feat(openai-ws): 合并 WS v2 透传模式与前端 ws mode

新增 OpenAI WebSocket v2 passthrough relay 数据面与服务适配层，支持按账号 ws mode 在 ctx_pool 与 passthrough 间路由。同步调整前端 OpenAI ws mode 选项为 off/ctx_pool/passthrough，并补充 i18n 文案与对应单测。新增 Caddyfile.dmit 与 docker-compose-aicodex.yml 部署配置，用于宿主机场景下的反向代理与服务编排。 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-03-05 11:50:58 +08:00
parent 078fefed03
commit 1d0872e7ca
27 changed files with 3322 additions and 81 deletions
--- a/backend/internal/config/config.go
+++ b/backend/internal/config/config.go
@@ -516,7 +516,7 @@ func (c *UserMessageQueueConfig) GetEffectiveMode() string {
 type GatewayOpenAIWSConfig struct {
 	// ModeRouterV2Enabled: 新版 WS mode 路由开关（默认 false；关闭时保持 legacy 行为）
 	ModeRouterV2Enabled bool `mapstructure:"mode_router_v2_enabled"`
-	// IngressModeDefault: ingress 默认模式（off/shared/dedicated）
+	// IngressModeDefault: ingress 默认模式（off/ctx_pool/passthrough）
 	IngressModeDefault string `mapstructure:"ingress_mode_default"`
 	// Enabled: 全局总开关（默认 true）
 	Enabled bool `mapstructure:"enabled"`
@@ -1335,7 +1335,7 @@ func setDefaults() {
 	// OpenAI Responses WebSocket（默认开启；可通过 force_http 紧急回滚）
 	viper.SetDefault("gateway.openai_ws.enabled", true)
 	viper.SetDefault("gateway.openai_ws.mode_router_v2_enabled", false)
-	viper.SetDefault("gateway.openai_ws.ingress_mode_default", "shared")
+	viper.SetDefault("gateway.openai_ws.ingress_mode_default", "ctx_pool")
 	viper.SetDefault("gateway.openai_ws.oauth_enabled", true)
 	viper.SetDefault("gateway.openai_ws.apikey_enabled", true)
 	viper.SetDefault("gateway.openai_ws.force_http", false)
@@ -2043,9 +2043,11 @@ func (c *Config) Validate() error {
 	}
 	if mode := strings.ToLower(strings.TrimSpace(c.Gateway.OpenAIWS.IngressModeDefault)); mode != "" {
 		switch mode {
-		case "off", "shared", "dedicated":
+		case "off", "ctx_pool", "passthrough":
+		case "shared", "dedicated":
+			slog.Warn("gateway.openai_ws.ingress_mode_default is deprecated, treating as ctx_pool; please update to off|ctx_pool|passthrough", "value", mode)
 		default:
-			return fmt.Errorf("gateway.openai_ws.ingress_mode_default must be one of off|shared|dedicated")
+			return fmt.Errorf("gateway.openai_ws.ingress_mode_default must be one of off|ctx_pool|passthrough")
 		}
 	}
 	if mode := strings.ToLower(strings.TrimSpace(c.Gateway.OpenAIWS.StoreDisabledConnMode)); mode != "" {
--- a/backend/internal/config/config_test.go
+++ b/backend/internal/config/config_test.go
@@ -153,8 +153,8 @@ func TestLoadDefaultOpenAIWSConfig(t *testing.T) {
 	if cfg.Gateway.OpenAIWS.ModeRouterV2Enabled {
 		t.Fatalf("Gateway.OpenAIWS.ModeRouterV2Enabled = true, want false")
 	}
-	if cfg.Gateway.OpenAIWS.IngressModeDefault != "shared" {
-		t.Fatalf("Gateway.OpenAIWS.IngressModeDefault = %q, want %q", cfg.Gateway.OpenAIWS.IngressModeDefault, "shared")
+	if cfg.Gateway.OpenAIWS.IngressModeDefault != "ctx_pool" {
+		t.Fatalf("Gateway.OpenAIWS.IngressModeDefault = %q, want %q", cfg.Gateway.OpenAIWS.IngressModeDefault, "ctx_pool")
 	}
 }

@@ -1373,7 +1373,7 @@ func TestValidateConfig_OpenAIWSRules(t *testing.T) {
 			wantErr: "gateway.openai_ws.store_disabled_conn_mode",
 		},
 		{
-			name:    "ingress_mode_default 必须为 off|shared|dedicated",
+			name:    "ingress_mode_default 必须为 off|ctx_pool|passthrough",
 			mutate:  func(c *Config) { c.Gateway.OpenAIWS.IngressModeDefault = "invalid" },
 			wantErr: "gateway.openai_ws.ingress_mode_default",
 		},
--- a/backend/internal/service/account.go
+++ b/backend/internal/service/account.go
@@ -853,15 +853,21 @@ func (a *Account) IsOpenAIResponsesWebSocketV2Enabled() bool {
 }

 const (
-	OpenAIWSIngressModeOff       = "off"
-	OpenAIWSIngressModeShared    = "shared"
-	OpenAIWSIngressModeDedicated = "dedicated"
+	OpenAIWSIngressModeOff         = "off"
+	OpenAIWSIngressModeShared      = "shared"
+	OpenAIWSIngressModeDedicated   = "dedicated"
+	OpenAIWSIngressModeCtxPool     = "ctx_pool"
+	OpenAIWSIngressModePassthrough = "passthrough"
 )

 func normalizeOpenAIWSIngressMode(mode string) string {
 	switch strings.ToLower(strings.TrimSpace(mode)) {
 	case OpenAIWSIngressModeOff:
 		return OpenAIWSIngressModeOff
+	case OpenAIWSIngressModeCtxPool:
+		return OpenAIWSIngressModeCtxPool
+	case OpenAIWSIngressModePassthrough:
+		return OpenAIWSIngressModePassthrough
 	case OpenAIWSIngressModeShared:
 		return OpenAIWSIngressModeShared
 	case OpenAIWSIngressModeDedicated:
@@ -873,18 +879,21 @@ func normalizeOpenAIWSIngressMode(mode string) string {

 func normalizeOpenAIWSIngressDefaultMode(mode string) string {
 	if normalized := normalizeOpenAIWSIngressMode(mode); normalized != "" {
+		if normalized == OpenAIWSIngressModeShared || normalized == OpenAIWSIngressModeDedicated {
+			return OpenAIWSIngressModeCtxPool
+		}
 		return normalized
 	}
-	return OpenAIWSIngressModeShared
+	return OpenAIWSIngressModeCtxPool
 }

-// ResolveOpenAIResponsesWebSocketV2Mode 返回账号在 WSv2 ingress 下的有效模式（off/shared/dedicated）。
+// ResolveOpenAIResponsesWebSocketV2Mode 返回账号在 WSv2 ingress 下的有效模式（off/ctx_pool/passthrough）。
 //
 // 优先级：
 // 1. 分类型 mode 新字段（string）
 // 2. 分类型 enabled 旧字段（bool）
 // 3. 兼容 enabled 旧字段（bool）
-// 4. defaultMode（非法时回退 shared）
+// 4. defaultMode（非法时回退 ctx_pool）
 func (a *Account) ResolveOpenAIResponsesWebSocketV2Mode(defaultMode string) string {
 	resolvedDefault := normalizeOpenAIWSIngressDefaultMode(defaultMode)
 	if a == nil || !a.IsOpenAI() {
@@ -919,7 +928,7 @@ func (a *Account) ResolveOpenAIResponsesWebSocketV2Mode(defaultMode string) stri
 			return "", false
 		}
 		if enabled {
-			return OpenAIWSIngressModeShared, true
+			return OpenAIWSIngressModeCtxPool, true
 		}
 		return OpenAIWSIngressModeOff, true
 	}
@@ -946,6 +955,10 @@ func (a *Account) ResolveOpenAIResponsesWebSocketV2Mode(defaultMode string) stri
 	if mode, ok := resolveBoolMode("openai_ws_enabled"); ok {
 		return mode
 	}
+	// 兼容旧值：shared/dedicated 语义都归并到 ctx_pool。
+	if resolvedDefault == OpenAIWSIngressModeShared || resolvedDefault == OpenAIWSIngressModeDedicated {
+		return OpenAIWSIngressModeCtxPool
+	}
 	return resolvedDefault
 }

--- a/backend/internal/service/account_openai_passthrough_test.go
+++ b/backend/internal/service/account_openai_passthrough_test.go
@@ -206,14 +206,14 @@ func TestAccount_IsOpenAIResponsesWebSocketV2Enabled(t *testing.T) {
 }

 func TestAccount_ResolveOpenAIResponsesWebSocketV2Mode(t *testing.T) {
-	t.Run("default fallback to shared", func(t *testing.T) {
+	t.Run("default fallback to ctx_pool", func(t *testing.T) {
 		account := &Account{
 			Platform: PlatformOpenAI,
 			Type:     AccountTypeOAuth,
 			Extra:    map[string]any{},
 		}
-		require.Equal(t, OpenAIWSIngressModeShared, account.ResolveOpenAIResponsesWebSocketV2Mode(""))
-		require.Equal(t, OpenAIWSIngressModeShared, account.ResolveOpenAIResponsesWebSocketV2Mode("invalid"))
+		require.Equal(t, OpenAIWSIngressModeCtxPool, account.ResolveOpenAIResponsesWebSocketV2Mode(""))
+		require.Equal(t, OpenAIWSIngressModeCtxPool, account.ResolveOpenAIResponsesWebSocketV2Mode("invalid"))
 	})

 	t.Run("oauth mode field has highest priority", func(t *testing.T) {
@@ -221,15 +221,15 @@ func TestAccount_ResolveOpenAIResponsesWebSocketV2Mode(t *testing.T) {
 			Platform: PlatformOpenAI,
 			Type:     AccountTypeOAuth,
 			Extra: map[string]any{
-				"openai_oauth_responses_websockets_v2_mode":    OpenAIWSIngressModeDedicated,
+				"openai_oauth_responses_websockets_v2_mode":    OpenAIWSIngressModePassthrough,
 				"openai_oauth_responses_websockets_v2_enabled": false,
 				"responses_websockets_v2_enabled":              false,
 			},
 		}
-		require.Equal(t, OpenAIWSIngressModeDedicated, account.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeShared))
+		require.Equal(t, OpenAIWSIngressModePassthrough, account.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeCtxPool))
 	})

