refactor(channels): normalize at cache fill and eliminate frontend as-cast

- channel.go: convert normalizeBillingModelSource into a (*Channel) method for entity cohesion
- channel_service.go: normalize in populateChannelCache so every cache-backed reader (gateway, billing, future endpoints) sees the default; drop the duplicate fallback inside resolveMapping
- table: tighten Row with status?: ChannelStatus / billing_model_source?: BillingModelSource, remove the [key: string]: unknown index signature
- admin view: drop the `as ChannelStatus` / `as BillingModelSource` assertions and add statusStyleOf / billingSourceLabelOf helpers with runtime fallback so unseen values render as "-" instead of crashing

backend/internal/service/channel.go

@@ -111,6 +111,18 @@ func (c *Channel) IsActive() bool {
 	return c.Status == StatusActive
 }
 
+// normalizeBillingModelSource 若 BillingModelSource 为空则回填默认值 ChannelMapped。
+// 作为 *Channel 的实体方法集中管理默认值，service 层只需在 Channel 进入内存
+// （缓存装填、repo 读出）时调用一次，下游读路径就无需重复兜底。
+func (c *Channel) normalizeBillingModelSource() {
+	if c == nil {
+		return
+	}
+	if c.BillingModelSource == "" {
+		c.BillingModelSource = BillingModelSourceChannelMapped
+	}
+}
+
 // GetModelPricing 根据模型名查找渠道定价，未找到返回 nil。
 // 精确匹配，大小写不敏感。返回值拷贝，不污染缓存。
 func (c *Channel) GetModelPricing(model string) *ChannelModelPricing {

backend/internal/service/channel_available.go

@@ -66,7 +66,7 @@ func (s *ChannelService) ListAvailable(ctx context.Context) ([]AvailableChannel,
 		}
 		sort.SliceStable(groups, func(i, j int) bool { return groups[i].Name < groups[j].Name })
 
-		normalizeBillingModelSource(ch)
+		ch.normalizeBillingModelSource()
 
 		out = append(out, AvailableChannel{
 			ID:                 ch.ID,

backend/internal/service/channel_service.go

@@ -301,6 +301,9 @@ func (s *ChannelService) fetchChannelData(ctx context.Context) ([]Channel, map[i
 }
 
 // populateChannelCache 将渠道列表和分组平台映射填充到缓存快照中。
+// 装填时对每个 Channel 统一归一化 BillingModelSource，让缓存命中的所有下游
+// （gateway routing / billing / 未来任何 cache-backed 读路径）都拿到已归一化的实体，
+// 避免"每个出口各自记得 normalize"反模式。
 func populateChannelCache(channels []Channel, groupPlatforms map[int64]string) *channelCache {
 	cache := newEmptyChannelCache()
 	cache.groupPlatform = groupPlatforms
@@ -308,6 +311,7 @@ func populateChannelCache(channels []Channel, groupPlatforms map[int64]string) *
 	cache.loadedAt = time.Now()
 
 	for i := range channels {
+		channels[i].normalizeBillingModelSource()
 		ch := &channels[i]
 		cache.byID[ch.ID] = ch
 		for _, gid := range ch.GroupIDs {
@@ -518,14 +522,13 @@ func (s *ChannelService) ResolveChannelMappingAndRestrict(ctx context.Context, g
 // resolveMapping 基于已查找的渠道信息解析模型映射。
 // antigravity 分组依次尝试所有匹配平台，确保跨平台同名映射各自独立。
 func resolveMapping(lk *channelLookup, groupID int64, model string) ChannelMappingResult {
+	// lk.channel 来自已装填的缓存，BillingModelSource 已在 populateChannelCache 阶段归一化，
+	// 这里无需重复兜底。
 	result := ChannelMappingResult{
 		MappedModel:        model,
 		ChannelID:          lk.channel.ID,
 		BillingModelSource: lk.channel.BillingModelSource,
 	}
-	if result.BillingModelSource == "" {
-		result.BillingModelSource = BillingModelSourceChannelMapped
-	}
 
 	modelLower := strings.ToLower(model)
 	if mapped := lookupMappingAcrossPlatforms(lk.cache, groupID, lk.platform, modelLower); mapped != "" {
@@ -686,7 +689,7 @@ func (s *ChannelService) Create(ctx context.Context, input *CreateChannelInput)
 		ApplyPricingToAccountStats: input.ApplyPricingToAccountStats,
 		AccountStatsPricingRules:   input.AccountStatsPricingRules,
 	}
-	normalizeBillingModelSource(channel)
+	channel.normalizeBillingModelSource()
 
 	if err := validateChannelConfig(channel.ModelPricing, channel.ModelMapping); err != nil {
 		return nil, err
@@ -706,7 +709,7 @@ func (s *ChannelService) Create(ctx context.Context, input *CreateChannelInput)
 	if err != nil {
 		return nil, err
 	}
-	normalizeBillingModelSource(created)
+	created.normalizeBillingModelSource()
 	return created, nil
 }
 
