优化 Responses 生图意图复用

backend/internal/handler/openai_gateway_handler.go

@@ -124,6 +124,13 @@ func openAICompatibleRequestPlatform(apiKey *service.APIKey) string {
 	return service.PlatformOpenAI
 }
 
+func openAIResponsesRequiredCapability(imageIntent bool, platform string) service.OpenAIEndpointCapability {
+	if imageIntent && platform == service.PlatformOpenAI {
+		return service.OpenAIEndpointCapabilityResponses
+	}
+	return service.OpenAIEndpointCapabilityChatCompletions
+}
+
 func allowOpenAICompatibleMessagesDispatch(apiKey *service.APIKey) bool {
 	if apiKey == nil || apiKey.Group == nil {
 		return true
@@ -363,12 +370,9 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 	// 生图意图的 /v1/responses 请求必须调度到确实支持 Responses API 的账号，否则
 	// 会在 forward 阶段被静默降级为无法生图的 Chat Completions 直转（#4417）。
 	// 仅对 OpenAI 平台生效：Grok 生图走独立的 forwardGrokResponses 路径，不应被过滤。
-	// 使用 IsExplicitImageGenerationIntent 排除被动 image_gen namespace 声明，
-	// 避免 Codex 的被动工具目录使 CC-only 账号被误过滤（#4476）。
-	requiredCapability := service.OpenAIEndpointCapabilityChatCompletions
-	if service.IsExplicitImageGenerationIntent("/v1/responses", reqModel, body) && requestPlatform == service.PlatformOpenAI {
-		requiredCapability = service.OpenAIEndpointCapabilityResponses
-	}
+	// 复用前置权限与并发阶段在未修改 body 上确认的显式生图意图，避免大 tools 请求重复扫描。
+	// 该判断已排除 Codex 被动 image_gen namespace，避免 CC-only 账号被误过滤（#4476）。
+	requiredCapability := openAIResponsesRequiredCapability(imageIntent, requestPlatform)
 
 	for {
 		// Streaming Forward intentionally detaches the upstream request so usage can

backend/internal/handler/openai_gateway_handler_test.go

@@ -138,6 +138,39 @@ func TestOpenAIForwardSucceededForScheduling(t *testing.T) {
 	}))
 }
 
+func TestOpenAIResponsesRequiredCapability(t *testing.T) {
+	tests := []struct {
+		name        string
+		imageIntent bool
+		platform    string
+		want        service.OpenAIEndpointCapability
+	}{
+		{
+			name:        "OpenAI explicit image intent requires Responses",
+			imageIntent: true,
+			platform:    service.PlatformOpenAI,
+			want:        service.OpenAIEndpointCapabilityResponses,
+		},
+		{
+			name:        "Grok explicit image intent keeps chat capability",
+			imageIntent: true,
+			platform:    service.PlatformGrok,
+			want:        service.OpenAIEndpointCapabilityChatCompletions,
+		},
+		{
+			name:     "non-image intent keeps chat capability",
+			platform: service.PlatformOpenAI,
+			want:     service.OpenAIEndpointCapabilityChatCompletions,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.want, openAIResponsesRequiredCapability(tt.imageIntent, tt.platform))
+		})
+	}
+}
+
 func TestResolveOpenAIMessagesMetadataSession_DoesNotDerivePromptCacheKey(t *testing.T) {
 	body := []byte(`{"model":"claude-sonnet-4-5","metadata":{"user_id":"claude-code-session"},"messages":[{"role":"user","content":"hello"}]}`)
 

backend/internal/handler/openai_responses_image_intent_benchmark_test.go

@@ -0,0 +1,53 @@
+package handler
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/service"
+)
+
+var openAIResponsesImageIntentRoutingBenchmarkSink service.OpenAIEndpointCapability
+
+func BenchmarkOpenAIResponsesImageIntentRouting_LargeToolsBody(b *testing.B) {
+	body := buildLargeOpenAIResponsesToolsBody(32 << 20)
+	if service.IsExplicitImageGenerationIntent("/v1/responses", "gpt-5.4", body) {
+		b.Fatal("large tools body must not have explicit image intent")
+	}
+	platform := service.PlatformOpenAI
+
+	b.Run("reuse_once", func(b *testing.B) {
+		b.SetBytes(int64(len(body)))
+		b.ReportAllocs()
+		for range b.N {
+			imageIntent := service.IsExplicitImageGenerationIntent("/v1/responses", "gpt-5.4", body)
+			openAIResponsesImageIntentRoutingBenchmarkSink = openAIResponsesRequiredCapability(imageIntent, platform)
+		}
+	})
+
+	b.Run("rescan_twice", func(b *testing.B) {
+		b.SetBytes(int64(len(body)))
+		b.ReportAllocs()
+		for range b.N {
+			imageIntent := service.IsExplicitImageGenerationIntent("/v1/responses", "gpt-5.4", body)
+			// 对照优化前路径：路由阶段会再次扫描同一份未修改的 body。
+			requiredCapability := service.OpenAIEndpointCapabilityChatCompletions
+			if service.IsExplicitImageGenerationIntent("/v1/responses", "gpt-5.4", body) && platform == service.PlatformOpenAI {
+				requiredCapability = service.OpenAIEndpointCapabilityResponses
+			}
+			if imageIntent && requiredCapability != service.OpenAIEndpointCapabilityResponses {
+				b.Fatal("explicit image intent must require Responses")
+			}
+			openAIResponsesImageIntentRoutingBenchmarkSink = requiredCapability
+		}
+	})
+}
+
+func buildLargeOpenAIResponsesToolsBody(targetBytes int) []byte {
+	var builder strings.Builder
+	builder.Grow(targetBytes + 256)
+	_, _ = builder.WriteString(`{"model":"gpt-5.4","tools":[{"type":"function","name":"search","description":"`)
+	_, _ = builder.WriteString(strings.Repeat("x", targetBytes))
+	_, _ = builder.WriteString(`"}],"tool_choice":"auto","input":"write code"}`)
+	return []byte(builder.String())
+}