-	t.Run("legacy enabled maps to shared", func(t *testing.T) {
+	t.Run("legacy enabled maps to ctx_pool", func(t *testing.T) {
 		account := &Account{
 			Platform: PlatformOpenAI,
 			Type:     AccountTypeAPIKey,
@@ -237,7 +237,28 @@ func TestAccount_ResolveOpenAIResponsesWebSocketV2Mode(t *testing.T) {
 				"responses_websockets_v2_enabled": true,
 			},
 		}
-		require.Equal(t, OpenAIWSIngressModeShared, account.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeOff))
+		require.Equal(t, OpenAIWSIngressModeCtxPool, account.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeOff))
+	})
+
+	t.Run("shared/dedicated mode strings are compatible with ctx_pool", func(t *testing.T) {
+		shared := &Account{
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Extra: map[string]any{
+				"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeShared,
+			},
+		}
+		dedicated := &Account{
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Extra: map[string]any{
+				"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeDedicated,
+			},
+		}
+		require.Equal(t, OpenAIWSIngressModeShared, shared.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeOff))
+		require.Equal(t, OpenAIWSIngressModeDedicated, dedicated.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeOff))
+		require.Equal(t, OpenAIWSIngressModeCtxPool, normalizeOpenAIWSIngressDefaultMode(OpenAIWSIngressModeShared))
+		require.Equal(t, OpenAIWSIngressModeCtxPool, normalizeOpenAIWSIngressDefaultMode(OpenAIWSIngressModeDedicated))
 	})

 	t.Run("legacy disabled maps to off", func(t *testing.T) {
@@ -249,7 +270,7 @@ func TestAccount_ResolveOpenAIResponsesWebSocketV2Mode(t *testing.T) {
 				"responses_websockets_v2_enabled":               true,
 			},
 		}
-		require.Equal(t, OpenAIWSIngressModeOff, account.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeShared))
+		require.Equal(t, OpenAIWSIngressModeOff, account.ResolveOpenAIResponsesWebSocketV2Mode(OpenAIWSIngressModeCtxPool))
 	})

 	t.Run("non openai always off", func(t *testing.T) {
--- a/backend/internal/service/openai_gateway_service.go
+++ b/backend/internal/service/openai_gateway_service.go
@@ -263,13 +263,15 @@ type OpenAIGatewayService struct {
 	toolCorrector       *CodexToolCorrector
 	openaiWSResolver    OpenAIWSProtocolResolver

-	openaiWSPoolOnce       sync.Once
-	openaiWSStateStoreOnce sync.Once
-	openaiSchedulerOnce    sync.Once
-	openaiWSPool           *openAIWSConnPool
-	openaiWSStateStore     OpenAIWSStateStore
-	openaiScheduler        OpenAIAccountScheduler
-	openaiAccountStats     *openAIAccountRuntimeStats
+	openaiWSPoolOnce              sync.Once
+	openaiWSStateStoreOnce        sync.Once
+	openaiSchedulerOnce           sync.Once
+	openaiWSPassthroughDialerOnce sync.Once
+	openaiWSPool                  *openAIWSConnPool
+	openaiWSStateStore            OpenAIWSStateStore
+	openaiScheduler               OpenAIAccountScheduler
+	openaiWSPassthroughDialer     openAIWSClientDialer
+	openaiAccountStats            *openAIAccountRuntimeStats

 	openaiWSFallbackUntil sync.Map // key: int64(accountID), value: time.Time
 	openaiWSRetryMetrics  openAIWSRetryMetrics
--- a/backend/internal/service/openai_ws_client.go
+++ b/backend/internal/service/openai_ws_client.go
@@ -11,6 +11,7 @@ import (
 	"sync/atomic"
 	"time"

+	openaiwsv2 "github.com/Wei-Shaw/sub2api/internal/service/openai_ws_v2"
 	coderws "github.com/coder/websocket"
 	"github.com/coder/websocket/wsjson"
 )
@@ -234,6 +235,8 @@ type coderOpenAIWSClientConn struct {
 	conn *coderws.Conn
 }

+var _ openaiwsv2.FrameConn = (*coderOpenAIWSClientConn)(nil)
+
 func (c *coderOpenAIWSClientConn) WriteJSON(ctx context.Context, value any) error {
 	if c == nil || c.conn == nil {
 		return errOpenAIWSConnClosed
@@ -264,6 +267,30 @@ func (c *coderOpenAIWSClientConn) ReadMessage(ctx context.Context) ([]byte, erro
 	}
 }

+func (c *coderOpenAIWSClientConn) ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error) {
+	if c == nil || c.conn == nil {
+		return coderws.MessageText, nil, errOpenAIWSConnClosed
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	msgType, payload, err := c.conn.Read(ctx)
+	if err != nil {
+		return coderws.MessageText, nil, err
+	}
+	return msgType, payload, nil
+}
+
+func (c *coderOpenAIWSClientConn) WriteFrame(ctx context.Context, msgType coderws.MessageType, payload []byte) error {
+	if c == nil || c.conn == nil {
+		return errOpenAIWSConnClosed
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	return c.conn.Write(ctx, msgType, payload)
+}
+
 func (c *coderOpenAIWSClientConn) Ping(ctx context.Context) error {
 	if c == nil || c.conn == nil {
 		return errOpenAIWSConnClosed
--- a/backend/internal/service/openai_ws_forwarder.go
+++ b/backend/internal/service/openai_ws_forwarder.go
@@ -46,9 +46,10 @@ const (
 	openAIWSPayloadSizeEstimateMaxBytes = 64 * 1024
 	openAIWSPayloadSizeEstimateMaxItems = 16

-	openAIWSEventFlushBatchSizeDefault = 4
-	openAIWSEventFlushIntervalDefault  = 25 * time.Millisecond
-	openAIWSPayloadLogSampleDefault    = 0.2
+	openAIWSEventFlushBatchSizeDefault    = 4
+	openAIWSEventFlushIntervalDefault     = 25 * time.Millisecond
+	openAIWSPayloadLogSampleDefault       = 0.2
+	openAIWSPassthroughIdleTimeoutDefault = time.Hour

 	openAIWSStoreDisabledConnModeStrict   = "strict"
 	openAIWSStoreDisabledConnModeAdaptive = "adaptive"
@@ -904,6 +905,18 @@ func (s *OpenAIGatewayService) getOpenAIWSConnPool() *openAIWSConnPool {
 	return s.openaiWSPool
 }

+func (s *OpenAIGatewayService) getOpenAIWSPassthroughDialer() openAIWSClientDialer {
+	if s == nil {
+		return nil
+	}
+	s.openaiWSPassthroughDialerOnce.Do(func() {
+		if s.openaiWSPassthroughDialer == nil {
+			s.openaiWSPassthroughDialer = newDefaultOpenAIWSClientDialer()
+		}
+	})
+	return s.openaiWSPassthroughDialer
+}
+
 func (s *OpenAIGatewayService) SnapshotOpenAIWSPoolMetrics() OpenAIWSPoolMetricsSnapshot {
 	pool := s.getOpenAIWSConnPool()
 	if pool == nil {
@@ -967,6 +980,13 @@ func (s *OpenAIGatewayService) openAIWSReadTimeout() time.Duration {
 	return 15 * time.Minute
 }

+func (s *OpenAIGatewayService) openAIWSPassthroughIdleTimeout() time.Duration {
+	if timeout := s.openAIWSReadTimeout(); timeout > 0 {
+		return timeout
+	}
+	return openAIWSPassthroughIdleTimeoutDefault
+}
+
 func (s *OpenAIGatewayService) openAIWSWriteTimeout() time.Duration {
 	if s != nil && s.cfg != nil && s.cfg.Gateway.OpenAIWS.WriteTimeoutSeconds > 0 {
 		return time.Duration(s.cfg.Gateway.OpenAIWS.WriteTimeoutSeconds) * time.Second
@@ -2322,7 +2342,7 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(

 	wsDecision := s.getOpenAIWSProtocolResolver().Resolve(account)
 	modeRouterV2Enabled := s != nil && s.cfg != nil && s.cfg.Gateway.OpenAIWS.ModeRouterV2Enabled
-	ingressMode := OpenAIWSIngressModeShared
+	ingressMode := OpenAIWSIngressModeCtxPool
 	if modeRouterV2Enabled {
 		ingressMode = account.ResolveOpenAIResponsesWebSocketV2Mode(s.cfg.Gateway.OpenAIWS.IngressModeDefault)
 		if ingressMode == OpenAIWSIngressModeOff {
@@ -2332,6 +2352,30 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 				nil,
 			)
 		}
+		switch ingressMode {
+		case OpenAIWSIngressModePassthrough:
+			if wsDecision.Transport != OpenAIUpstreamTransportResponsesWebsocketV2 {
+				return fmt.Errorf("websocket ingress requires ws_v2 transport, got=%s", wsDecision.Transport)
+			}
+			return s.proxyResponsesWebSocketV2Passthrough(
+				ctx,
+				c,
+				clientConn,
+				account,
+				token,
+				firstClientMessage,
+				hooks,
+				wsDecision,
+			)
+		case OpenAIWSIngressModeCtxPool, OpenAIWSIngressModeShared, OpenAIWSIngressModeDedicated:
+			// continue
+		default:
+			return NewOpenAIWSClientCloseError(
+				coderws.StatusPolicyViolation,
+				"websocket mode only supports ctx_pool/passthrough",
+				nil,
+			)
+		}
 	}
 	if wsDecision.Transport != OpenAIUpstreamTransportResponsesWebsocketV2 {
 		return fmt.Errorf("websocket ingress requires ws_v2 transport, got=%s", wsDecision.Transport)
--- a/backend/internal/service/openai_ws_forwarder_ingress_session_test.go
+++ b/backend/internal/service/openai_ws_forwarder_ingress_session_test.go
@@ -149,7 +149,7 @@ func TestOpenAIGatewayService_ProxyResponsesWebSocketFromClient_KeepLeaseAcrossT
 	require.True(t, <-turnWSModeCh, "首轮 turn 应标记为 WS 模式")
 	require.True(t, <-turnWSModeCh, "第二轮 turn 应标记为 WS 模式")

