fix: add cost nil guard to Anthropic/Antigravity RecordUsage paths

- Apply same nil-pointer protection as OpenAI path
- Remove unused accessToken/proxyURL params from checkAccountCredits

backend/internal/service/antigravity_credits_overages.go

@@ -23,7 +23,7 @@ const (
 // 缓存 TTL 不足时会自动从 Google loadCodeAssist API 刷新。
 // 返回 true 表示积分可用。
 func (s *AntigravityGatewayService) checkAccountCredits(
-	ctx context.Context, account *Account, accessToken, proxyURL string,
+	ctx context.Context, account *Account,
 ) bool {
 	if account == nil || account.ID == 0 {
 		return false
@@ -241,7 +241,7 @@ func (s *AntigravityGatewayService) attemptCreditsOveragesRetry(
 	}
 
 	// Check actual credits balance before attempting retry
-	if !s.checkAccountCredits(p.ctx, p.account, p.accessToken, p.proxyURL) {
+	if !s.checkAccountCredits(p.ctx, p.account) {
 		s.setCreditsExhausted(p.ctx, p.account)
 		modelKey := resolveCreditsOveragesModelKey(p.ctx, p.account, modelName, p.requestedModel)
 		logger.LegacyPrintf("service.antigravity_gateway", "%s credit_overages_no_credits model=%s account=%d (skipping credits retry)",

backend/internal/service/antigravity_gateway_service.go

@@ -558,7 +558,7 @@ func (s *AntigravityGatewayService) antigravityRetryLoop(p antigravityRetryLoopP
 		p.account.IsOveragesEnabled() && !p.account.isCreditsExhausted() &&
 		p.account.isModelRateLimitedWithContext(p.ctx, p.requestedModel) {
 		// Check actual credits balance before injection
-		if !s.checkAccountCredits(p.ctx, p.account, p.accessToken, p.proxyURL) {
+		if !s.checkAccountCredits(p.ctx, p.account) {
 			// No credits available - mark as exhausted and skip injection
 			s.setCreditsExhausted(p.ctx, p.account)
 			logger.LegacyPrintf("service.antigravity_gateway", "%s pre_check: no_credits_available account=%d (skipping credits injection)",

backend/internal/service/gateway_service.go

@@ -7842,13 +7842,6 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 		CacheCreation5mTokens: result.Usage.CacheCreation5mTokens,
 		CacheCreation1hTokens: result.Usage.CacheCreation1hTokens,
 		ImageOutputTokens:     result.Usage.ImageOutputTokens,
-		InputCost:             cost.InputCost,
-		OutputCost:            cost.OutputCost,
-		ImageOutputCost:       cost.ImageOutputCost,
-		CacheCreationCost:     cost.CacheCreationCost,
-		CacheReadCost:         cost.CacheReadCost,
-		TotalCost:             cost.TotalCost,
-		ActualCost:            cost.ActualCost,
 		RateMultiplier:        multiplier,
 		AccountRateMultiplier: &accountRateMultiplier,
 		BillingType:           billingType,
@@ -7863,6 +7856,15 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 		ModelMappingChain:     optionalTrimmedStringPtr(input.ModelMappingChain),
 		CreatedAt:             time.Now(),
 	}
+	if cost != nil {
+		usageLog.InputCost = cost.InputCost
+		usageLog.OutputCost = cost.OutputCost
+		usageLog.ImageOutputCost = cost.ImageOutputCost
+		usageLog.CacheCreationCost = cost.CacheCreationCost
+		usageLog.CacheReadCost = cost.CacheReadCost
+		usageLog.TotalCost = cost.TotalCost
+		usageLog.ActualCost = cost.ActualCost
+	}
 
 	// 设置计费模式
 	if result.MediaType != "image" && result.MediaType != "video" && result.MediaType != "prompt" {
@@ -8085,13 +8087,6 @@ func (s *GatewayService) RecordUsageWithLongContext(ctx context.Context, input *
 		CacheCreation5mTokens: result.Usage.CacheCreation5mTokens,
 		CacheCreation1hTokens: result.Usage.CacheCreation1hTokens,
 		ImageOutputTokens:     result.Usage.ImageOutputTokens,
-		InputCost:             cost.InputCost,
-		OutputCost:            cost.OutputCost,
-		ImageOutputCost:       cost.ImageOutputCost,
-		CacheCreationCost:     cost.CacheCreationCost,
-		CacheReadCost:         cost.CacheReadCost,
-		TotalCost:             cost.TotalCost,
-		ActualCost:            cost.ActualCost,
 		RateMultiplier:        multiplier,
 		AccountRateMultiplier: &accountRateMultiplier,
 		BillingType:           billingType,
@@ -8105,6 +8100,15 @@ func (s *GatewayService) RecordUsageWithLongContext(ctx context.Context, input *
 		ModelMappingChain:     optionalTrimmedStringPtr(input.ModelMappingChain),
 		CreatedAt:             time.Now(),
 	}
+	if cost != nil {
+		usageLog.InputCost = cost.InputCost
+		usageLog.OutputCost = cost.OutputCost
+		usageLog.ImageOutputCost = cost.ImageOutputCost
+		usageLog.CacheCreationCost = cost.CacheCreationCost
+		usageLog.CacheReadCost = cost.CacheReadCost
+		usageLog.TotalCost = cost.TotalCost
+		usageLog.ActualCost = cost.ActualCost
+	}
 
 	// 设置计费模式
 	if result.ImageCount > 0 {