优化透传图片意图判定复用

backend/internal/service/openai_gateway_passthrough.go

@@ -100,7 +100,8 @@ func (s *OpenAIGatewayService) forwardOpenAIPassthrough(
 	body = updatedBody
 
 	apiKey := getAPIKeyFromContext(c)
-	if IsImageGenerationIntent(openAIResponsesEndpoint, reqModel, body) && !GroupAllowsImageGeneration(apiKeyGroup(apiKey)) {
+	imageIntent := IsImageGenerationIntent(openAIResponsesEndpoint, reqModel, body)
+	if imageIntent && !GroupAllowsImageGeneration(apiKeyGroup(apiKey)) {
 		MarkOpsClientBusinessLimited(c, OpsClientBusinessLimitedReasonLocalFeatureGate)
 		c.JSON(http.StatusForbidden, gin.H{
 			"error": gin.H{
@@ -113,7 +114,7 @@ func (s *OpenAIGatewayService) forwardOpenAIPassthrough(
 	imageBillingModel := ""
 	imageSizeTier := ""
 	imageInputSize := ""
-	if IsImageGenerationIntent(openAIResponsesEndpoint, reqModel, body) {
+	if imageIntent {
 		var imageCfgErr error
 		imageCfg, imageCfgErr := resolveOpenAIResponsesImageBillingConfigDetailedFromBody(body, reqModel)
 		if imageCfgErr != nil {

backend/internal/service/openai_gateway_passthrough_image_intent_benchmark_test.go

@@ -0,0 +1,27 @@
+package service
+
+import "testing"
+
+var passthroughImageIntentBenchmarkSink bool
+
+func BenchmarkOpenAIPassthroughImageIntentReuse_LargeBody(b *testing.B) {
+	body := buildLargeOpenAIResponsesImageToolBody(32 << 20)
+
+	b.Run("Once", func(b *testing.B) {
+		b.SetBytes(int64(len(body)))
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			passthroughImageIntentBenchmarkSink = IsImageGenerationIntent(openAIResponsesEndpoint, "gpt-5.4", body)
+		}
+	})
+
+	b.Run("Twice", func(b *testing.B) {
+		b.SetBytes(int64(len(body)))
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			permissionIntent := IsImageGenerationIntent(openAIResponsesEndpoint, "gpt-5.4", body)
+			billingIntent := IsImageGenerationIntent(openAIResponsesEndpoint, "gpt-5.4", body)
+			passthroughImageIntentBenchmarkSink = permissionIntent && billingIntent
+		}
+	})
+}

backend/internal/service/openai_gateway_passthrough_image_intent_test.go

@@ -0,0 +1,59 @@
+package service
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestOpenAIGatewayService_APIKeyPassthrough_ImageIntentPreservesGateAndBilling(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	body := []byte(`{"model":"gpt-5.4","stream":false,"tools":[{"type":"image_generation","model":"gpt-image-2","size":"2048x1152"}],"input":"draw"}`)
+
+	t.Run("disabled group rejects before upstream", func(t *testing.T) {
+		upstream := &httpUpstreamRecorder{}
+		svc := newOpenAIImageGenerationControlTestService(upstream)
+		c, recorder := newOpenAIImageGenerationControlTestContext(false, "curl/8.0")
+		account := newOpenAIImageGenerationControlTestAccount()
+		account.Extra = map[string]any{"openai_passthrough": true}
+
+		result, err := svc.Forward(context.Background(), c, account, body)
+
+		require.Error(t, err)
+		require.Nil(t, result)
+		require.Equal(t, http.StatusForbidden, recorder.Code)
+		require.Equal(t, "permission_error", gjson.GetBytes(recorder.Body.Bytes(), "error.type").String())
+		require.Nil(t, upstream.lastReq)
+	})
+
+	t.Run("allowed group keeps image billing", func(t *testing.T) {
+		upstream := &httpUpstreamRecorder{resp: &http.Response{
+			StatusCode: http.StatusOK,
+			Header:     http.Header{"Content-Type": []string{"application/json"}},
+			Body: io.NopCloser(strings.NewReader(
+				`{"output":[{"id":"ig_1","type":"image_generation_call","result":"final-image","size":"2048x1152"}],"usage":{"input_tokens":1,"output_tokens":2}}`,
+			)),
+		}}
+		svc := newOpenAIImageGenerationControlTestService(upstream)
+		c, _ := newOpenAIImageGenerationControlTestContext(true, "curl/8.0")
+		account := newOpenAIImageGenerationControlTestAccount()
+		account.Extra = map[string]any{"openai_passthrough": true}
+
+		result, err := svc.Forward(context.Background(), c, account, body)
+
+		require.NoError(t, err)
+		require.NotNil(t, result)
+		require.NotNil(t, upstream.lastReq)
+		require.Equal(t, body, upstream.lastBody)
+		require.Equal(t, 1, result.ImageCount)
+		require.Equal(t, "gpt-image-2", result.BillingModel)
+		require.Equal(t, "2K", result.ImageSize)
+		require.Equal(t, "2048x1152", result.ImageInputSize)
+	})
+}