-	require.NoError(t, clientConn.Close(coderws.StatusNormalClosure, "done"))
+	_ = clientConn.Close(coderws.StatusNormalClosure, "done")

 	select {
 	case serverErr := <-serverErrCh:
@@ -298,6 +298,140 @@ func TestOpenAIGatewayService_ProxyResponsesWebSocketFromClient_DedicatedModeDoe
 	require.Equal(t, 2, dialer.DialCount(), "dedicated 模式下跨客户端会话不应复用上游连接")
 }

+func TestOpenAIGatewayService_ProxyResponsesWebSocketFromClient_PassthroughModeRelaysByCaddyAdapter(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	cfg := &config.Config{}
+	cfg.Security.URLAllowlist.Enabled = false
+	cfg.Security.URLAllowlist.AllowInsecureHTTP = true
+	cfg.Gateway.OpenAIWS.Enabled = true
+	cfg.Gateway.OpenAIWS.OAuthEnabled = true
+	cfg.Gateway.OpenAIWS.APIKeyEnabled = true
+	cfg.Gateway.OpenAIWS.ResponsesWebsocketsV2 = true
+	cfg.Gateway.OpenAIWS.ModeRouterV2Enabled = true
+	cfg.Gateway.OpenAIWS.IngressModeDefault = OpenAIWSIngressModeCtxPool
+	cfg.Gateway.OpenAIWS.DialTimeoutSeconds = 3
+	cfg.Gateway.OpenAIWS.ReadTimeoutSeconds = 3
+	cfg.Gateway.OpenAIWS.WriteTimeoutSeconds = 3
+
+	upstreamConn := &openAIWSCaptureConn{
+		events: [][]byte{
+			[]byte(`{"type":"response.completed","response":{"id":"resp_passthrough_turn_1","model":"gpt-5.1","usage":{"input_tokens":2,"output_tokens":3}}}`),
+		},
+	}
+	captureDialer := &openAIWSCaptureDialer{conn: upstreamConn}
+	svc := &OpenAIGatewayService{
+		cfg:                       cfg,
+		httpUpstream:              &httpUpstreamRecorder{},
+		cache:                     &stubGatewayCache{},
+		openaiWSResolver:          NewOpenAIWSProtocolResolver(cfg),
+		toolCorrector:             NewCodexToolCorrector(),
+		openaiWSPassthroughDialer: captureDialer,
+	}
+
+	account := &Account{
+		ID:          452,
+		Name:        "openai-ingress-passthrough",
+		Platform:    PlatformOpenAI,
+		Type:        AccountTypeAPIKey,
+		Status:      StatusActive,
+		Schedulable: true,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"api_key": "sk-test",
+		},
+		Extra: map[string]any{
+			"openai_apikey_responses_websockets_v2_mode": OpenAIWSIngressModePassthrough,
+		},
+	}
+
+	serverErrCh := make(chan error, 1)
+	resultCh := make(chan *OpenAIForwardResult, 1)
+	hooks := &OpenAIWSIngressHooks{
+		AfterTurn: func(_ int, result *OpenAIForwardResult, turnErr error) {
+			if turnErr == nil && result != nil {
+				resultCh <- result
+			}
+		},
+	}
+
+	wsServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := coderws.Accept(w, r, &coderws.AcceptOptions{
+			CompressionMode: coderws.CompressionContextTakeover,
+		})
+		if err != nil {
+			serverErrCh <- err
+			return
+		}
+		defer func() {
+			_ = conn.CloseNow()
+		}()
+
+		rec := httptest.NewRecorder()
+		ginCtx, _ := gin.CreateTestContext(rec)
+		req := r.Clone(r.Context())
+		req.Header = req.Header.Clone()
+		req.Header.Set("User-Agent", "unit-test-agent/1.0")
+		ginCtx.Request = req
+
+		readCtx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
+		msgType, firstMessage, readErr := conn.Read(readCtx)
+		cancel()
+		if readErr != nil {
+			serverErrCh <- readErr
+			return
+		}
+		if msgType != coderws.MessageText && msgType != coderws.MessageBinary {
+			serverErrCh <- errors.New("unsupported websocket client message type")
+			return
+		}
+
+		serverErrCh <- svc.ProxyResponsesWebSocketFromClient(r.Context(), ginCtx, conn, account, "sk-test", firstMessage, hooks)
+	}))
+	defer wsServer.Close()
+
+	dialCtx, cancelDial := context.WithTimeout(context.Background(), 3*time.Second)
+	clientConn, _, err := coderws.Dial(dialCtx, "ws"+strings.TrimPrefix(wsServer.URL, "http"), nil)
+	cancelDial()
+	require.NoError(t, err)
+	defer func() {
+		_ = clientConn.CloseNow()
+	}()
+
+	writeCtx, cancelWrite := context.WithTimeout(context.Background(), 3*time.Second)
+	err = clientConn.Write(writeCtx, coderws.MessageText, []byte(`{"type":"response.create","model":"gpt-5.1","stream":false}`))
+	cancelWrite()
+	require.NoError(t, err)
+
+	readCtx, cancelRead := context.WithTimeout(context.Background(), 3*time.Second)
+	_, event, readErr := clientConn.Read(readCtx)
+	cancelRead()
+	require.NoError(t, readErr)
+	require.Equal(t, "response.completed", gjson.GetBytes(event, "type").String())
+	require.Equal(t, "resp_passthrough_turn_1", gjson.GetBytes(event, "response.id").String())
+	_ = clientConn.Close(coderws.StatusNormalClosure, "done")
+
+	select {
+	case serverErr := <-serverErrCh:
+		require.NoError(t, serverErr)
+	case <-time.After(5 * time.Second):
+		t.Fatal("等待 passthrough websocket 结束超时")
+	}
+
+	select {
+	case result := <-resultCh:
+		require.Equal(t, "resp_passthrough_turn_1", result.RequestID)
+		require.True(t, result.OpenAIWSMode)
+		require.Equal(t, 2, result.Usage.InputTokens)
+		require.Equal(t, 3, result.Usage.OutputTokens)
+	case <-time.After(2 * time.Second):
+		t.Fatal("未收到 passthrough turn 结果回调")
+	}
+
+	require.Equal(t, 1, captureDialer.DialCount(), "passthrough 模式应直接建立上游 websocket")
+	require.Len(t, upstreamConn.writes, 1, "passthrough 模式应透传首条 response.create")
+}
+
 func TestOpenAIGatewayService_ProxyResponsesWebSocketFromClient_ModeOffReturnsPolicyViolation(t *testing.T) {
 	gin.SetMode(gin.TestMode)

--- a/backend/internal/service/openai_ws_forwarder_success_test.go
+++ b/backend/internal/service/openai_ws_forwarder_success_test.go
@@ -15,6 +15,7 @@ import (
 	"time"

 	"github.com/Wei-Shaw/sub2api/internal/config"
+	coderws "github.com/coder/websocket"
 	"github.com/gin-gonic/gin"
 	"github.com/gorilla/websocket"
 	"github.com/stretchr/testify/require"
@@ -1282,6 +1283,18 @@ func (c *openAIWSCaptureConn) ReadMessage(ctx context.Context) ([]byte, error) {
 	return event, nil
 }

+func (c *openAIWSCaptureConn) ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error) {
+	payload, err := c.ReadMessage(ctx)
+	if err != nil {
+		return coderws.MessageText, nil, err
+	}
+	return coderws.MessageText, payload, nil
+}
+
+func (c *openAIWSCaptureConn) WriteFrame(ctx context.Context, _ coderws.MessageType, payload []byte) error {
+	return c.WriteJSON(ctx, json.RawMessage(payload))
+}
+
 func (c *openAIWSCaptureConn) Ping(ctx context.Context) error {
 	_ = ctx
 	return nil
--- a/backend/internal/service/openai_ws_protocol_resolver.go
+++ b/backend/internal/service/openai_ws_protocol_resolver.go
@@ -69,8 +69,11 @@ func (r *defaultOpenAIWSProtocolResolver) Resolve(account *Account) OpenAIWSProt
 		switch mode {
 		case OpenAIWSIngressModeOff:
 			return openAIWSHTTPDecision("account_mode_off")
-		case OpenAIWSIngressModeShared, OpenAIWSIngressModeDedicated:
+		case OpenAIWSIngressModeCtxPool, OpenAIWSIngressModePassthrough:
 			// continue
+		case OpenAIWSIngressModeShared, OpenAIWSIngressModeDedicated:
+			// 历史值兼容：按 ctx_pool 处理。
+			mode = OpenAIWSIngressModeCtxPool
 		default:
 			return openAIWSHTTPDecision("account_mode_off")
 		}
--- a/backend/internal/service/openai_ws_protocol_resolver_test.go
+++ b/backend/internal/service/openai_ws_protocol_resolver_test.go
@@ -143,21 +143,21 @@ func TestOpenAIWSProtocolResolver_Resolve_ModeRouterV2(t *testing.T) {
 	cfg.Gateway.OpenAIWS.APIKeyEnabled = true
 	cfg.Gateway.OpenAIWS.ResponsesWebsocketsV2 = true
 	cfg.Gateway.OpenAIWS.ModeRouterV2Enabled = true
-	cfg.Gateway.OpenAIWS.IngressModeDefault = OpenAIWSIngressModeShared
+	cfg.Gateway.OpenAIWS.IngressModeDefault = OpenAIWSIngressModeCtxPool

 	account := &Account{
 		Platform:    PlatformOpenAI,
 		Type:        AccountTypeOAuth,
 		Concurrency: 1,
 		Extra: map[string]any{
-			"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeDedicated,
+			"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeCtxPool,
 		},
 	}

