From 3c5ea297ffe82521e0209aea9cfb1cf397434cc6 Mon Sep 17 00:00:00 2001
From: Yujun Kim <hi@yujun.kim>
Date: Sat, 26 Sep 2026 20:11:03 +0900
Subject: [PATCH] fix(billing): keep zero-cost usage log when Free Fast has no
 pricing

RecordUsage treats a missing price as zero cost on the first pass, but
the Free Fast Standard re-evaluation returned the same pricing error.
Requests in a free_openai_fast group sent at priority/fast tier to a
model without pricing therefore lost their usage log entirely.

Ignore pricing-unavailable errors on the Standard pass and keep the
zero-cost entry, matching the first pass.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 .../openai_gateway_record_usage_test.go       | 45 +++++++++++++++++++
 .../internal/service/openai_gateway_usage.go  |  6 ++-
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/backend/internal/service/openai_gateway_record_usage_test.go b/backend/internal/service/openai_gateway_record_usage_test.go
index b7682cb400..be4cf1850c 100644
--- a/backend/internal/service/openai_gateway_record_usage_test.go
+++ b/backend/internal/service/openai_gateway_record_usage_test.go
@@ -3210,6 +3210,51 @@ func TestOpenAIGatewayServiceRecordUsage_FreeOpenAIFastChargesStandard(t *testin
 	require.InDelta(t, standardTotal*0.5, usageRepo.lastLog.ActualCost, 1e-10)
 }
 
+func TestOpenAIGatewayServiceRecordUsage_FreeOpenAIFastMissingPricingRecordsZeroCostUsageLog(t *testing.T) {
+	usageRepo := &openAIRecordUsageLogRepoStub{inserted: true}
+	svc := newOpenAIRecordUsageServiceForTest(
+		usageRepo,
+		&openAIRecordUsageUserRepoStub{},
+		&openAIRecordUsageSubRepoStub{},
+		nil,
+	)
+	svc.resolver = NewModelPricingResolver(nil, svc.billingService)
+	groupID := int64(78)
+	serviceTier := "priority"
+	apiKey := &APIKey{
+		ID:      1021,
+		GroupID: &groupID,
+		Group: &Group{
+			ID: groupID, Platform: PlatformOpenAI, Status: StatusActive,
+			Hydrated: true, RateMultiplier: 1, FreeOpenAIFast: true,
+		},
+	}
+
+	err := svc.RecordUsage(context.Background(), &OpenAIRecordUsageInput{
+		Result: &OpenAIForwardResult{
+			RequestID:   "resp_free_fast_missing_pricing",
+			ServiceTier: &serviceTier,
+			Usage:       OpenAIUsage{InputTokens: 1200, OutputTokens: 300},
+			Model:       "pricing-missing-test-model",
+			Duration:    time.Second,
+		},
+		APIKey:  apiKey,
+		User:    &User{ID: 2021},
+		Account: &Account{ID: 3021, Platform: PlatformOpenAI, Type: AccountTypeAPIKey},
+	})
+
+	require.NoError(t, err)
+	require.Equal(t, 1, usageRepo.calls)
+	require.NotNil(t, usageRepo.lastLog)
+	require.Equal(t, "resp_free_fast_missing_pricing", usageRepo.lastLog.RequestID)
+	require.Equal(t, 1200, usageRepo.lastLog.InputTokens)
+	require.Equal(t, 300, usageRepo.lastLog.OutputTokens)
+	require.NotNil(t, usageRepo.lastLog.ServiceTier)
+	require.Equal(t, "priority", *usageRepo.lastLog.ServiceTier)
+	require.Zero(t, usageRepo.lastLog.TotalCost)
+	require.Zero(t, usageRepo.lastLog.ActualCost)
+}
+
 func TestGroupBillsOpenAIFastAtStandardRequiresOpenAIAccount(t *testing.T) {
 	apiKey := &APIKey{Group: &Group{Platform: PlatformComposite, FreeOpenAIFast: true}}
 
diff --git a/backend/internal/service/openai_gateway_usage.go b/backend/internal/service/openai_gateway_usage.go
index cd2c7aadea..f42d81b488 100644
--- a/backend/internal/service/openai_gateway_usage.go
+++ b/backend/internal/service/openai_gateway_usage.go
@@ -314,10 +314,12 @@ func (s *OpenAIGatewayService) RecordUsage(ctx context.Context, input *OpenAIRec
 			longContextBillingGate,
 			pricingAt,
 		)
-		if standardErr != nil {
+		if standardErr != nil && !isUsagePricingUnavailableError(standardErr) {
 			return standardErr
 		}
-		if cost != nil && standardCost != nil {
+		// Missing pricing already fell back to a zero-cost log above; keep that
+		// usage row instead of dropping it on the Standard re-evaluation.
+		if standardErr == nil && cost != nil && standardCost != nil {
 			cost.ActualCost = standardCost.ActualCost
 		}
 	}