refactor(channels): tighten types and error paths per second review

- service: drop groupRepo nil guard (DI must inject), switch SupportedModels to SliceStable to match doc
- frontend: reuse user-side DTO types in SupportedModelChip/AvailableChannelsTable instead of duplicating shapes; narrow admin statusLabel param to ChannelStatus
- tests: replace nil-groupRepo case with ListAll/ListActive error propagation and BillingModelSource default-backfill coverage

backend/internal/service/channel.go

@@ -509,7 +509,7 @@ func (c *Channel) SupportedModels() []SupportedModel {
 		}
 	}
 
-	sort.Slice(result, func(i, j int) bool {
+	sort.SliceStable(result, func(i, j int) bool {
 		if result[i].Platform != result[j].Platform {
 			return result[i].Platform < result[j].Platform
 		}

backend/internal/service/channel_available.go

@@ -38,19 +38,17 @@ func (s *ChannelService) ListAvailable(ctx context.Context) ([]AvailableChannel,
 		return nil, fmt.Errorf("list channels: %w", err)
 	}
 
-	groupByID := make(map[int64]AvailableGroupRef)
-	if s.groupRepo != nil {
-		groups, err := s.groupRepo.ListActive(ctx)
-		if err != nil {
-			return nil, fmt.Errorf("list active groups: %w", err)
-		}
-		for i := range groups {
-			g := groups[i]
-			groupByID[g.ID] = AvailableGroupRef{
-				ID:       g.ID,
-				Name:     g.Name,
-				Platform: g.Platform,
-			}
+	groups, err := s.groupRepo.ListActive(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("list active groups: %w", err)
+	}
+	groupByID := make(map[int64]AvailableGroupRef, len(groups))
+	for i := range groups {
+		g := groups[i]
+		groupByID[g.ID] = AvailableGroupRef{
+			ID:       g.ID,
+			Name:     g.Name,
+			Platform: g.Platform,
 		}
 	}
 

backend/internal/service/channel_available_test.go

@@ -4,6 +4,7 @@ package service
 
 import (
 	"context"
+	"errors"
 	"testing"
 
 	"github.com/Wei-Shaw/sub2api/internal/pkg/pagination"
@@ -12,11 +13,16 @@ import (
 
 // stubGroupRepoForAvailable 是 ListAvailable 测试用的 GroupRepository stub，
 // 仅实现 ListActive；其他方法对本测试无关，返回零值即可。
+// listActiveErr 非 nil 时，ListActive 返回该错误用于错误传播测试。
 type stubGroupRepoForAvailable struct {
-	activeGroups []Group
+	activeGroups  []Group
+	listActiveErr error
 }
 
 func (s *stubGroupRepoForAvailable) ListActive(ctx context.Context) ([]Group, error) {
+	if s.listActiveErr != nil {
+		return nil, s.listActiveErr
+	}
 	return s.activeGroups, nil
 }
 
@@ -61,7 +67,7 @@ func (s *stubGroupRepoForAvailable) UpdateSortOrders(ctx context.Context, update
 }
 
 // newAvailableChannelService 构造一个 ChannelService，channelRepo.ListAll 返回给定 channels，
-// groupRepo 由参数决定（可传 nil 测试 nil 分支）。
+// groupRepo 由参数决定。传入空 stub 表示「活跃分组列表为空」。
 func newAvailableChannelService(channels []Channel, groupRepo GroupRepository) *ChannelService {
 	repo := &mockChannelRepository{
 		listAllFn: func(ctx context.Context) ([]Channel, error) { return channels, nil },
@@ -69,15 +75,15 @@ func newAvailableChannelService(channels []Channel, groupRepo GroupRepository) *
 	return NewChannelService(repo, groupRepo, nil)
 }
 
-func TestListAvailable_NilGroupRepo_NoGroupsAttached(t *testing.T) {
-	// groupRepo 为 nil 时不应 panic，且每个渠道的 Groups 应为空切片。
+func TestListAvailable_EmptyActiveGroups_NoGroupsAttached(t *testing.T) {
+	// 活跃分组列表为空时，渠道的 Groups 应为空切片，不报错。
 	channels := []Channel{{
 		ID:       1,
 		Name:     "chA",
 		Status:   StatusActive,
 		GroupIDs: []int64{10, 20},
 	}}
-	svc := newAvailableChannelService(channels, nil)
+	svc := newAvailableChannelService(channels, &stubGroupRepoForAvailable{})
 	out, err := svc.ListAvailable(context.Background())
 	require.NoError(t, err)
 	require.Len(t, out, 1)
@@ -109,7 +115,7 @@ func TestListAvailable_SortedByName(t *testing.T) {
 		{ID: 2, Name: "Alpha"},
 		{ID: 3, Name: "charlie"},
 	}
-	svc := newAvailableChannelService(channels, nil)
+	svc := newAvailableChannelService(channels, &stubGroupRepoForAvailable{})
 	out, err := svc.ListAvailable(context.Background())
 	require.NoError(t, err)
 	require.Len(t, out, 3)
@@ -117,3 +123,42 @@ func TestListAvailable_SortedByName(t *testing.T) {
 	require.Equal(t, "beta", out[1].Name)
 	require.Equal(t, "charlie", out[2].Name)
 }
+
+func TestListAvailable_ListAllErrorPropagates(t *testing.T) {
+	// ListAll 返回错误时 ListAvailable 应直接返回包装后的错误，不再访问 groupRepo。
+	sentinel := errors.New("list-all-boom")
+	repo := &mockChannelRepository{
+		listAllFn: func(ctx context.Context) ([]Channel, error) { return nil, sentinel },
+	}
+	svc := NewChannelService(repo, &stubGroupRepoForAvailable{}, nil)
+	out, err := svc.ListAvailable(context.Background())
+	require.Nil(t, out)
+	require.ErrorIs(t, err, sentinel)
+}
+
+func TestListAvailable_ListActiveErrorPropagates(t *testing.T) {
+	// groupRepo.ListActive 返回错误时 ListAvailable 应直接返回包装后的错误。
+	sentinel := errors.New("list-active-boom")
+	svc := newAvailableChannelService(
+		[]Channel{{ID: 1, Name: "chA"}},
+		&stubGroupRepoForAvailable{listActiveErr: sentinel},
+	)
+	out, err := svc.ListAvailable(context.Background())
+	require.Nil(t, out)
+	require.ErrorIs(t, err, sentinel)
+}
+
+func TestListAvailable_DefaultsEmptyBillingModelSource(t *testing.T) {
+	// 渠道 BillingModelSource 为空时应回填为 BillingModelSourceChannelMapped，
+	// 显式值应原样保留（由 service 层统一处理，避免各 handler 重复默认逻辑）。
+	channels := []Channel{
+		{ID: 1, Name: "empty", BillingModelSource: ""},
+		{ID: 2, Name: "explicit", BillingModelSource: BillingModelSourceUpstream},
+	}
+	svc := newAvailableChannelService(channels, &stubGroupRepoForAvailable{})
+	out, err := svc.ListAvailable(context.Background())
+	require.NoError(t, err)
+	require.Len(t, out, 2)
+	require.Equal(t, BillingModelSourceChannelMapped, out[0].BillingModelSource)
+	require.Equal(t, BillingModelSourceUpstream, out[1].BillingModelSource)
+}