-	t.Run("dedicated mode routes to ws v2", func(t *testing.T) {
+	t.Run("ctx_pool mode routes to ws v2", func(t *testing.T) {
 		decision := NewOpenAIWSProtocolResolver(cfg).Resolve(account)
 		require.Equal(t, OpenAIUpstreamTransportResponsesWebsocketV2, decision.Transport)
-		require.Equal(t, "ws_v2_mode_dedicated", decision.Reason)
+		require.Equal(t, "ws_v2_mode_ctx_pool", decision.Reason)
 	})

 	t.Run("off mode routes to http", func(t *testing.T) {
@@ -174,7 +174,7 @@ func TestOpenAIWSProtocolResolver_Resolve_ModeRouterV2(t *testing.T) {
 		require.Equal(t, "account_mode_off", decision.Reason)
 	})

-	t.Run("legacy boolean maps to shared in v2 router", func(t *testing.T) {
+	t.Run("legacy boolean maps to ctx_pool in v2 router", func(t *testing.T) {
 		legacyAccount := &Account{
 			Platform:    PlatformOpenAI,
 			Type:        AccountTypeAPIKey,
@@ -185,7 +185,21 @@ func TestOpenAIWSProtocolResolver_Resolve_ModeRouterV2(t *testing.T) {
 		}
 		decision := NewOpenAIWSProtocolResolver(cfg).Resolve(legacyAccount)
 		require.Equal(t, OpenAIUpstreamTransportResponsesWebsocketV2, decision.Transport)
-		require.Equal(t, "ws_v2_mode_shared", decision.Reason)
+		require.Equal(t, "ws_v2_mode_ctx_pool", decision.Reason)
+	})
+
+	t.Run("passthrough mode routes to ws v2", func(t *testing.T) {
+		passthroughAccount := &Account{
+			Platform:    PlatformOpenAI,
+			Type:        AccountTypeOAuth,
+			Concurrency: 1,
+			Extra: map[string]any{
+				"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModePassthrough,
+			},
+		}
+		decision := NewOpenAIWSProtocolResolver(cfg).Resolve(passthroughAccount)
+		require.Equal(t, OpenAIUpstreamTransportResponsesWebsocketV2, decision.Transport)
+		require.Equal(t, "ws_v2_mode_passthrough", decision.Reason)
 	})

