A community override keeps an assessor-observed Group 3 control 🟥

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/domain/epc/test_main_heating_system_overlay.py

@@ -647,6 +647,51 @@ def test_unresolvable_or_unmodelled_heating_produces_no_overlay(
     assert simulation is None
 
 
+def test_community_override_keeps_an_observed_group_3_control() -> None:
+    # A community override on a cert that ALREADY lodges community heating is a
+    # confirmation, not a system switch — the assessor observed the control
+    # (e.g. 2306, "charging linked to use, programmer and TRVs", worth ~1-2 SAP
+    # over the flat-rate default). Stamping the 2313 default over it would
+    # destroy real information, so the overlay opts into keeping an existing
+    # Table 4e GROUP 3 control (the heat-network mirror of
+    # `keep_existing_off_peak_meter`, ADR-0053).
+    # Arrange — a cert lodging community heating with an observed 2306.
+    baseline = build_epc()
+    main = baseline.sap_heating.main_heating_details[0]
+    main.sap_main_heating_code = 301
+    main.main_heating_category = 6
+    main.main_heating_control = 2306
+    overlay = main_heating_overlay_for("Community heating, boilers", 0)
+    assert overlay is not None
+
+    # Act
+    result = apply_simulations(baseline, [overlay])
+
+    # Assert — the observed usage-linked control survives.
+    assert result.sap_heating.main_heating_details[0].main_heating_control == 2306
+
+
+def test_community_override_replaces_a_cross_family_control() -> None:
+    # When the replaced system was a DIFFERENT family, its control is stale by
+    # definition — a Group-1 boiler zone control (2110) has no meaning on a
+    # heat network (two live portfolio-796 dwellings carried exactly that) —
+    # so the Group 3 default is stamped (ADR-0053).
+    # Arrange — a cert lodging a gas boiler with zone control.
+    baseline = build_epc()
+    main = baseline.sap_heating.main_heating_details[0]
+    main.sap_main_heating_code = 102
+    main.main_heating_category = 2
+    main.main_heating_control = 2110
+    overlay = main_heating_overlay_for("Community heating, boilers", 0)
+    assert overlay is not None
+
+    # Act
+    result = apply_simulations(baseline, [overlay])
+
+    # Assert — the stale boiler control is replaced by the Group 3 default.
+    assert result.sap_heating.main_heating_details[0].main_heating_control == 2313
+
+
 def test_main_heating_override_remaps_the_primary_system_code() -> None:
     # Arrange
     baseline = build_epc()