fix(billing): resolve shadow credential tier contract

backend/internal/service/openai_gateway_record_usage_test.go

@@ -3001,6 +3001,50 @@ func TestOpenAIGatewayServiceRecordUsage_CodexDefaultEchoKeepsFastBilling(t *tes
 	}
 }
 
+func TestOpenAIGatewayServiceRecordUsage_ShadowUsesParentCredentialTierContract(t *testing.T) {
+	usageRepo := &openAIRecordUsageLogRepoStub{inserted: true}
+	svc := newOpenAIRecordUsageServiceForTest(
+		usageRepo,
+		&openAIRecordUsageUserRepoStub{},
+		&openAIRecordUsageSubRepoStub{},
+		nil,
+	)
+	parentID := int64(9001)
+	accountRepo := &openAIRecordUsageAccountRepoStub{account: &Account{
+		ID: parentID, Platform: PlatformOpenAI, Type: AccountTypeOAuth,
+	}}
+	svc.accountRepo = accountRepo
+	serviceTier := "priority"
+	tokens := UsageTokens{InputTokens: 100, OutputTokens: 50}
+
+	err := svc.RecordUsage(context.Background(), &OpenAIRecordUsageInput{
+		Result: &OpenAIForwardResult{
+			RequestID:                   "resp_shadow_codex_default_echo",
+			ServiceTier:                 &serviceTier,
+			UpstreamResponseServiceTier: "default",
+			Usage:                       OpenAIUsage{InputTokens: tokens.InputTokens, OutputTokens: tokens.OutputTokens},
+			Model:                       "gpt-5.6-sol",
+			Duration:                    time.Second,
+		},
+		APIKey: &APIKey{ID: 1020},
+		User:   &User{ID: 2020},
+		Account: &Account{
+			ID: 3020, Platform: PlatformOpenAI, Type: AccountTypeAPIKey,
+			ParentAccountID: &parentID,
+		},
+	})
+
+	require.NoError(t, err)
+	require.Equal(t, 1, accountRepo.calls)
+	require.NotNil(t, usageRepo.lastLog)
+	require.NotNil(t, usageRepo.lastLog.ServiceTier)
+	require.Equal(t, "priority", *usageRepo.lastLog.ServiceTier)
+
+	fastCost, calcErr := svc.billingService.CalculateCostWithServiceTier("gpt-5.6-sol", tokens, 1.0, "priority")
+	require.NoError(t, calcErr)
+	require.InDelta(t, fastCost.TotalCost, usageRepo.lastLog.TotalCost, 1e-10)
+}
+
 func TestOpenAIGatewayServiceRecordUsage_ServiceTierNeverRaisedByUpstreamResponse(t *testing.T) {
 	usageRepo := &openAIRecordUsageLogRepoStub{inserted: true}
 	userRepo := &openAIRecordUsageUserRepoStub{}

backend/internal/service/openai_gateway_usage.go

@@ -143,10 +143,14 @@ func (s *OpenAIGatewayService) RecordUsage(ctx context.Context, input *OpenAIRec
 	user := input.User
 	account := input.Account
 	subscription := input.Subscription
+	billingAccount, err := resolveCredentialAccount(ctx, s.accountRepo, account)
+	if err != nil {
+		return err
+	}
 	if !isGrokVideoUsageResult(result, nil) {
 		ApplyOpenAIImageBillingResolution(result)
 	}
-	logServiceTierBillingDowngrade("service.openai_gateway", account, result.RequestID, ApplyOpenAIServiceTierBillingResolution(account, result))
+	logServiceTierBillingDowngrade("service.openai_gateway", account, result.RequestID, ApplyOpenAIServiceTierBillingResolution(billingAccount, result))
 
 	// OpenAI input_tokens 是总输入，包含缓存读取和缓存写入明细。
 	// 将三类 token 拆成互斥桶，避免缓存写入同时按普通输入和 cache_write 重复计费。
@@ -183,7 +187,6 @@ func (s *OpenAIGatewayService) RecordUsage(ctx context.Context, input *OpenAIRec
 	videoMultiplier := resolveVideoRateMultiplier(apiKey, baseMultiplier)
 
 	var cost *CostBreakdown
-	var err error
 	billingModel := forwardResultBillingModel(result.Model, result.UpstreamModel)
 	if result.BillingModel != "" {
 		billingModel = strings.TrimSpace(result.BillingModel)
@@ -207,13 +210,6 @@ func (s *OpenAIGatewayService) RecordUsage(ctx context.Context, input *OpenAIRec
 	if result.ServiceTier != nil {
 		serviceTier = strings.TrimSpace(*result.ServiceTier)
 	}
-	billingAccount := account
-	if account.IsShadow() {
-		billingAccount, err = resolveCredentialAccount(ctx, s.accountRepo, account)
-		if err != nil {
-			return err
-		}
-	}
 	longContextBillingGate := openAILongContextBillingGate(billingAccount)
 	cost, err = s.calculateOpenAIRecordUsageCost(
 		ctx,