 	t.Run("non-positive concurrency is rejected in v2 router", func(t *testing.T) {
@@ -193,7 +207,7 @@ func TestOpenAIWSProtocolResolver_Resolve_ModeRouterV2(t *testing.T) {
 			Platform: PlatformOpenAI,
 			Type:     AccountTypeOAuth,
 			Extra: map[string]any{
-				"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeShared,
+				"openai_oauth_responses_websockets_v2_mode": OpenAIWSIngressModeCtxPool,
 			},
 		}
 		decision := NewOpenAIWSProtocolResolver(cfg).Resolve(invalidConcurrency)
--- a/backend/internal/service/openai_ws_v2/caddy_adapter.go
+++ b/backend/internal/service/openai_ws_v2/caddy_adapter.go
@@ -0,0 +1,24 @@
+package openai_ws_v2
+
+import (
+	"context"
+)
+
+// runCaddyStyleRelay 采用 Caddy reverseproxy 的双向隧道思想：
+// 连接建立后并发复制两个方向，任一方向退出触发收敛关闭。
+//
+// Reference:
+// - Project: caddyserver/caddy (Apache-2.0)
+// - Commit: f283062d37c50627d53ca682ebae2ce219b35515
+// - Files:
+//   - modules/caddyhttp/reverseproxy/streaming.go
+//   - modules/caddyhttp/reverseproxy/reverseproxy.go
+func runCaddyStyleRelay(
+	ctx context.Context,
+	clientConn FrameConn,
+	upstreamConn FrameConn,
+	firstClientMessage []byte,
+	options RelayOptions,
+) (RelayResult, *RelayExit) {
+	return Relay(ctx, clientConn, upstreamConn, firstClientMessage, options)
+}
--- a/backend/internal/service/openai_ws_v2/entry.go
+++ b/backend/internal/service/openai_ws_v2/entry.go
@@ -0,0 +1,23 @@
+package openai_ws_v2
+
+import "context"
+
+// EntryInput 是 passthrough v2 数据面的入口参数。
+type EntryInput struct {
+	Ctx                context.Context
+	ClientConn         FrameConn
+	UpstreamConn       FrameConn
+	FirstClientMessage []byte
+	Options            RelayOptions
+}
+
+// RunEntry 是 openai_ws_v2 包对外的统一入口。
+func RunEntry(input EntryInput) (RelayResult, *RelayExit) {
+	return runCaddyStyleRelay(
+		input.Ctx,
+		input.ClientConn,
+		input.UpstreamConn,
+		input.FirstClientMessage,
+		input.Options,
+	)
+}
--- a/backend/internal/service/openai_ws_v2/metrics.go
+++ b/backend/internal/service/openai_ws_v2/metrics.go
@@ -0,0 +1,29 @@
+package openai_ws_v2
+
+import (
+	"sync/atomic"
+)
+
+// MetricsSnapshot 是 OpenAI WS v2 passthrough 路径的轻量运行时指标快照。
+type MetricsSnapshot struct {
+	SemanticMutationTotal  int64 `json:"semantic_mutation_total"`
+	UsageParseFailureTotal int64 `json:"usage_parse_failure_total"`
+}
+
+var (
+	// passthrough 路径默认不会做语义改写，该计数通常应保持为 0（保留用于未来防御性校验）。
+	passthroughSemanticMutationTotal  atomic.Int64
+	passthroughUsageParseFailureTotal atomic.Int64
+)
+
+func recordUsageParseFailure() {
+	passthroughUsageParseFailureTotal.Add(1)
+}
+
+// SnapshotMetrics 返回当前 passthrough 指标快照。
+func SnapshotMetrics() MetricsSnapshot {
+	return MetricsSnapshot{
+		SemanticMutationTotal:  passthroughSemanticMutationTotal.Load(),
+		UsageParseFailureTotal: passthroughUsageParseFailureTotal.Load(),
+	}
+}
--- a/backend/internal/service/openai_ws_v2/passthrough_relay.go
+++ b/backend/internal/service/openai_ws_v2/passthrough_relay.go
@@ -0,0 +1,807 @@
+package openai_ws_v2
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net"
+	"strconv"
+	"strings"
+	"sync/atomic"
+	"time"
+
+	coderws "github.com/coder/websocket"
+	"github.com/tidwall/gjson"
+)
+
+type FrameConn interface {
+	ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error)
+	WriteFrame(ctx context.Context, msgType coderws.MessageType, payload []byte) error
+	Close() error
+}
+
+type Usage struct {
+	InputTokens              int
+	OutputTokens             int
+	CacheCreationInputTokens int
+	CacheReadInputTokens     int
+}
+
+type RelayResult struct {
+	RequestModel            string
+	Usage                   Usage
+	RequestID               string
+	TerminalEventType       string
+	FirstTokenMs            *int
+	Duration                time.Duration
+	ClientToUpstreamFrames  int64
+	UpstreamToClientFrames  int64
+	DroppedDownstreamFrames int64
+}
+
+type RelayTurnResult struct {
+	RequestModel      string
+	Usage             Usage
+	RequestID         string
+	TerminalEventType string
+	Duration          time.Duration
+	FirstTokenMs      *int
+}
+
+type RelayExit struct {
+	Stage           string
+	Err             error
+	WroteDownstream bool
+}
+
+type RelayOptions struct {
+	WriteTimeout         time.Duration
+	IdleTimeout          time.Duration
+	UpstreamDrainTimeout time.Duration
+	FirstMessageType     coderws.MessageType
+	OnUsageParseFailure  func(eventType string, usageRaw string)
+	OnTurnComplete       func(turn RelayTurnResult)
+	OnTrace              func(event RelayTraceEvent)
+	Now                  func() time.Time
+}
+
+type RelayTraceEvent struct {
+	Stage           string
+	Direction       string
+	MessageType     string
+	PayloadBytes    int
+	Graceful        bool
+	WroteDownstream bool
+	Error           string
+}
+
+type relayState struct {
+	usage             Usage
+	requestModel      string
+	lastResponseID    string
+	terminalEventType string
+	firstTokenMs      *int
+	turnTimingByID    map[string]*relayTurnTiming
+}
+
+type relayExitSignal struct {
+	stage           string
+	err             error
+	graceful        bool
+	wroteDownstream bool
+}
+
+type observedUpstreamEvent struct {
+	terminal   bool
+	eventType  string
+	responseID string
+	usage      Usage
+	duration   time.Duration
+	firstToken *int
+}
+
+type relayTurnTiming struct {
+	startAt      time.Time
+	firstTokenMs *int
+}
+
+func Relay(
+	ctx context.Context,
+	clientConn FrameConn,
+	upstreamConn FrameConn,
+	firstClientMessage []byte,
+	options RelayOptions,
+) (RelayResult, *RelayExit) {
+	result := RelayResult{RequestModel: strings.TrimSpace(gjson.GetBytes(firstClientMessage, "model").String())}
+	if clientConn == nil || upstreamConn == nil {
+		return result, &RelayExit{Stage: "relay_init", Err: errors.New("relay connection is nil")}
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+
+	nowFn := options.Now
+	if nowFn == nil {
+		nowFn = time.Now
+	}
+	writeTimeout := options.WriteTimeout
+	if writeTimeout <= 0 {
+		writeTimeout = 2 * time.Minute
+	}
+	drainTimeout := options.UpstreamDrainTimeout
+	if drainTimeout <= 0 {
+		drainTimeout = 1200 * time.Millisecond
+	}
+	firstMessageType := options.FirstMessageType
+	if firstMessageType != coderws.MessageBinary {
+		firstMessageType = coderws.MessageText
+	}
+	startAt := nowFn()
+	state := &relayState{requestModel: result.RequestModel}
+	onTrace := options.OnTrace
+
+	relayCtx, relayCancel := context.WithCancel(ctx)
+	defer relayCancel()
+
+	lastActivity := atomic.Int64{}
+	lastActivity.Store(nowFn().UnixNano())
+	markActivity := func() {
+		lastActivity.Store(nowFn().UnixNano())
+	}
+
+	writeUpstream := func(msgType coderws.MessageType, payload []byte) error {
+		writeCtx, cancel := context.WithTimeout(relayCtx, writeTimeout)
+		defer cancel()
+		return upstreamConn.WriteFrame(writeCtx, msgType, payload)
+	}
+	writeClient := func(msgType coderws.MessageType, payload []byte) error {
+		writeCtx, cancel := context.WithTimeout(relayCtx, writeTimeout)
+		defer cancel()
+		return clientConn.WriteFrame(writeCtx, msgType, payload)
+	}
+
+	clientToUpstreamFrames := &atomic.Int64{}
+	upstreamToClientFrames := &atomic.Int64{}
+	droppedDownstreamFrames := &atomic.Int64{}
+	emitRelayTrace(onTrace, RelayTraceEvent{
+		Stage:        "relay_start",
+		PayloadBytes: len(firstClientMessage),
+		MessageType:  relayMessageTypeString(firstMessageType),
+	})
+
+	if err := writeUpstream(firstMessageType, firstClientMessage); err != nil {
+		result.Duration = nowFn().Sub(startAt)
+		emitRelayTrace(onTrace, RelayTraceEvent{
+			Stage:        "write_first_message_failed",
+			Direction:    "client_to_upstream",
+			MessageType:  relayMessageTypeString(firstMessageType),
+			PayloadBytes: len(firstClientMessage),
+			Error:        err.Error(),
+		})
+		return result, &RelayExit{Stage: "write_upstream", Err: err}
+	}
+	clientToUpstreamFrames.Add(1)
+	emitRelayTrace(onTrace, RelayTraceEvent{
+		Stage:        "write_first_message_ok",
+		Direction:    "client_to_upstream",
+		MessageType:  relayMessageTypeString(firstMessageType),
+		PayloadBytes: len(firstClientMessage),
+	})
+	markActivity()
+
+	exitCh := make(chan relayExitSignal, 3)
+	dropDownstreamWrites := atomic.Bool{}
+	go runClientToUpstream(relayCtx, clientConn, writeUpstream, markActivity, clientToUpstreamFrames, onTrace, exitCh)
+	go runUpstreamToClient(
+		relayCtx,
+		upstreamConn,
+		writeClient,
+		startAt,
+		nowFn,
+		state,
+		options.OnUsageParseFailure,
+		options.OnTurnComplete,
+		&dropDownstreamWrites,
+		upstreamToClientFrames,
+		droppedDownstreamFrames,
+		markActivity,
+		onTrace,
+		exitCh,
+	)
+	go runIdleWatchdog(relayCtx, nowFn, options.IdleTimeout, &lastActivity, onTrace, exitCh)
+
+	firstExit := <-exitCh
+	emitRelayTrace(onTrace, RelayTraceEvent{
+		Stage:           "first_exit",
+		Direction:       relayDirectionFromStage(firstExit.stage),
+		Graceful:        firstExit.graceful,
+		WroteDownstream: firstExit.wroteDownstream,
+		Error:           relayErrorString(firstExit.err),
+	})
+	combinedWroteDownstream := firstExit.wroteDownstream
+	secondExit := relayExitSignal{graceful: true}
+	hasSecondExit := false
+
+	// 客户端断开后尽力继续读取上游短窗口，捕获延迟 usage/terminal 事件用于计费。
+	if firstExit.stage == "read_client" && firstExit.graceful {
+		dropDownstreamWrites.Store(true)
+		secondExit, hasSecondExit = waitRelayExit(exitCh, drainTimeout)
+	} else {
+		relayCancel()
+		_ = upstreamConn.Close()
+		secondExit, hasSecondExit = waitRelayExit(exitCh, 200*time.Millisecond)
+	}
+	if hasSecondExit {
+		combinedWroteDownstream = combinedWroteDownstream || secondExit.wroteDownstream
+		emitRelayTrace(onTrace, RelayTraceEvent{
+			Stage:           "second_exit",
+			Direction:       relayDirectionFromStage(secondExit.stage),
+			Graceful:        secondExit.graceful,
+			WroteDownstream: secondExit.wroteDownstream,
+			Error:           relayErrorString(secondExit.err),
+		})
+	}
+
+	relayCancel()
+	_ = upstreamConn.Close()
+
+	enrichResult(&result, state, nowFn().Sub(startAt))
+	result.ClientToUpstreamFrames = clientToUpstreamFrames.Load()
+	result.UpstreamToClientFrames = upstreamToClientFrames.Load()
+	result.DroppedDownstreamFrames = droppedDownstreamFrames.Load()
+	if firstExit.stage == "read_client" && firstExit.graceful {
