fix: V564 computeRovn 区分 return_n_uv 缺失 vs 0

之前把 returnNuv=null 和 returnNuv=0 都当成 period 缺失,
让另一时段兜底 → 高估"短期表现差"的 vid 粗排分。

修复:
  - exp null/≤0  → period 无效 (period anchor, 保持)
  - returnNuv null → 视为 0 (与 FeatureV6.getOneInfo 同口径)
  - returnNuv = 0 → rovn=0, 参与加权 (真实信号"无回访")

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

recommend-server-service/src/main/java/com/tzld/piaoquan/recommend/server/service/rank/strategy/RankStrategy4RegionMergeModelV564.java

@@ -375,12 +375,18 @@ public class RankStrategy4RegionMergeModelV564 extends RankStrategy4RegionMergeM
         return result;
     }
 
-    /** 与 FeatureV6.oneTypeStatFeature 同口径：rovn = plusSmooth(return_n_uv, exp, plus, 1) */
+    /**
+     * 与 FeatureV6.oneTypeStatFeature 同口径：rovn = plusSmooth(return_n_uv, exp, plus, 1)
+     *
+     * 字段语义（区分 0 vs null）：
+     *   - exp 是 period 有效性 anchor：null 或 ≤0 → 整个 period 无效（return null）
+     *   - return_n_uv 缺失视为 0（真实信号"无回访"）：rovn=0，参与加权（不会让另一时段兜底）
+     */
     private static Double computeRovn(Map<String, String> row, String period, double smoothPlus) {
         Double exp = parseDoubleOrNull(row.get("exp_" + period));
+        if (exp == null || exp <= 0) return null;
         Double returnNuv = parseDoubleOrNull(row.get("return_n_uv_" + period));
-        if (exp == null || exp <= 0 || returnNuv == null || returnNuv <= 0) return null;
-        return FeatureUtils.plusSmooth(returnNuv, exp, smoothPlus, 1);
+        return FeatureUtils.plusSmooth(returnNuv != null ? returnNuv : 0, exp, smoothPlus, 1);
     }
 
     private static Double parseDoubleOrNull(String s) {