完善合同气瓶绑定约束与候选过滤

- 明确合同状态、气瓶归属、停用、报废和重复绑定失败原因
- 根据当前合同过滤可绑定气瓶，排除无效及重复候选项
- 从合同列表进入绑定页时锁定预填合同，防止切换上下文
- 切换通用新建页合同后清空旧气瓶并重新加载候选项
- 增加前后端回归检查并同步中文操作日志

backend/api/internal/logic/platform/gasorder/contract_change_error_test.go

@@ -27,6 +27,22 @@ func TestContractChangeBusinessErrors(t *testing.T) {
 	}
 }
 
+// TestContractBindingErrorMessages 验证绑定失败时给出可操作的中文原因。
+func TestContractBindingErrorMessages(t *testing.T) {
+	want := map[error]string{
+		errBindingContractStatus:   "仅草稿合同可以绑定气瓶",
+		errBindingProductDisabled:  "所选气瓶已停用，不能绑定到合同",
+		errBindingProductScrapped:  "所选气瓶已报废，不能绑定到合同",
+		errBindingProductOwner:     "所选气瓶不属于该合同用户，请选择合同用户所属的气瓶",
+		errBindingProductDuplicate: "所选气瓶已绑定到该合同，请勿重复绑定",
+	}
+	for businessErr, message := range want {
+		if businessErr.Error() != message {
+			t.Fatalf("绑定错误提示不清晰：得到 %q，期望 %q", businessErr.Error(), message)
+		}
+	}
+}
+
 // TestContractActivationErrorMessages 验证关键启用失败原因保持清晰中文。
 func TestContractActivationErrorMessages(t *testing.T) {
 	want := map[error]string{

backend/api/internal/logic/platform/gasorder/gasorder.go

@@ -29,6 +29,11 @@ var (
 	errContractNotEffective    = errors.New("合同尚未到生效时间，暂时不能启用")
 	errContractExpired         = errors.New("合同已到期，请调整到期时间或续签后再启用")
 	errContractNoProduct       = errors.New("合同尚未绑定有效气瓶，请先绑定气瓶后再启用")
+	errBindingContractStatus   = errors.New("仅草稿合同可以绑定气瓶")
+	errBindingProductDisabled  = errors.New("所选气瓶已停用，不能绑定到合同")
+	errBindingProductScrapped  = errors.New("所选气瓶已报废，不能绑定到合同")
+	errBindingProductOwner     = errors.New("所选气瓶不属于该合同用户，请选择合同用户所属的气瓶")
+	errBindingProductDuplicate = errors.New("所选气瓶已绑定到该合同，请勿重复绑定")
 )
 
 func ListGasorderContract(ctx *gin.Context) { common.ListResource(ctx, &models.GasorderContract{}) }
@@ -424,14 +429,36 @@ func BindGasorderContractProduct(ctx *gin.Context) {
 		common.RespondRecordError(ctx, err)
 		return
 	}
-	if contract.ContractStatus != common.StatusDraft && contract.ContractStatus != common.StatusActive {
-		infra.Response.Error(ctx, errcode.ErrInvalidArgument)
+	if contract.ContractStatus != common.StatusDraft {
+		infra.Response.Error(ctx, errBindingContractStatus)
 		return
 	}
 	var product models.ProductInfo
-	if err := impl.DBService.Where("identity = ?", request.ProductIdentity).First(&product).Error; err != nil ||
-		product.Status != common.StatusEnable || product.ProductStatus == common.StatusScrapped || product.UserAccountID != contract.UserAccountID {
-		infra.Response.Error(ctx, errcode.ErrInvalidArgument)
+	if err := impl.DBService.Where("identity = ?", request.ProductIdentity).First(&product).Error; err != nil {
+		common.RespondRecordError(ctx, err)
+		return
+	}
+	if product.Status != common.StatusEnable {
+		infra.Response.Error(ctx, errBindingProductDisabled)
+		return
+	}
+	if product.ProductStatus == common.StatusScrapped {
+		infra.Response.Error(ctx, errBindingProductScrapped)
+		return
+	}
+	if product.UserAccountID != contract.UserAccountID {
+		infra.Response.Error(ctx, errBindingProductOwner)
+		return
+	}
+	var activeBindingCount int64
+	if err := impl.DBService.Model(&models.GasorderContractProduct{}).
+		Where("gasorder_contract_id = ? AND product_info_id = ? AND unbound_at IS NULL", contract.ID, product.ID).
+		Count(&activeBindingCount).Error; err != nil {
+		infra.Response.Error(ctx, err)
+		return
+	}
+	if activeBindingCount > 0 {
+		infra.Response.Error(ctx, errBindingProductDuplicate)
 		return
 	}
 	var productType models.ProductType

backend/api/internal/logic/platform/product/product.go

@@ -28,12 +28,31 @@ var productLifecycleStatuses = map[int]bool{
 
 func ProductInfoHandlers(relations ...common.ResourceRelation) (gin.HandlerFunc, gin.HandlerFunc, gin.HandlerFunc, gin.HandlerFunc) {
 	fields := []string{"code", "name", "params", "produced_at", "action", "reason", "remark"}
-	return func(ctx *gin.Context) { common.ListResource(ctx, &models.ProductInfo{}) },
+	return listProductInfo,
 		func(ctx *gin.Context) { createProductInfo(ctx, fields, relations) },
 		func(ctx *gin.Context) { common.GetResource(ctx, &models.ProductInfo{}) },
 		func(ctx *gin.Context) { updateProductInfo(ctx, fields, relations) }
 }
 
+// listProductInfo 按合同筛选可绑定气瓶；普通列表请求保持原有行为。
+func listProductInfo(ctx *gin.Context) {
+	contractIdentity := strings.TrimSpace(ctx.Query("contract_identity"))
+	if contractIdentity == "" {
+		common.ListResource(ctx, &models.ProductInfo{})
+		return
+	}
+	var contract models.GasorderContract
+	if err := impl.DBService.Where("identity = ?", contractIdentity).First(&contract).Error; err != nil {
+		common.RespondRecordError(ctx, err)
+		return
+	}
+	common.ListPageFiltered[models.ProductInfo](ctx, func(query *gorm.DB) *gorm.DB {
+		return query.
+			Where("status = ? AND product_status <> ? AND user_account_id = ?", common.StatusEnable, common.StatusScrapped, contract.UserAccountID).
+			Where("NOT EXISTS (SELECT 1 FROM gasorder_contract_product WHERE gasorder_contract_product.product_info_id = product_info.id AND gasorder_contract_product.gasorder_contract_id = ? AND gasorder_contract_product.unbound_at IS NULL)", contract.ID)
+	})
+}
+
 func createProductInfo(ctx *gin.Context, fields []string, relations []common.ResourceRelation) {
 	values, err := common.PrepareResourceValues(ctx, &models.ProductInfo{}, fields, relations)
 	if err != nil || !validParamsText(values["params"]) {