+		stage := "client_disconnected"
+		exitErr := firstExit.err
+		if hasSecondExit && !secondExit.graceful {
+			stage = secondExit.stage
+			exitErr = secondExit.err
+		}
+		if exitErr == nil {
+			exitErr = io.EOF
+		}
+		emitRelayTrace(onTrace, RelayTraceEvent{
+			Stage:           "relay_exit",
+			Direction:       relayDirectionFromStage(stage),
+			Graceful:        false,
+			WroteDownstream: combinedWroteDownstream,
+			Error:           relayErrorString(exitErr),
+		})
+		return result, &RelayExit{
+			Stage:           stage,
+			Err:             exitErr,
+			WroteDownstream: combinedWroteDownstream,
+		}
+	}
+	if firstExit.graceful && (!hasSecondExit || secondExit.graceful) {
+		emitRelayTrace(onTrace, RelayTraceEvent{
+			Stage:           "relay_complete",
+			Graceful:        true,
+			WroteDownstream: combinedWroteDownstream,
+		})
+		_ = clientConn.Close()
+		return result, nil
+	}
+	if !firstExit.graceful {
+		emitRelayTrace(onTrace, RelayTraceEvent{
+			Stage:           "relay_exit",
+			Direction:       relayDirectionFromStage(firstExit.stage),
+			Graceful:        false,
+			WroteDownstream: combinedWroteDownstream,
+			Error:           relayErrorString(firstExit.err),
+		})
+		return result, &RelayExit{
+			Stage:           firstExit.stage,
+			Err:             firstExit.err,
+			WroteDownstream: combinedWroteDownstream,
+		}
+	}
+	if hasSecondExit && !secondExit.graceful {
+		emitRelayTrace(onTrace, RelayTraceEvent{
+			Stage:           "relay_exit",
+			Direction:       relayDirectionFromStage(secondExit.stage),
+			Graceful:        false,
+			WroteDownstream: combinedWroteDownstream,
+			Error:           relayErrorString(secondExit.err),
+		})
+		return result, &RelayExit{
+			Stage:           secondExit.stage,
+			Err:             secondExit.err,
+			WroteDownstream: combinedWroteDownstream,
+		}
+	}
+	emitRelayTrace(onTrace, RelayTraceEvent{
+		Stage:           "relay_complete",
+		Graceful:        true,
+		WroteDownstream: combinedWroteDownstream,
+	})
+	_ = clientConn.Close()
+	return result, nil
+}
+
+func runClientToUpstream(
+	ctx context.Context,
+	clientConn FrameConn,
+	writeUpstream func(msgType coderws.MessageType, payload []byte) error,
+	markActivity func(),
+	forwardedFrames *atomic.Int64,
+	onTrace func(event RelayTraceEvent),
+	exitCh chan<- relayExitSignal,
+) {
+	for {
+		msgType, payload, err := clientConn.ReadFrame(ctx)
+		if err != nil {
+			emitRelayTrace(onTrace, RelayTraceEvent{
+				Stage:     "read_client_failed",
+				Direction: "client_to_upstream",
+				Error:     err.Error(),
+				Graceful:  isDisconnectError(err),
+			})
+			exitCh <- relayExitSignal{stage: "read_client", err: err, graceful: isDisconnectError(err)}
+			return
+		}
+		markActivity()
+		if err := writeUpstream(msgType, payload); err != nil {
+			emitRelayTrace(onTrace, RelayTraceEvent{
+				Stage:        "write_upstream_failed",
+				Direction:    "client_to_upstream",
+				MessageType:  relayMessageTypeString(msgType),
+				PayloadBytes: len(payload),
+				Error:        err.Error(),
+			})
+			exitCh <- relayExitSignal{stage: "write_upstream", err: err}
+			return
+		}
+		if forwardedFrames != nil {
+			forwardedFrames.Add(1)
+		}
+		markActivity()
+	}
+}
+
+func runUpstreamToClient(
+	ctx context.Context,
+	upstreamConn FrameConn,
+	writeClient func(msgType coderws.MessageType, payload []byte) error,
+	startAt time.Time,
+	nowFn func() time.Time,
+	state *relayState,
+	onUsageParseFailure func(eventType string, usageRaw string),
+	onTurnComplete func(turn RelayTurnResult),
+	dropDownstreamWrites *atomic.Bool,
+	forwardedFrames *atomic.Int64,
+	droppedFrames *atomic.Int64,
+	markActivity func(),
+	onTrace func(event RelayTraceEvent),
+	exitCh chan<- relayExitSignal,
+) {
+	wroteDownstream := false
+	for {
+		msgType, payload, err := upstreamConn.ReadFrame(ctx)
+		if err != nil {
+			emitRelayTrace(onTrace, RelayTraceEvent{
+				Stage:           "read_upstream_failed",
+				Direction:       "upstream_to_client",
+				Error:           err.Error(),
+				Graceful:        isDisconnectError(err),
+				WroteDownstream: wroteDownstream,
+			})
+			exitCh <- relayExitSignal{
+				stage:           "read_upstream",
+				err:             err,
+				graceful:        isDisconnectError(err),
+				wroteDownstream: wroteDownstream,
+			}
+			return
+		}
+		markActivity()
+		observedEvent := observedUpstreamEvent{}
+		switch msgType {
+		case coderws.MessageText:
+			observedEvent = observeUpstreamMessage(state, payload, startAt, nowFn, onUsageParseFailure)
+		case coderws.MessageBinary:
+			// binary frame 直接透传，不进入 JSON 观测路径（避免无效解析开销）。
+		}
+		emitTurnComplete(onTurnComplete, state, observedEvent)
+		if dropDownstreamWrites != nil && dropDownstreamWrites.Load() {
+			if droppedFrames != nil {
+				droppedFrames.Add(1)
+			}
+			emitRelayTrace(onTrace, RelayTraceEvent{
+				Stage:           "drop_downstream_frame",
+				Direction:       "upstream_to_client",
+				MessageType:     relayMessageTypeString(msgType),
+				PayloadBytes:    len(payload),
+				WroteDownstream: wroteDownstream,
+			})
+			if observedEvent.terminal {
+				exitCh <- relayExitSignal{
+					stage:           "drain_terminal",
+					graceful:        true,
+					wroteDownstream: wroteDownstream,
+				}
+				return
+			}
+			markActivity()
+			continue
+		}
+		if err := writeClient(msgType, payload); err != nil {
+			emitRelayTrace(onTrace, RelayTraceEvent{
+				Stage:           "write_client_failed",
+				Direction:       "upstream_to_client",
+				MessageType:     relayMessageTypeString(msgType),
+				PayloadBytes:    len(payload),
+				WroteDownstream: wroteDownstream,
+				Error:           err.Error(),
+			})
+			exitCh <- relayExitSignal{stage: "write_client", err: err, wroteDownstream: wroteDownstream}
+			return
+		}
+		wroteDownstream = true
+		if forwardedFrames != nil {
+			forwardedFrames.Add(1)
+		}
+		markActivity()
+	}
+}
+
+func runIdleWatchdog(
+	ctx context.Context,
+	nowFn func() time.Time,
+	idleTimeout time.Duration,
+	lastActivity *atomic.Int64,
+	onTrace func(event RelayTraceEvent),
+	exitCh chan<- relayExitSignal,
+) {
+	if idleTimeout <= 0 {
+		return
+	}
+	checkInterval := minDuration(idleTimeout/4, 5*time.Second)
+	if checkInterval < time.Second {
+		checkInterval = time.Second
+	}
+	ticker := time.NewTicker(checkInterval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			last := time.Unix(0, lastActivity.Load())
+			if nowFn().Sub(last) < idleTimeout {
+				continue
+			}
+			emitRelayTrace(onTrace, RelayTraceEvent{
+				Stage:     "idle_timeout_triggered",
+				Direction: "watchdog",
+				Error:     context.DeadlineExceeded.Error(),
+			})
+			exitCh <- relayExitSignal{stage: "idle_timeout", err: context.DeadlineExceeded}
+			return
+		}
+	}
+}
+
+func emitRelayTrace(onTrace func(event RelayTraceEvent), event RelayTraceEvent) {
+	if onTrace == nil {
+		return
+	}
+	onTrace(event)
+}
+
+func relayMessageTypeString(msgType coderws.MessageType) string {
+	switch msgType {
+	case coderws.MessageText:
+		return "text"
+	case coderws.MessageBinary:
+		return "binary"
+	default:
+		return "unknown(" + strconv.Itoa(int(msgType)) + ")"
+	}
+}
+
+func relayDirectionFromStage(stage string) string {
+	switch stage {
+	case "read_client", "write_upstream":
+		return "client_to_upstream"
+	case "read_upstream", "write_client", "drain_terminal":
+		return "upstream_to_client"
+	case "idle_timeout":
+		return "watchdog"
+	default:
+		return ""
+	}
+}
+
+func relayErrorString(err error) string {
+	if err == nil {
+		return ""
+	}
+	return err.Error()
+}
+
+func observeUpstreamMessage(
+	state *relayState,
+	message []byte,
+	startAt time.Time,
+	nowFn func() time.Time,
+	onUsageParseFailure func(eventType string, usageRaw string),
+) observedUpstreamEvent {
+	if state == nil || len(message) == 0 {
+		return observedUpstreamEvent{}
+	}
+	values := gjson.GetManyBytes(message, "type", "response.id", "response_id", "id")
+	eventType := strings.TrimSpace(values[0].String())
+	if eventType == "" {
+		return observedUpstreamEvent{}
+	}
+	responseID := strings.TrimSpace(values[1].String())
+	if responseID == "" {
+		responseID = strings.TrimSpace(values[2].String())
+	}
+	// 仅 terminal 事件兜底读取顶层 id，避免把 event_id 当成 response_id 关联到 turn。
+	if responseID == "" && isTerminalEvent(eventType) {
+		responseID = strings.TrimSpace(values[3].String())
+	}
+	now := nowFn()
+
+	if state.firstTokenMs == nil && isTokenEvent(eventType) {
+		ms := int(now.Sub(startAt).Milliseconds())
+		if ms >= 0 {
+			state.firstTokenMs = &ms
+		}
+	}
+	parsedUsage := parseUsageAndAccumulate(state, message, eventType, onUsageParseFailure)
+	observed := observedUpstreamEvent{
+		eventType:  eventType,
+		responseID: responseID,
+		usage:      parsedUsage,
+	}
+	if responseID != "" {
+		turnTiming := openAIWSRelayGetOrInitTurnTiming(state, responseID, now)
+		if turnTiming != nil && turnTiming.firstTokenMs == nil && isTokenEvent(eventType) {
+			ms := int(now.Sub(turnTiming.startAt).Milliseconds())
+			if ms >= 0 {
+				turnTiming.firstTokenMs = &ms
+			}
+		}
+	}
+	if !isTerminalEvent(eventType) {
+		return observed
+	}
+	observed.terminal = true
+	state.terminalEventType = eventType
+	if responseID != "" {
+		state.lastResponseID = responseID
+		if turnTiming, ok := openAIWSRelayDeleteTurnTiming(state, responseID); ok {
+			duration := now.Sub(turnTiming.startAt)
+			if duration < 0 {
+				duration = 0
+			}
+			observed.duration = duration
+			observed.firstToken = openAIWSRelayCloneIntPtr(turnTiming.firstTokenMs)
+		}
+	}
+	return observed
+}
+
+func emitTurnComplete(
+	onTurnComplete func(turn RelayTurnResult),
+	state *relayState,
+	observed observedUpstreamEvent,
+) {
+	if onTurnComplete == nil || !observed.terminal {
+		return
+	}
+	responseID := strings.TrimSpace(observed.responseID)
+	if responseID == "" {
+		return
+	}
+	requestModel := ""
+	if state != nil {
+		requestModel = state.requestModel
+	}
+	onTurnComplete(RelayTurnResult{
+		RequestModel:      requestModel,
+		Usage:             observed.usage,
+		RequestID:         responseID,
+		TerminalEventType: observed.eventType,
+		Duration:          observed.duration,
+		FirstTokenMs:      openAIWSRelayCloneIntPtr(observed.firstToken),
