fix(billing): 修正模型计费配置继承优先级

apps/api/internal/store/billing_config.go

@@ -0,0 +1,28 @@
+package store
+
+// EffectiveBillingConfigInput describes the billing layers used by runtime and
+// catalog responses. LegacyPlatformModelConfig is retained only as a fallback
+// for models that do not have an effective pricing rule set.
+type EffectiveBillingConfigInput struct {
+	BaseConfig                map[string]any
+	LegacyPlatformModelConfig map[string]any
+	InheritedRuleSetConfig    map[string]any
+	ModelRuleSetConfig        map[string]any
+	Override                  map[string]any
+}
+
+// ResolveEffectiveBillingConfig keeps inherited pricing rules authoritative over
+// the legacy materialized snapshot. Explicit model rules and overrides retain
+// their higher-priority exception semantics.
+func ResolveEffectiveBillingConfig(input EffectiveBillingConfigInput) map[string]any {
+	config := mergeObjects(input.BaseConfig, nil)
+	if len(input.InheritedRuleSetConfig) > 0 {
+		config = mergeObjects(input.InheritedRuleSetConfig, nil)
+	} else if len(input.LegacyPlatformModelConfig) > 0 {
+		config = mergeObjects(input.LegacyPlatformModelConfig, nil)
+	}
+	if len(input.ModelRuleSetConfig) > 0 {
+		config = mergeObjects(input.ModelRuleSetConfig, nil)
+	}
+	return mergeObjects(config, input.Override)
+}