-room rooflights; the mapper flattened them into sap_windows (vertical, (27), U=2.0) instead of sap_roof_windows ((27a), inclined U=2.30 + 45° solar). The inclined solar dominates → 0240 SAP −1→+0 exact, PE +3.91→+1.95; 6035 PE +1.84→+1.37. Discriminator is wall_type==4 NOT window_type==2 (0390/7536 lodge window_type=2 on main walls).	SAP 10.2 §3 (27a); Table 6e Note 2
.199	Site-notes mirror of .198: extractor parses "Roof of Room" window rows (_parse_window_from_anchors); _is_elmhurst_roof_window location branch; _ELMHURST_ROOF_WINDOW_U_BY_GLAZING["Double between 2002 and 2021"]=2.30. Case 6 pinned on §3 windows (test_section_3_roof_windows_case6_match_pdf): (27)=22.7408, (27a)=13.0375 exact.	RdSAP 10 §3.7
.200	SAP 10.2 §9a two-main-heating split (203)/(204)/(205)/(207)/(213). The cascade lumped a 2-main dwelling into one system. Now space_heating_fuel_monthly_kwh splits demand (204) to sys1 @ (206) + (205) to sys2 @ (207); _solve_month sums main_1+main_2; _main_heating_detail_efficiency (new, the per-detail core of _main_heating_efficiency) gives each system its own efficiency. Site-notes: _map_elmhurst_main_heating_2 inherits Main 1's fuel when §14.1 omits Fuel Type. Cost/CO2/PE main_2 paths were already wired. 0240 unchanged (identical Eq-D1 systems).	SAP 10.2 §9a

Two new e2e fixtures: 001431_case5 (full SapResult, S0380.197) and 001431_case6 (§3 windows only, S0380.199 — see why below). Source PDFs tracked under sap worksheets/golden fixture debugging/simulated case {5,6}/; Summaries mirrored to backend/documents_parser/tests/fixtures/Summary_001431_case{5,6}.pdf.

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⚠️ CORRECTION (post S0380.201) — the interlock priority was ALREADY DONE

The "priority" below was misdiagnosed. At HEAD the cascade already produces case 6 (206) sys-1 eff = 79.0 and (207) sys-2 eff = 84.0, matching the worksheet exactly. The cylinder-thermostat interlock path (no_stored_hw_interlock = has_cylinder and cylinder_thermostat != "Y") has existed since S0380.141; the room-thermostat path since S0380.177. no_interlock = no_room_thermostat OR no_stored_hw_interlock — it does NOT only catch 2101/2102. Toggling case 6 cylinder_thermostat N→Y flips eff 0.79→0.84, confirming the −5pp fires. Golden 0240 is a combi (has_hot_water_cylinder=False) → correctly NOT penalised; its predicted re-pin from the interlock is void. The misread came from energy_requirements_section_from_cert (a §2.4 debug helper using raw _main_heating_efficiency, which reports 84 — the real cert_to_inputs cascade applies the −5pp at ~line 6071). See feedback-verify-handover-claims.

S0380.201 landed the SECONDARY item (dual-system aux pumps): SAP 10.2 Table 4f note c) second main-system circulation pump, gated on a lodged main_heating_fraction > 0. Case 6 (231) 241 → 356 EXACT (= 41 Main-1 pump + 115 Main-2 pump + 200 oil aux). 0240 re-pinned (pumps 315 → 430, integer 73 → 72, resid +0 → -1, PE +2.8092, CO2 +0.1385) — anticipated and authorised below. 000565 protected by the fraction>0 gate (its Main 2 is a DHW-only combi, fraction 0).

Remaining case-6 gaps for full-SapResult promotion (vs P960-0001-001431):

• (98c) space demand cascade 12145.31 vs ws 11991.96 (+1.28%) — living-area MIT (87) ~0.3 °C low in winter; multi-causal (gains/heat-loss).
• (219) hot water cascade 4824.74 vs ws 4902.86 (−1.6%) — §4 walk needed. Once both close, promote case 6 to a full SapResult e2e fixture (pin grid below).

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OPEN (was the priority, now DONE) — boiler-interlock −5pp efficiency adjustment, per main system

Goal: a RdSAP-10/SAP-10.2 spec-accurate implementation of the boiler interlock efficiency adjustment, applied per main heating system, done in the established pattern of this domain (per-line walk → cite spec → TDD → re-pin). This is the last gap blocking full closure of simulated case 6, and it will also re-pin golden 0240.

The evidence (simulated case 6)

sap worksheets/golden fixture debugging/simulated case 6/ — detached, dual oil boiler (both SAP code 127, base seasonal eff 84%), radiators 51% (control 2106) + underfloor 49% (control 2110). Its P960 worksheet:

line	worksheet	meaning
(206) main sys-1 eff	79.0	84 − 5pp
(207) main sys-2 eff	84.0	base, no penalty
(216) water-heater eff	72.0	also penalised (DHW leg of the −5pp)
"Temperature adjustment"	0.0000	flow temp has NO effect — this is NOT a flow-temperature feature

Summary §14 lodges it explicitly: system 1 "Boiler Interlock: No", system 2 "Boiler Interlock: Yes". The 84→79 is the SAP 10.2 Table 4c(2) "no boiler interlock" −5pp Space + DHW adjustment (same mechanism as the AGENT_GUIDE "oil 6" worked example, S0380.177 — but that one fired off control 2101).

