fix(usage): preserve requested model in gateway billing paths

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/internal/service/gateway_record_usage_test.go

@@ -162,6 +162,32 @@ func TestGatewayServiceRecordUsage_BillingFingerprintFallsBackToContextRequestID
 	require.Equal(t, "local:req-local-123", billingRepo.lastCmd.RequestPayloadHash)
 }
 
+func TestGatewayServiceRecordUsage_PreservesRequestedAndUpstreamModels(t *testing.T) {
+	usageRepo := &openAIRecordUsageLogRepoStub{inserted: true}
+	svc := newGatewayRecordUsageServiceForTest(usageRepo, &openAIRecordUsageUserRepoStub{}, &openAIRecordUsageSubRepoStub{})
+	mappedModel := "claude-sonnet-4-20250514"
+
+	err := svc.RecordUsage(context.Background(), &RecordUsageInput{
+		Result: &ForwardResult{
+			RequestID:     "gateway_models_split",
+			Usage:         ClaudeUsage{InputTokens: 10, OutputTokens: 6},
+			Model:         "claude-sonnet-4",
+			UpstreamModel: mappedModel,
+			Duration:      time.Second,
+		},
+		APIKey:  &APIKey{ID: 501, Quota: 100},
+		User:    &User{ID: 601},
+		Account: &Account{ID: 701},
+	})
+
+	require.NoError(t, err)
+	require.NotNil(t, usageRepo.lastLog)
+	require.Equal(t, "claude-sonnet-4", usageRepo.lastLog.Model)
+	require.Equal(t, "claude-sonnet-4", usageRepo.lastLog.RequestedModel)
+	require.NotNil(t, usageRepo.lastLog.UpstreamModel)
+	require.Equal(t, mappedModel, *usageRepo.lastLog.UpstreamModel)
+}
+
 func TestGatewayServiceRecordUsage_UsageLogWriteErrorDoesNotSkipBilling(t *testing.T) {
 	usageRepo := &openAIRecordUsageLogRepoStub{inserted: false, err: MarkUsageLogCreateNotPersisted(context.Canceled)}
 	userRepo := &openAIRecordUsageUserRepoStub{}

backend/internal/service/gateway_service.go

@@ -482,10 +482,12 @@ type ClaudeUsage struct {
 
 // ForwardResult 转发结果
 type ForwardResult struct {
-	RequestID        string
-	Usage            ClaudeUsage
-	Model            string
-	UpstreamModel    string // Actual upstream model after mapping (empty = no mapping)
+	RequestID string
+	Usage     ClaudeUsage
+	Model     string
+	// UpstreamModel is the actual upstream model after mapping.
+	// Prefer empty when it is identical to Model; persistence normalizes equal values away as no-op mappings.
+	UpstreamModel    string
 	Stream           bool
 	Duration         time.Duration
 	FirstTokenMs     *int // 首字时间（流式请求）
@@ -7516,6 +7518,7 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 	}
 
 	var cost *CostBreakdown
+	billingModel := forwardResultBillingModel(result.Model, result.UpstreamModel)
 
 	// 根据请求类型选择计费方式
 	if result.MediaType == "image" || result.MediaType == "video" {
@@ -7531,7 +7534,7 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 		if result.MediaType == "image" {
 			cost = s.billingService.CalculateSoraImageCost(result.ImageSize, result.ImageCount, soraConfig, multiplier)
 		} else {
-			cost = s.billingService.CalculateSoraVideoCost(result.Model, soraConfig, multiplier)
+			cost = s.billingService.CalculateSoraVideoCost(billingModel, soraConfig, multiplier)
 		}
 	} else if result.MediaType == "prompt" {
 		cost = &CostBreakdown{}
@@ -7545,7 +7548,7 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 				Price4K: apiKey.Group.ImagePrice4K,
 			}
 		}
-		cost = s.billingService.CalculateImageCost(result.Model, result.ImageSize, result.ImageCount, groupConfig, multiplier)
+		cost = s.billingService.CalculateImageCost(billingModel, result.ImageSize, result.ImageCount, groupConfig, multiplier)
 	} else {
 		// Token 计费
 		tokens := UsageTokens{
@@ -7557,7 +7560,7 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 			CacheCreation1hTokens: result.Usage.CacheCreation1hTokens,
 		}
 		var err error
-		cost, err = s.billingService.CalculateCost(result.Model, tokens, multiplier)
+		cost, err = s.billingService.CalculateCost(billingModel, tokens, multiplier)
 		if err != nil {
 			logger.LegacyPrintf("service.gateway", "Calculate cost failed: %v", err)
 			cost = &CostBreakdown{ActualCost: 0}
@@ -7589,6 +7592,7 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 		AccountID:             account.ID,
 		RequestID:             requestID,
 		Model:                 result.Model,
+		RequestedModel:        result.Model,
 		UpstreamModel:         optionalNonEqualStringPtr(result.UpstreamModel, result.Model),
 		ReasoningEffort:       result.ReasoningEffort,
 		InboundEndpoint:       optionalTrimmedStringPtr(input.InboundEndpoint),
@@ -7719,6 +7723,7 @@ func (s *GatewayService) RecordUsageWithLongContext(ctx context.Context, input *
 	}
 
 	var cost *CostBreakdown
+	billingModel := forwardResultBillingModel(result.Model, result.UpstreamModel)
 
