fix(kpi): suggest 保留历史默认口径 middle_best — 修复未知编码被误判为 higher_better（C_REBATE_RATE/BH_SALES_10 建议退化） (project-20260911-threshold-fix)

backend/tests/test_threshold_parser.py

@@ -185,6 +185,34 @@ class TestSuggestFormat:
         for level in ("green", "yellow", "red"):
             assert is_valid_threshold(s2[level]["label"]), s2[level]["label"]
 
+    def test_kpi_type_default_preserves_legacy_middle_best(self):
+        """_kpi_type 默认分支必须保持历史语义 = middle_best（原实现的 else 分支）。"""
+        from app.api.thresholds import _kpi_type
+
+        class K:
+            def __init__(self, code):
+                self.kpi_code = code
+
+        assert _kpi_type(K("SALES_TOTAL")) == "higher_better"
+        assert _kpi_type(K("COST_CONTROL_RATE")) == "lower_better"
+        assert _kpi_type(K("C_REBATE_RATE")) == "middle_best"      # 渠补率：历史为适中型
+        assert _kpi_type(K("BH_SALES_10")) == "middle_best"        # 销售-任富海：历史为适中型
+        assert _kpi_type(K("MADE_UP_CODE")) == "middle_best"       # 未知编码 → 默认适中型
+
+    def test_c_rebate_rate_suggestion_is_middle_best_range(self):
+        """回归：C_REBATE_RATE 建议仍走适中型区间口径（不得退化为更高的单边界）。"""
+        from app.api.thresholds import _kpi_type, build_suggestion
+
+        class K:
+            kpi_code = "C_REBATE_RATE"
+
+        t = _kpi_type(K())
+        s = build_suggestion(t, 80.0, tolerance=27.67)
+        assert t == "middle_best"
+        assert s["green"]["label"] == "52.33~107.67"
+        assert is_valid_threshold(s["yellow"]["label"])
+        assert is_valid_threshold(s["red"]["label"])
+
     def test_middle_best_zero_tolerance_guard(self):
         """容忍度退化时不得生成 A~A 之类不可用表达式"""
         s = build_suggestion("middle_best", 0.0, tolerance=0.0)