diff --git a/docs_dev/plans/2026-07-31-shelf-c-attribute-shop.md b/docs_dev/plans/2026-07-31-shelf-c-attribute-shop.md
index 371721b..caddae7 100644
--- a/docs_dev/plans/2026-07-31-shelf-c-attribute-shop.md
+++ b/docs_dev/plans/2026-07-31-shelf-c-attribute-shop.md
@@ -371,8 +371,16 @@ func _apply_attr_purchases() -> void:
 			continue
 		var mode: String = String(sp.get("mode", "flat"))
 		var step: float = float(sp.get("step", 0.0))
-		# pct 合并：n 次 +step 在连乘下等价于单条 (1+step)^n − 1
-		var merged: float = (pow(1.0 + step, float(n)) - 1.0) if mode == "pct" else (step * float(n))
+		# pct 合并必须按属性的 combine 分支——AttributeFormula 对 hybrid 用 f=1+v、对 inverse 用 f=1-v，
+		# 故两者的等价单条值不同。写错会让 inverse 属性（cast_delay_mod）的曲线整体偏离且零诊断。
+		var combine: String = String(_attr_def.get(id, {}).get("combine", "hybrid"))
+		var merged: float = 0.0
+		if mode == "pct":
+			# hybrid: 需 f=(1+step)^n → merged=(1+step)^n−1
+			# inverse: 需 f=(1−step)^n → merged=1−(1−step)^n
+			merged = (1.0 - pow(1.0 - step, float(n))) if combine == "inverse" else (pow(1.0 + step, float(n)) - 1.0)
+		else:
+			merged = step * float(n)   # flat 线性可加，与 combine 无关
 		PlayerStats.add_modifier(id, mode, merged, MOD_SOURCE_SHOP_C)
 
 ## 存档：只存次数，加成是派生物（回读时经 _apply_attr_purchases 重建）
diff --git a/docs_dev/specs/2026-07-31-shelf-c-attribute-shop-design.md b/docs_dev/specs/2026-07-31-shelf-c-attribute-shop-design.md
index 05a4d11..94a850f 100644
--- a/docs_dev/specs/2026-07-31-shelf-c-attribute-shop-design.md
+++ b/docs_dev/specs/2026-07-31-shelf-c-attribute-shop-design.md
@@ -180,7 +180,8 @@ for id in _attr_purchases:
     var n: int = _attr_purchases[id]
     if n <= 0: continue
     var sp: Dictionary = <attributes.json[id].shop>
-    var merged: float = (pow(1.0 + step, n) - 1.0) if mode == "pct" else (step * n)
+    # pct 合并须按 combine 分支：AttributeFormula 对 hybrid 用 f=1+v、对 inverse 用 f=1−v
+    var merged: float = (1.0 - pow(1.0 - step, n)) if (mode == "pct" and combine == "inverse")         else ((pow(1.0 + step, n) - 1.0) if mode == "pct" else (step * n))
     PlayerStats.add_modifier(id, mode, merged, MOD_SOURCE_SHOP_C)
 ```