 	// 根据请求类型选择计费方式
 	if result.ImageCount > 0 {
@@ -7731,7 +7736,7 @@ func (s *GatewayService) RecordUsageWithLongContext(ctx context.Context, input *
 				Price4K: apiKey.Group.ImagePrice4K,
 			}
 		}
-		cost = s.billingService.CalculateImageCost(result.Model, result.ImageSize, result.ImageCount, groupConfig, multiplier)
+		cost = s.billingService.CalculateImageCost(billingModel, result.ImageSize, result.ImageCount, groupConfig, multiplier)
 	} else {
 		// Token 计费（使用长上下文计费方法）
 		tokens := UsageTokens{
@@ -7743,7 +7748,7 @@ func (s *GatewayService) RecordUsageWithLongContext(ctx context.Context, input *
 			CacheCreation1hTokens: result.Usage.CacheCreation1hTokens,
 		}
 		var err error
-		cost, err = s.billingService.CalculateCostWithLongContext(result.Model, tokens, multiplier, input.LongContextThreshold, input.LongContextMultiplier)
+		cost, err = s.billingService.CalculateCostWithLongContext(billingModel, tokens, multiplier, input.LongContextThreshold, input.LongContextMultiplier)
 		if err != nil {
 			logger.LegacyPrintf("service.gateway", "Calculate cost failed: %v", err)
 			cost = &CostBreakdown{ActualCost: 0}
@@ -7771,6 +7776,7 @@ func (s *GatewayService) RecordUsageWithLongContext(ctx context.Context, input *
 		AccountID:             account.ID,
 		RequestID:             requestID,
 		Model:                 result.Model,
+		RequestedModel:        result.Model,
 		UpstreamModel:         optionalNonEqualStringPtr(result.UpstreamModel, result.Model),
 		ReasoningEffort:       result.ReasoningEffort,
 		InboundEndpoint:       optionalTrimmedStringPtr(input.InboundEndpoint),

backend/internal/service/openai_gateway_record_usage_test.go

@@ -879,6 +879,7 @@ func TestOpenAIGatewayServiceRecordUsage_UsesRequestedModelAndUpstreamModelMetad
 	require.NoError(t, err)
 	require.NotNil(t, usageRepo.lastLog)
 	require.Equal(t, "gpt-5.1", usageRepo.lastLog.Model)
+	require.Equal(t, "gpt-5.1", usageRepo.lastLog.RequestedModel)
 	require.NotNil(t, usageRepo.lastLog.UpstreamModel)
 	require.Equal(t, "gpt-5.1-codex", *usageRepo.lastLog.UpstreamModel)
 	require.NotNil(t, usageRepo.lastLog.ServiceTier)
@@ -894,6 +895,40 @@ func TestOpenAIGatewayServiceRecordUsage_UsesRequestedModelAndUpstreamModelMetad
 	require.Equal(t, 1, userRepo.deductCalls)
 }
 
+func TestOpenAIGatewayServiceRecordUsage_BillsMappedRequestsUsingUpstreamModelFallback(t *testing.T) {
+	usageRepo := &openAIRecordUsageLogRepoStub{inserted: true}
+	userRepo := &openAIRecordUsageUserRepoStub{}
+	subRepo := &openAIRecordUsageSubRepoStub{}
+	svc := newOpenAIRecordUsageServiceForTest(usageRepo, userRepo, subRepo, nil)
+	usage := OpenAIUsage{InputTokens: 20, OutputTokens: 10}
+
+	expectedCost, err := svc.billingService.CalculateCost("gpt-5.1-codex", UsageTokens{
+		InputTokens:  20,
+		OutputTokens: 10,
+	}, 1.1)
+	require.NoError(t, err)
+
+	err = svc.RecordUsage(context.Background(), &OpenAIRecordUsageInput{
+		Result: &OpenAIForwardResult{
+			RequestID:     "resp_upstream_model_billing_fallback",
+			Model:         "gpt-5.1",
+			UpstreamModel: "gpt-5.1-codex",
+			Usage:         usage,
+			Duration:      time.Second,
+		},
+		APIKey:  &APIKey{ID: 10},
+		User:    &User{ID: 20},
+		Account: &Account{ID: 30},
+	})
+
+	require.NoError(t, err)
+	require.NotNil(t, usageRepo.lastLog)
+	require.Equal(t, "gpt-5.1", usageRepo.lastLog.Model)
+	require.Equal(t, expectedCost.ActualCost, usageRepo.lastLog.ActualCost)
+	require.Equal(t, expectedCost.TotalCost, usageRepo.lastLog.TotalCost)
+	require.Equal(t, expectedCost.ActualCost, userRepo.lastAmount)
+}
+
 func TestOpenAIGatewayServiceRecordUsage_SubscriptionBillingSetsSubscriptionFields(t *testing.T) {
 	usageRepo := &openAIRecordUsageLogRepoStub{inserted: true}
 	userRepo := &openAIRecordUsageUserRepoStub{}

backend/internal/service/openai_gateway_service.go

@@ -4110,9 +4110,9 @@ func (s *OpenAIGatewayService) RecordUsage(ctx context.Context, input *OpenAIRec
 		multiplier = resolver.Resolve(ctx, user.ID, *apiKey.GroupID, apiKey.Group.RateMultiplier)
 	}
 
-	billingModel := result.Model
+	billingModel := forwardResultBillingModel(result.Model, result.UpstreamModel)
 	if result.BillingModel != "" {
-		billingModel = result.BillingModel
+		billingModel = strings.TrimSpace(result.BillingModel)
 	}
 	serviceTier := ""
 	if result.ServiceTier != nil {
@@ -4140,6 +4140,7 @@ func (s *OpenAIGatewayService) RecordUsage(ctx context.Context, input *OpenAIRec
 		AccountID:             account.ID,
 		RequestID:             requestID,
 		Model:                 result.Model,
+		RequestedModel:        result.Model,
 		UpstreamModel:         optionalNonEqualStringPtr(result.UpstreamModel, result.Model),
 		ServiceTier:           result.ServiceTier,
 		ReasoningEffort:       result.ReasoningEffort,