fix: improve sticky session scheduling

backend/internal/repository/scheduler_cache.go

@@ -449,11 +449,69 @@ func buildSchedulerMetadataAccount(account service.Account) service.Account {
 		SessionWindowStart:      account.SessionWindowStart,
 		SessionWindowEnd:        account.SessionWindowEnd,
 		SessionWindowStatus:     account.SessionWindowStatus,
+		AccountGroups:           filterSchedulerAccountGroups(account.AccountGroups),
+		GroupIDs:                filterSchedulerGroupIDs(account.GroupIDs, account.AccountGroups),
 		Credentials:             filterSchedulerCredentials(account.Credentials),
 		Extra:                   filterSchedulerExtra(account.Extra),
 	}
 }
 
+func filterSchedulerAccountGroups(accountGroups []service.AccountGroup) []service.AccountGroup {
+	if len(accountGroups) == 0 {
+		return nil
+	}
+
+	filtered := make([]service.AccountGroup, 0, len(accountGroups))
+	for _, ag := range accountGroups {
+		if ag.GroupID <= 0 {
+			continue
+		}
+		filtered = append(filtered, service.AccountGroup{
+			AccountID: ag.AccountID,
+			GroupID:   ag.GroupID,
+			Priority:  ag.Priority,
+			CreatedAt: ag.CreatedAt,
+		})
+	}
+	if len(filtered) == 0 {
+		return nil
+	}
+	return filtered
+}
+
+func filterSchedulerGroupIDs(groupIDs []int64, accountGroups []service.AccountGroup) []int64 {
+	if len(groupIDs) == 0 && len(accountGroups) == 0 {
+		return nil
+	}
+
+	seen := make(map[int64]struct{}, len(groupIDs)+len(accountGroups))
+	filtered := make([]int64, 0, len(groupIDs)+len(accountGroups))
+	for _, id := range groupIDs {
+		if id <= 0 {
+			continue
+		}
+		if _, ok := seen[id]; ok {
+			continue
+		}
+		seen[id] = struct{}{}
+		filtered = append(filtered, id)
+	}
+	for _, ag := range accountGroups {
+		if ag.GroupID <= 0 {
+			continue
+		}
+		if _, ok := seen[ag.GroupID]; ok {
+			continue
+		}
+		seen[ag.GroupID] = struct{}{}
+		filtered = append(filtered, ag.GroupID)
+	}
+	if len(filtered) == 0 {
+		return nil
+	}
+	return filtered
+}
+
 func filterSchedulerCredentials(credentials map[string]any) map[string]any {
 	if len(credentials) == 0 {
 		return nil

backend/internal/repository/scheduler_cache_integration_test.go

@@ -56,6 +56,15 @@ func TestSchedulerCacheSnapshotUsesSlimMetadataButKeepsFullAccount(t *testing.T)
 		SessionWindowStart:     &now,
 		SessionWindowEnd:       &windowEnd,
 		SessionWindowStatus:    "active",
+		GroupIDs:               []int64{bucket.GroupID},
+		AccountGroups: []service.AccountGroup{
+			{
+				AccountID: 101,
+				GroupID:   bucket.GroupID,
+				Priority:  5,
+				Group:     &service.Group{ID: bucket.GroupID, Name: "gemini-group"},
+			},
+		},
 	}
 
 	require.NoError(t, cache.SetSnapshot(ctx, bucket, []service.Account{account}))
@@ -79,10 +88,17 @@ func TestSchedulerCacheSnapshotUsesSlimMetadataButKeepsFullAccount(t *testing.T)
 	require.Equal(t, 4, got.GetMaxSessions())
 	require.Equal(t, 11, got.GetSessionIdleTimeoutMinutes())
 	require.Nil(t, got.Extra["unused_large_field"])
+	require.Equal(t, []int64{bucket.GroupID}, got.GroupIDs)
+	require.Len(t, got.AccountGroups, 1)
+	require.Equal(t, account.ID, got.AccountGroups[0].AccountID)
+	require.Equal(t, bucket.GroupID, got.AccountGroups[0].GroupID)
+	require.Nil(t, got.AccountGroups[0].Group)
 
 	full, err := cache.GetAccount(ctx, account.ID)
 	require.NoError(t, err)
 	require.NotNil(t, full)
 	require.Equal(t, "secret-access-token", full.GetCredential("access_token"))
 	require.Equal(t, strings.Repeat("x", 4096), full.GetCredential("huge_blob"))
+	require.Len(t, full.AccountGroups, 1)
+	require.NotNil(t, full.AccountGroups[0].Group)
 }

backend/internal/repository/scheduler_cache_unit_test.go

@@ -31,3 +31,43 @@ func TestBuildSchedulerMetadataAccount_KeepsOpenAIWSFlags(t *testing.T) {
 	require.Equal(t, true, got.Extra["mixed_scheduling"])
 	require.Nil(t, got.Extra["unused_large_field"])
 }
+
+func TestBuildSchedulerMetadataAccount_KeepsSlimGroupMembership(t *testing.T) {
+	account := service.Account{
+		ID:       42,
+		Platform: service.PlatformAnthropic,
+		GroupIDs: []int64{7, 9, 7, 0},
+		AccountGroups: []service.AccountGroup{
+			{
+				AccountID: 42,
+				GroupID:   7,
+				Priority:  2,
+				Account:   &service.Account{ID: 42, Name: "drop-from-metadata"},
+				Group:     &service.Group{ID: 7, Name: "drop-from-metadata"},
+			},
+			{
+				AccountID: 42,
+				GroupID:   11,
+				Priority:  3,
+				Group:     &service.Group{ID: 11, Name: "drop-from-metadata"},
+			},
+			{
+				AccountID: 42,
+				GroupID:   0,
+				Priority:  4,
+			},
+		},
+	}
+
+	got := buildSchedulerMetadataAccount(account)
+
+	require.Equal(t, []int64{7, 9, 11}, got.GroupIDs)
+	require.Len(t, got.AccountGroups, 2)
+	require.Equal(t, int64(42), got.AccountGroups[0].AccountID)
+	require.Equal(t, int64(7), got.AccountGroups[0].GroupID)
+	require.Equal(t, 2, got.AccountGroups[0].Priority)
+	require.Nil(t, got.AccountGroups[0].Account)
+	require.Nil(t, got.AccountGroups[0].Group)
+	require.Equal(t, int64(11), got.AccountGroups[1].GroupID)
+	require.Nil(t, got.Groups)
+}