fix: 企微审批选填附件控件为空列表时跳过，避免非客户收款退款提交失败

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/infrastructure/wecom/approval_form.go

@@ -101,7 +101,7 @@ func buildApprovalForm(ctx context.Context, businessType string, applicationID,
 	attachmentCount := 0
 	for _, mapping := range mappings {
 		raw, exists := lookupSnapshotValue(snapshot, mapping.BusinessField)
-		if !exists || raw == nil {
+		if !exists || raw == nil || isEmptyFileValue(mapping, raw) {
 			if requiredControls[mapping.ControlID] {
 				return approvalFormBuildResult{}, errors.New(errors.CodeInvalidStatus, "审批业务快照缺少模板必填字段: "+mapping.BusinessField)
 			}
@@ -125,6 +125,23 @@ func buildApprovalForm(ctx context.Context, businessType string, applicationID,
 	return approvalFormBuildResult{Contents: contents}, nil
 }
 
+// isEmptyFileValue 判断附件控件的快照值是否为空列表；空列表按未填写处理，由模板必填与业务必填规则决定是否拦截。
+func isEmptyFileValue(mapping dto.WeComControlMappingItem, raw any) bool {
+	if !strings.EqualFold(strings.TrimSpace(mapping.ControlType), "file") {
+		return false
+	}
+	switch value := raw.(type) {
+	case []any:
+		return len(value) == 0
+	case []string:
+		return len(value) == 0
+	case string:
+		return strings.TrimSpace(value) == ""
+	default:
+		return false
+	}
+}
+
 // lookupSnapshotValue 支持用点分路径读取嵌套业务快照，避免模板映射绑定具体 DTO。
 func lookupSnapshotValue(snapshot map[string]any, path string) (any, bool) {
 	segments := strings.Split(strings.TrimSpace(path), ".")