diff --git a/backend/internal/repository/usage_log_repo_request_type_test.go b/backend/internal/repository/usage_log_repo_request_type_test.go
index 670ef6e7..597c9597 100644
--- a/backend/internal/repository/usage_log_repo_request_type_test.go
+++ b/backend/internal/repository/usage_log_repo_request_type_test.go
@@ -263,7 +263,9 @@ func TestPrepareUsageLogInsert_PersistsImageSizeMetadata(t *testing.T) {
 	require.Equal(t, sql.NullString{String: inputSize, Valid: true}, prepared.args[35])
 	require.Equal(t, sql.NullString{String: outputSize, Valid: true}, prepared.args[36])
 	require.Equal(t, sql.NullString{String: source, Valid: true}, prepared.args[37])
-	require.JSONEq(t, `{"1K":1,"4K":1}`, prepared.args[38].(string))
+	breakdownJSON, ok := prepared.args[38].(string)
+	require.True(t, ok)
+	require.JSONEq(t, `{"1K":1,"4K":1}`, breakdownJSON)
 }
 
 func TestCoalesceTrimmedString(t *testing.T) {
diff --git a/backend/internal/service/antigravity_gateway_service.go b/backend/internal/service/antigravity_gateway_service.go
index 9491b8f6..cfae171d 100644
--- a/backend/internal/service/antigravity_gateway_service.go
+++ b/backend/internal/service/antigravity_gateway_service.go
@@ -4065,11 +4065,6 @@ func (s *AntigravityGatewayService) handleClaudeStreamingResponse(c *gin.Context
 	}
 }
 
-// extractImageSize 从 Gemini 请求中提取 image_size 参数
-func (s *AntigravityGatewayService) extractImageSize(body []byte) string {
-	return normalizeOpenAIImageSizeTier(s.extractImageInputSize(body))
-}
-
 func (s *AntigravityGatewayService) extractImageInputSize(body []byte) string {
 	var req antigravity.GeminiRequest
 	if err := json.Unmarshal(body, &req); err != nil {
diff --git a/backend/internal/service/gemini_messages_compat_service.go b/backend/internal/service/gemini_messages_compat_service.go
index 4342f87d..ea9903a7 100644
--- a/backend/internal/service/gemini_messages_compat_service.go
+++ b/backend/internal/service/gemini_messages_compat_service.go
@@ -3434,11 +3434,6 @@ func convertClaudeGenerationConfig(req map[string]any) map[string]any {
 	return out
 }
 
-// extractImageSize 从 Gemini 请求中提取 image_size 参数
-func (s *GeminiMessagesCompatService) extractImageSize(body []byte) string {
-	return normalizeOpenAIImageSizeTier(s.extractImageInputSize(body))
-}
-
 func (s *GeminiMessagesCompatService) extractImageInputSize(body []byte) string {
 	var req struct {
 		GenerationConfig *struct {
diff --git a/backend/internal/service/image_generation_intent.go b/backend/internal/service/image_generation_intent.go
index f51b7ee7..4aca1239 100644
--- a/backend/internal/service/image_generation_intent.go
+++ b/backend/internal/service/image_generation_intent.go
@@ -176,14 +176,6 @@ type OpenAIResponsesImageBillingConfig struct {
 	InputSize string
 }
 
-func resolveOpenAIResponsesImageBillingConfig(reqBody map[string]any, fallbackModel string) (string, string, error) {
-	cfg, err := resolveOpenAIResponsesImageBillingConfigDetailed(reqBody, fallbackModel)
-	if err != nil {
-		return "", "", err
-	}
-	return cfg.Model, cfg.SizeTier, nil
-}
-
 func resolveOpenAIResponsesImageBillingConfigDetailed(reqBody map[string]any, fallbackModel string) (OpenAIResponsesImageBillingConfig, error) {
 	imageModel := ""
 	imageSize := ""