Why control 2106 (which HAS a room thermostat) is "no interlock"

Per RdSAP 10 boiler-interlock rules (find + cite the exact §; the existing _NO_INTERLOCK_CONTROLS = {2101, 2102} block in cert_to_inputs.py ~line 1238 quotes "RdSAP 10 §3 p.57: boiler interlock is assumed present if there is a room thermostat and [time control], AND — when there is a hot-water cylinder — a cylinder thermostat; otherwise not interlocked"): system 1 serves the DHW cylinder, the cylinder is present (Hot Water Cylinder Present: Yes) but Cylinder Thermostat: No → interlock not present → −5pp, despite the room thermostat. System 2 (underfloor, separate part, no cylinder interaction) keeps interlock via its zone control → no penalty.

So the determination is not "control ∈ {2101,2102}". It is, per system: interlock present ⇔ (room thermostat present, from the control code) AND (time/programmer control) AND (cylinder absent OR cylinder thermostat present). The current cascade only catches the "no room thermostat" path (2101/2102); it misses the "room thermostat present but no cylinder thermostat" path that 2106 hits here.

This single root cause explains BOTH remaining case-6 deltas

• space heating: sys-1 eff 79 not 84 → main fuel cascade 14925 vs ws 14736.96
• hot water: the −5pp DHW leg → cascade HW 4824 vs ws 4902.86 (lower cascade fuel ⇒ cascade eff too high ⇒ missing the penalty)

0240 will shift — and that is correct (apply the spec uniformly)

Golden 0240 has the SAME controls (sys1 2106 / sys2 2110) AND the same cylinder_thermostat = "N" with a cylinder present. So the spec-correct rule applies the −5pp to 0240's system 1 too. 0240 is currently SAP-exact (continuous 72.55) without the penalty — that is an offsetting coincidence (it's API-only, ±0.5 bar, no worksheet). Per feedback-software-no-special-handling + feedback-spec-floor-skepticism: implement the spec rule, let 0240 shift, and re-pin it with a documented note. Expect 0240 continuous SAP to drop ~0.3–0.5 (may take the integer 73→72; if so the golden expected_sap_resid moves −1 and that is the new truth). Measure precisely and re-pin PE/CO2 too.

Where to implement (per-line walk first, then TDD)

1. Interlock determination. Add a per-MainHeatingDetail helper, e.g. _boiler_interlock_present(main, epc) -> bool, encoding the RdSAP 10 rule above (room thermostat from control code + cylinder-thermostat gate when a cylinder is present). epc.sap_heating.cylinder_thermostat ("Y"/"N") and cylinder_size/hot_water_cylinder_present are the cylinder signals. The site-notes path already lodges cylinder_thermostat (mapper.py ~5183, string "Y"/"N"); the API path lodges it on sap_heating.cylinder_thermostat (0240 = "N").
2. Apply Table 4c(2) −5pp per system. The existing −5pp lives near the _NO_INTERLOCK_CONTROLS block — find how it currently adjusts the seasonal efficiency for 2101/2102 and generalise it to fire on not _boiler_interlock_present(main, epc), applied inside _main_heating_detail_efficiency so each main system gets its own adjustment (sys1 −5, sys2 0). Confirm the DHW leg (water-heater efficiency (216)) is penalised too — the §4 water-heating cascade reads _main_heating_efficiency; verify the −5pp flows there (case 6 (216)=72 is the check).
3. Verify combi vs regular rows of Table 4c(2). The "no interlock" −5pp has a combi row (Space −5 / DHW 0) and a regular-boiler row (Space −5 / DHW −5); the DHW leg is gated on cylinder presence. Case 6 is a regular oil boiler with a cylinder → DHW −5 applies (hence (216)=72). Read the table; don't assume.

Validation target

After the fix, promote case 6 to a full SapResult e2e fixture (it's currently §3-windows-only because the lumped efficiency made (211)/(219)/(231) non- comparable). Case 6 worksheet Block-1 pin grid (P960-0001-001431):

• SAP 72 (258), continuous 71.6597, ECF 2.0316 (257)
• total fuel cost 1162.5374 (255), CO2 5953.6679 (272)
• (211) main sys-1 fuel 7741.6458, (213) main sys-2 fuel 6995.3106 (SapResult.main_heating_fuel_kwh_per_yr should be the sum 14736.9564)
• hot water 4902.8601 (219), lighting 357.6571 (232)
• pumps/fans 356.0 (231) — see the SECOND open item below

SECONDARY open item — dual-system auxiliary pumps (Table 4f)

Case 6 (231) = 356 = (230c) central-heating pump 156 + (230d) oil-boiler pump 200. Cascade gives 241. Two boilers → two pump contributions per Table 4f (note c: "where there are two main heating systems include two figures from this table" — same note already used for the 0240 oil-pump in S0380.148). Needs the per-system pump aggregation. Smaller than the interlock fix; do it after, then case 6's (231) pin closes and the full e2e fixture lands.

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Process notes

• One slice = one commit, spec citation (page + line) in the message, Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> trailer.
• AAA tests (# Arrange/# Act/# Assert), abs(x-y) <= tol (not pytest.approx).
• New code passes pyright strict, 0 errors. (mapper.py + cert_to_inputs.py each carry 32 pre-existing errors — don't add to them; check with a git stash baseline comparison.)
• The Elmhurst worksheet is ground truth at abs=1e-4. 0240 is API-only (±0.5 fallback) — case 6 is its worksheet-backed proxy for the heating archetype, but differs from 0240 on the boiler SAP code (127 vs 0240's 130 condensing combi), so pin case 6 to ITS OWN worksheet, not 0240's register.
• Suite command + section/e2e harness layout: AGENT_GUIDE §2.6 + §4.