+	})
+}
+
+func openAIWSRelayGetOrInitTurnTiming(state *relayState, responseID string, now time.Time) *relayTurnTiming {
+	if state == nil {
+		return nil
+	}
+	if state.turnTimingByID == nil {
+		state.turnTimingByID = make(map[string]*relayTurnTiming, 8)
+	}
+	timing, ok := state.turnTimingByID[responseID]
+	if !ok || timing == nil || timing.startAt.IsZero() {
+		timing = &relayTurnTiming{startAt: now}
+		state.turnTimingByID[responseID] = timing
+		return timing
+	}
+	return timing
+}
+
+func openAIWSRelayDeleteTurnTiming(state *relayState, responseID string) (relayTurnTiming, bool) {
+	if state == nil || state.turnTimingByID == nil {
+		return relayTurnTiming{}, false
+	}
+	timing, ok := state.turnTimingByID[responseID]
+	if !ok || timing == nil {
+		return relayTurnTiming{}, false
+	}
+	delete(state.turnTimingByID, responseID)
+	return *timing, true
+}
+
+func openAIWSRelayCloneIntPtr(v *int) *int {
+	if v == nil {
+		return nil
+	}
+	cloned := *v
+	return &cloned
+}
+
+func parseUsageAndAccumulate(
+	state *relayState,
+	message []byte,
+	eventType string,
+	onParseFailure func(eventType string, usageRaw string),
+) Usage {
+	if state == nil || len(message) == 0 || !shouldParseUsage(eventType) {
+		return Usage{}
+	}
+	usageResult := gjson.GetBytes(message, "response.usage")
+	if !usageResult.Exists() {
+		return Usage{}
+	}
+	usageRaw := strings.TrimSpace(usageResult.Raw)
+	if usageRaw == "" || !strings.HasPrefix(usageRaw, "{") {
+		recordUsageParseFailure()
+		if onParseFailure != nil {
+			onParseFailure(eventType, usageRaw)
+		}
+		return Usage{}
+	}
+
+	inputResult := gjson.GetBytes(message, "response.usage.input_tokens")
+	outputResult := gjson.GetBytes(message, "response.usage.output_tokens")
+	cachedResult := gjson.GetBytes(message, "response.usage.input_tokens_details.cached_tokens")
+
+	inputTokens, inputOK := parseUsageIntField(inputResult, true)
+	outputTokens, outputOK := parseUsageIntField(outputResult, true)
+	cachedTokens, cachedOK := parseUsageIntField(cachedResult, false)
+	if !inputOK || !outputOK || !cachedOK {
+		recordUsageParseFailure()
+		if onParseFailure != nil {
+			onParseFailure(eventType, usageRaw)
+		}
+		// 解析失败时不做部分字段累加，避免计费 usage 出现“半有效”状态。
+		return Usage{}
+	}
+	parsedUsage := Usage{
+		InputTokens:          inputTokens,
+		OutputTokens:         outputTokens,
+		CacheReadInputTokens: cachedTokens,
+	}
+
+	state.usage.InputTokens += parsedUsage.InputTokens
+	state.usage.OutputTokens += parsedUsage.OutputTokens
+	state.usage.CacheReadInputTokens += parsedUsage.CacheReadInputTokens
+	return parsedUsage
+}
+
+func parseUsageIntField(value gjson.Result, required bool) (int, bool) {
+	if !value.Exists() {
+		return 0, !required
+	}
+	if value.Type != gjson.Number {
+		return 0, false
+	}
+	return int(value.Int()), true
+}
+
+func enrichResult(result *RelayResult, state *relayState, duration time.Duration) {
+	if result == nil {
+		return
+	}
+	result.Duration = duration
+	if state == nil {
+		return
+	}
+	result.RequestModel = state.requestModel
+	result.Usage = state.usage
+	result.RequestID = state.lastResponseID
+	result.TerminalEventType = state.terminalEventType
+	result.FirstTokenMs = state.firstTokenMs
+}
+
+func isDisconnectError(err error) bool {
+	if err == nil {
+		return false
+	}
+	if errors.Is(err, io.EOF) || errors.Is(err, net.ErrClosed) || errors.Is(err, context.Canceled) {
+		return true
+	}
+	switch coderws.CloseStatus(err) {
+	case coderws.StatusNormalClosure, coderws.StatusGoingAway, coderws.StatusNoStatusRcvd, coderws.StatusAbnormalClosure:
+		return true
+	}
+	message := strings.ToLower(strings.TrimSpace(err.Error()))
+	if message == "" {
+		return false
+	}
+	return strings.Contains(message, "failed to read frame header: eof") ||
+		strings.Contains(message, "unexpected eof") ||
+		strings.Contains(message, "use of closed network connection") ||
+		strings.Contains(message, "connection reset by peer") ||
+		strings.Contains(message, "broken pipe")
+}
+
+func isTerminalEvent(eventType string) bool {
+	switch eventType {
+	case "response.completed", "response.done", "response.failed", "response.incomplete", "response.cancelled", "response.canceled":
+		return true
+	default:
+		return false
+	}
+}
+
+func shouldParseUsage(eventType string) bool {
+	switch eventType {
+	case "response.completed", "response.done", "response.failed":
+		return true
+	default:
+		return false
+	}
+}
+
+func isTokenEvent(eventType string) bool {
+	if eventType == "" {
+		return false
+	}
+	switch eventType {
+	case "response.created", "response.in_progress", "response.output_item.added", "response.output_item.done":
+		return false
+	}
+	if strings.Contains(eventType, ".delta") {
+		return true
+	}
+	if strings.HasPrefix(eventType, "response.output_text") {
+		return true
+	}
+	if strings.HasPrefix(eventType, "response.output") {
+		return true
+	}
+	return eventType == "response.completed" || eventType == "response.done"
+}
+
+func minDuration(a, b time.Duration) time.Duration {
+	if a <= 0 {
+		return b
+	}
+	if b <= 0 {
+		return a
+	}
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func waitRelayExit(exitCh <-chan relayExitSignal, timeout time.Duration) (relayExitSignal, bool) {
+	if timeout <= 0 {
+		timeout = 200 * time.Millisecond
+	}
+	select {
+	case sig := <-exitCh:
+		return sig, true
+	case <-time.After(timeout):
+		return relayExitSignal{}, false
+	}
+}
--- a/backend/internal/service/openai_ws_v2/passthrough_relay_internal_test.go
+++ b/backend/internal/service/openai_ws_v2/passthrough_relay_internal_test.go
@@ -0,0 +1,432 @@
+package openai_ws_v2
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	coderws "github.com/coder/websocket"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestRunEntry_DelegatesRelay(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_entry","usage":{"input_tokens":1,"output_tokens":1}}}`),
+		},
+	}, true)
+
+	result, relayExit := RunEntry(EntryInput{
+		Ctx:                context.Background(),
+		ClientConn:         clientConn,
+		UpstreamConn:       upstreamConn,
+		FirstClientMessage: []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`),
+	})
+	require.Nil(t, relayExit)
+	require.Equal(t, "resp_entry", result.RequestID)
+}
+
+func TestRunClientToUpstream_ErrorPaths(t *testing.T) {
+	t.Parallel()
+
+	t.Run("read client eof", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		runClientToUpstream(
+			context.Background(),
+			newPassthroughTestFrameConn(nil, true),
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			func() {},
+			nil,
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "read_client", sig.stage)
+		require.True(t, sig.graceful)
+	})
+
+	t.Run("write upstream failed", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		runClientToUpstream(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{msgType: coderws.MessageText, payload: []byte(`{"x":1}`)},
+			}, true),
+			func(_ coderws.MessageType, _ []byte) error { return errors.New("boom") },
+			func() {},
+			nil,
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "write_upstream", sig.stage)
+		require.False(t, sig.graceful)
+	})
+
+	t.Run("forwarded counter and trace callback", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		forwarded := &atomic.Int64{}
+		traces := make([]RelayTraceEvent, 0, 2)
+		runClientToUpstream(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{msgType: coderws.MessageText, payload: []byte(`{"x":1}`)},
+			}, true),
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			func() {},
+			forwarded,
+			func(event RelayTraceEvent) {
+				traces = append(traces, event)
+			},
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "read_client", sig.stage)
+		require.Equal(t, int64(1), forwarded.Load())
+		require.NotEmpty(t, traces)
+	})
+}
+
+func TestRunUpstreamToClient_ErrorAndDropPaths(t *testing.T) {
+	t.Parallel()
+
+	t.Run("read upstream eof", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		drop := &atomic.Bool{}
+		drop.Store(false)
+		runUpstreamToClient(
+			context.Background(),
+			newPassthroughTestFrameConn(nil, true),
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			time.Now(),
+			time.Now,
+			&relayState{},
+			nil,
+			nil,
+			drop,
+			nil,
+			nil,
+			func() {},
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "read_upstream", sig.stage)
+		require.True(t, sig.graceful)
+	})
+
+	t.Run("write client failed", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		drop := &atomic.Bool{}
+		drop.Store(false)
+		runUpstreamToClient(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{msgType: coderws.MessageText, payload: []byte(`{"type":"response.output_text.delta","delta":"x"}`)},
+			}, true),
+			func(_ coderws.MessageType, _ []byte) error { return errors.New("write failed") },
+			time.Now(),
+			time.Now,
+			&relayState{},
+			nil,
+			nil,
+			drop,
+			nil,
+			nil,
+			func() {},
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "write_client", sig.stage)
+	})
+
+	t.Run("drop downstream and stop on terminal", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		drop := &atomic.Bool{}
+		drop.Store(true)
+		dropped := &atomic.Int64{}
+		runUpstreamToClient(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{
+					msgType: coderws.MessageText,
+					payload: []byte(`{"type":"response.completed","response":{"id":"resp_drop","usage":{"input_tokens":1,"output_tokens":1}}}`),
+				},
+			}, true),
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			time.Now(),
+			time.Now,
+			&relayState{},
+			nil,
+			nil,
+			drop,
+			nil,
+			dropped,
+			func() {},
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "drain_terminal", sig.stage)
+		require.True(t, sig.graceful)
+		require.Equal(t, int64(1), dropped.Load())
+	})
+}
+
+func TestRunIdleWatchdog_NoTimeoutWhenDisabled(t *testing.T) {
+	t.Parallel()
+
+	exitCh := make(chan relayExitSignal, 1)
+	lastActivity := &atomic.Int64{}
+	lastActivity.Store(time.Now().UnixNano())
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go runIdleWatchdog(ctx, time.Now, 0, lastActivity, nil, exitCh)
+	select {
+	case <-exitCh:
+		t.Fatal("unexpected idle timeout signal")
+	case <-time.After(200 * time.Millisecond):
+	}
+}
+
