Publish a half-point SAP rating rounded up 🟩

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

domain/sap10_calculator/worksheet/rating.py

@@ -20,6 +20,7 @@ Table 12 (page 191).
 
 from __future__ import annotations
 
+from decimal import ROUND_HALF_UP, Decimal
 from math import log10
 from typing import Final
 
@@ -59,8 +60,14 @@ def sap_rating_integer(*, ecf: float) -> int:
     """SAP 10.2 §13: round the continuous SAP rating to the nearest integer
     and clamp to a minimum of 1 ("if the result of the calculation is less
     than 1 the rating should be quoted as 1"). The integer value is the
-    one published on the EPC."""
-    return max(1, round(sap_rating(ecf=ecf)))
+    one published on the EPC.
+
+    "Nearest" is half-UP, as everywhere else the spec rounds (see the mapper's
+    `_round_half_up_2dp`). Python's built-in `round` is half-to-EVEN and would
+    drop an exact x.5 to x for even x — at a band floor that publishes a whole
+    band low (a continuous 68.5 as SAP 68 / band D rather than 69 / band C)."""
+    rating: Decimal = Decimal(sap_rating(ecf=ecf))
+    return max(1, int(rating.quantize(Decimal("1"), rounding=ROUND_HALF_UP)))
 
 
 def environmental_impact_rating(