@@ -717,18 +720,10 @@ func (s *ChannelService) GetByID(ctx context.Context, id int64) (*Channel, error
 	if err != nil {
 		return nil, err
 	}
-	normalizeBillingModelSource(ch)
+	ch.normalizeBillingModelSource()
 	return ch, nil
 }
 
-// normalizeBillingModelSource 若 BillingModelSource 为空则回填默认值 ChannelMapped。
-// 统一在 service 层完成，避免 handler 响应层重复兜底。
-func normalizeBillingModelSource(ch *Channel) {
-	if ch != nil && ch.BillingModelSource == "" {
-		ch.BillingModelSource = BillingModelSourceChannelMapped
-	}
-}
-
 // Update 更新渠道
 func (s *ChannelService) Update(ctx context.Context, id int64, input *UpdateChannelInput) (*Channel, error) {
 	channel, err := s.repo.GetByID(ctx, id)
@@ -762,7 +757,7 @@ func (s *ChannelService) Update(ctx context.Context, id int64, input *UpdateChan
 	if err != nil {
 		return nil, err
 	}
-	normalizeBillingModelSource(updated)
+	updated.normalizeBillingModelSource()
 	return updated, nil
 }
 
@@ -886,7 +881,7 @@ func (s *ChannelService) List(ctx context.Context, params pagination.PaginationP
 		return nil, nil, err
 	}
 	for i := range channels {
-		normalizeBillingModelSource(&channels[i])
+		channels[i].normalizeBillingModelSource()
 	}
 	return channels, res, nil
 }

frontend/src/components/channels/AvailableChannelsTable.vue

@@ -62,6 +62,7 @@ import DataTable from '@/components/common/DataTable.vue'
 import Icon from '@/components/icons/Icon.vue'
 import SupportedModelChip from './SupportedModelChip.vue'
 import type { UserSupportedModel } from '@/api/channels'
+import type { ChannelStatus, BillingModelSource } from '@/constants/channel'
 
 interface GroupRef {
   id: number
@@ -75,7 +76,10 @@ interface Row {
   groups: GroupRef[]
   // 复用 user 侧最小 DTO；admin 侧 SupportedModel 结构上是其超集，可直接传入。
   supported_models: UserSupportedModel[]
-  [key: string]: unknown
+  // admin 独有字段：用精确类型代替 `unknown`，让消费端无需 `as` 断言，
+  // 也能在后端新增 union 成员时让前端 Record 查表立刻出空而非崩溃。
+  status?: ChannelStatus
+  billing_model_source?: BillingModelSource
 }
 
 interface Column {

frontend/src/views/admin/AvailableChannelsView.vue

@@ -46,16 +46,16 @@
 
           <template #cell-status="{ row }">
             <span
-              :class="statusStyles[row.status as ChannelStatus].cls"
+              :class="statusStyleOf(row.status).cls"
               class="inline-flex items-center rounded px-2 py-0.5 text-xs font-medium"
             >
-              {{ statusStyles[row.status as ChannelStatus].label }}
+              {{ statusStyleOf(row.status).label }}
             </span>
           </template>
 
           <template #cell-billing_model_source="{ row }">
             <span class="text-xs text-gray-700 dark:text-gray-300">
-              {{ billingSourceLabels[row.billing_model_source as BillingModelSource] }}
+              {{ billingSourceLabelOf(row.billing_model_source) }}
             </span>
           </template>
         </AvailableChannelsTable>
@@ -101,7 +101,7 @@ const columns = computed(() => [
 
 /**
  * 显示样式：i18n label + Tailwind class，按 ChannelStatus 完整穷举。
- * 用 Record<ChannelStatus, ...> 强制未来新增状态时 TS 编译失败，避免遗漏分支。
+ * Record 键类型强制未来新增 ChannelStatus 成员时 TS 编译失败，避免遗漏分支。
  */
 const statusStyles = computed<Record<ChannelStatus, { label: string; cls: string }>>(() => ({
   [CHANNEL_STATUS_ACTIVE]: {
@@ -124,6 +124,19 @@ const billingSourceLabels = computed<Record<BillingModelSource, string>>(() => (
   [BILLING_MODEL_SOURCE_CHANNEL_MAPPED]: t('admin.availableChannels.billingSource.channel_mapped')
 }))
 
+// 运行时兜底：即便 service 层归一化漏点或后端新增未同步的 enum 值传入，
+// 也不会触发 undefined.cls 崩溃；统一降级为 "-"。
+const DEFAULT_STATUS_STYLE = { label: '-', cls: '' }
+const DEFAULT_BILLING_LABEL = '-'
+
+function statusStyleOf(status: ChannelStatus | undefined): { label: string; cls: string } {
+  return status ? statusStyles.value[status] : DEFAULT_STATUS_STYLE
+}
+
+function billingSourceLabelOf(src: BillingModelSource | undefined): string {
+  return src ? billingSourceLabels.value[src] : DEFAULT_BILLING_LABEL
+}
+
 const filteredChannels = computed(() => {
   const q = searchQuery.value.trim().toLowerCase()
   if (!q) return channels.value