+func TestHelperFunctionsCoverage(t *testing.T) {
+	t.Parallel()
+
+	require.Equal(t, "text", relayMessageTypeString(coderws.MessageText))
+	require.Equal(t, "binary", relayMessageTypeString(coderws.MessageBinary))
+	require.Contains(t, relayMessageTypeString(coderws.MessageType(99)), "unknown(")
+
+	require.Equal(t, "", relayErrorString(nil))
+	require.Equal(t, "x", relayErrorString(errors.New("x")))
+
+	require.True(t, isDisconnectError(io.EOF))
+	require.True(t, isDisconnectError(net.ErrClosed))
+	require.True(t, isDisconnectError(context.Canceled))
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusGoingAway}))
+	require.True(t, isDisconnectError(errors.New("broken pipe")))
+	require.False(t, isDisconnectError(errors.New("unrelated")))
+
+	require.True(t, isTokenEvent("response.output_text.delta"))
+	require.True(t, isTokenEvent("response.output_audio.delta"))
+	require.True(t, isTokenEvent("response.completed"))
+	require.False(t, isTokenEvent(""))
+	require.False(t, isTokenEvent("response.created"))
+
+	require.Equal(t, 2*time.Second, minDuration(2*time.Second, 5*time.Second))
+	require.Equal(t, 2*time.Second, minDuration(5*time.Second, 2*time.Second))
+	require.Equal(t, 5*time.Second, minDuration(0, 5*time.Second))
+	require.Equal(t, 2*time.Second, minDuration(2*time.Second, 0))
+
+	ch := make(chan relayExitSignal, 1)
+	ch <- relayExitSignal{stage: "ok"}
+	sig, ok := waitRelayExit(ch, 10*time.Millisecond)
+	require.True(t, ok)
+	require.Equal(t, "ok", sig.stage)
+	ch <- relayExitSignal{stage: "ok2"}
+	sig, ok = waitRelayExit(ch, 0)
+	require.True(t, ok)
+	require.Equal(t, "ok2", sig.stage)
+	_, ok = waitRelayExit(ch, 10*time.Millisecond)
+	require.False(t, ok)
+
+	n, ok := parseUsageIntField(gjson.Get(`{"n":3}`, "n"), true)
+	require.True(t, ok)
+	require.Equal(t, 3, n)
+	_, ok = parseUsageIntField(gjson.Get(`{"n":"x"}`, "n"), true)
+	require.False(t, ok)
+	n, ok = parseUsageIntField(gjson.Result{}, false)
+	require.True(t, ok)
+	require.Equal(t, 0, n)
+	_, ok = parseUsageIntField(gjson.Result{}, true)
+	require.False(t, ok)
+}
+
+func TestParseUsageAndEnrichCoverage(t *testing.T) {
+	t.Parallel()
+
+	state := &relayState{}
+	parseUsageAndAccumulate(state, []byte(`{"type":"response.completed","response":{"usage":{"input_tokens":"bad"}}}`), "response.completed", nil)
+	require.Equal(t, 0, state.usage.InputTokens)
+
+	parseUsageAndAccumulate(
+		state,
+		[]byte(`{"type":"response.completed","response":{"usage":{"input_tokens":9,"output_tokens":"bad","input_tokens_details":{"cached_tokens":2}}}}`),
+		"response.completed",
+		nil,
+	)
+	require.Equal(t, 0, state.usage.InputTokens, "部分字段解析失败时不应累加 usage")
+	require.Equal(t, 0, state.usage.OutputTokens)
+	require.Equal(t, 0, state.usage.CacheReadInputTokens)
+
+	parseUsageAndAccumulate(
+		state,
+		[]byte(`{"type":"response.completed","response":{"usage":{"input_tokens_details":{"cached_tokens":2}}}}`),
+		"response.completed",
+		nil,
+	)
+	require.Equal(t, 0, state.usage.InputTokens, "必填 usage 字段缺失时不应累加 usage")
+	require.Equal(t, 0, state.usage.OutputTokens)
+	require.Equal(t, 0, state.usage.CacheReadInputTokens)
+
+	parseUsageAndAccumulate(state, []byte(`{"type":"response.completed","response":{"usage":{"input_tokens":2,"output_tokens":1,"input_tokens_details":{"cached_tokens":1}}}}`), "response.completed", nil)
+	require.Equal(t, 2, state.usage.InputTokens)
+	require.Equal(t, 1, state.usage.OutputTokens)
+	require.Equal(t, 1, state.usage.CacheReadInputTokens)
+
+	result := &RelayResult{}
+	enrichResult(result, state, 5*time.Millisecond)
+	require.Equal(t, state.usage.InputTokens, result.Usage.InputTokens)
+	require.Equal(t, 5*time.Millisecond, result.Duration)
+	parseUsageAndAccumulate(state, []byte(`{"type":"response.in_progress","response":{"usage":{"input_tokens":9}}}`), "response.in_progress", nil)
+	require.Equal(t, 2, state.usage.InputTokens)
+	enrichResult(nil, state, 0)
+}
+
+func TestEmitTurnCompleteCoverage(t *testing.T) {
+	t.Parallel()
+
+	// 非 terminal 事件不应触发。
+	called := 0
+	emitTurnComplete(func(turn RelayTurnResult) {
+		called++
+	}, &relayState{requestModel: "gpt-5"}, observedUpstreamEvent{
+		terminal:   false,
+		eventType:  "response.output_text.delta",
+		responseID: "resp_ignored",
+		usage:      Usage{InputTokens: 1},
+	})
+	require.Equal(t, 0, called)
+
+	// 缺少 response_id 时不应触发。
+	emitTurnComplete(func(turn RelayTurnResult) {
+		called++
+	}, &relayState{requestModel: "gpt-5"}, observedUpstreamEvent{
+		terminal:  true,
+		eventType: "response.completed",
+	})
+	require.Equal(t, 0, called)
+
+	// terminal 且 response_id 存在，应该触发；state=nil 时 model 为空串。
+	var got RelayTurnResult
+	emitTurnComplete(func(turn RelayTurnResult) {
+		called++
+		got = turn
+	}, nil, observedUpstreamEvent{
+		terminal:   true,
+		eventType:  "response.completed",
+		responseID: "resp_emit",
+		usage:      Usage{InputTokens: 2, OutputTokens: 3},
+	})
+	require.Equal(t, 1, called)
+	require.Equal(t, "resp_emit", got.RequestID)
+	require.Equal(t, "response.completed", got.TerminalEventType)
+	require.Equal(t, 2, got.Usage.InputTokens)
+	require.Equal(t, 3, got.Usage.OutputTokens)
+	require.Equal(t, "", got.RequestModel)
+}
+
+func TestIsDisconnectErrorCoverage_CloseStatusesAndMessageBranches(t *testing.T) {
+	t.Parallel()
+
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusNormalClosure}))
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusNoStatusRcvd}))
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusAbnormalClosure}))
+	require.True(t, isDisconnectError(errors.New("connection reset by peer")))
+	require.False(t, isDisconnectError(errors.New("   ")))
+}
+
+func TestIsTokenEventCoverageBranches(t *testing.T) {
+	t.Parallel()
+
+	require.False(t, isTokenEvent("response.in_progress"))
+	require.False(t, isTokenEvent("response.output_item.added"))
+	require.True(t, isTokenEvent("response.output_audio.delta"))
+	require.True(t, isTokenEvent("response.output"))
+	require.True(t, isTokenEvent("response.done"))
+}
+
+func TestRelayTurnTimingHelpersCoverage(t *testing.T) {
+	t.Parallel()
+
+	now := time.Unix(100, 0)
+	// nil state
+	require.Nil(t, openAIWSRelayGetOrInitTurnTiming(nil, "resp_nil", now))
+	_, ok := openAIWSRelayDeleteTurnTiming(nil, "resp_nil")
+	require.False(t, ok)
+
+	state := &relayState{}
+	timing := openAIWSRelayGetOrInitTurnTiming(state, "resp_a", now)
+	require.NotNil(t, timing)
+	require.Equal(t, now, timing.startAt)
+
+	// 再次获取返回同一条 timing
+	timing2 := openAIWSRelayGetOrInitTurnTiming(state, "resp_a", now.Add(5*time.Second))
+	require.NotNil(t, timing2)
+	require.Equal(t, now, timing2.startAt)
+
+	// 删除存在键
+	deleted, ok := openAIWSRelayDeleteTurnTiming(state, "resp_a")
+	require.True(t, ok)
+	require.Equal(t, now, deleted.startAt)
+
+	// 删除不存在键
+	_, ok = openAIWSRelayDeleteTurnTiming(state, "resp_a")
+	require.False(t, ok)
+}
+
+func TestObserveUpstreamMessage_ResponseIDFallbackPolicy(t *testing.T) {
+	t.Parallel()
+
+	state := &relayState{requestModel: "gpt-5"}
+	startAt := time.Unix(0, 0)
+	now := startAt
+	nowFn := func() time.Time {
+		now = now.Add(5 * time.Millisecond)
+		return now
+	}
+
+	// 非 terminal：仅有顶层 id，不应把 event id 当成 response_id。
+	observed := observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.output_text.delta","id":"evt_123","delta":"hi"}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	require.False(t, observed.terminal)
+	require.Equal(t, "", observed.responseID)
+
+	// terminal：允许兜底用顶层 id（用于兼容少数字段变体）。
+	observed = observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.completed","id":"resp_fallback","response":{"usage":{"input_tokens":1,"output_tokens":1}}}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	require.True(t, observed.terminal)
+	require.Equal(t, "resp_fallback", observed.responseID)
+}
--- a/backend/internal/service/openai_ws_v2/passthrough_relay_test.go
+++ b/backend/internal/service/openai_ws_v2/passthrough_relay_test.go
@@ -0,0 +1,752 @@
+package openai_ws_v2
+
+import (
+	"context"
+	"errors"
+	"io"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	coderws "github.com/coder/websocket"
+	"github.com/stretchr/testify/require"
+)
+
+type passthroughTestFrame struct {
+	msgType coderws.MessageType
+	payload []byte
+}
+
+type passthroughTestFrameConn struct {
+	mu     sync.Mutex
+	writes []passthroughTestFrame
+	readCh chan passthroughTestFrame
+	once   sync.Once
+}
+
+type delayedReadFrameConn struct {
+	base       FrameConn
+	firstDelay time.Duration
+	once       sync.Once
+}
+
+type closeSpyFrameConn struct {
+	closeCalls atomic.Int32
+}
+
+func newPassthroughTestFrameConn(frames []passthroughTestFrame, autoClose bool) *passthroughTestFrameConn {
+	c := &passthroughTestFrameConn{
+		readCh: make(chan passthroughTestFrame, len(frames)+1),
+	}
+	for _, frame := range frames {
+		copied := passthroughTestFrame{msgType: frame.msgType, payload: append([]byte(nil), frame.payload...)}
+		c.readCh <- copied
+	}
+	if autoClose {
+		close(c.readCh)
+	}
+	return c
+}
+
+func (c *passthroughTestFrameConn) ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error) {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	select {
+	case <-ctx.Done():
+		return coderws.MessageText, nil, ctx.Err()
+	case frame, ok := <-c.readCh:
+		if !ok {
+			return coderws.MessageText, nil, io.EOF
+		}
+		return frame.msgType, append([]byte(nil), frame.payload...), nil
+	}
+}
+
+func (c *passthroughTestFrameConn) WriteFrame(ctx context.Context, msgType coderws.MessageType, payload []byte) error {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.writes = append(c.writes, passthroughTestFrame{msgType: msgType, payload: append([]byte(nil), payload...)})
+	return nil
+}
+
+func (c *passthroughTestFrameConn) Close() error {
+	c.once.Do(func() {
+		defer func() { _ = recover() }()
+		close(c.readCh)
+	})
+	return nil
+}
+
+func (c *passthroughTestFrameConn) Writes() []passthroughTestFrame {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	out := make([]passthroughTestFrame, len(c.writes))
+	copy(out, c.writes)
+	return out
+}
+
+func (c *delayedReadFrameConn) ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error) {
+	if c == nil || c.base == nil {
+		return coderws.MessageText, nil, io.EOF
+	}
+	c.once.Do(func() {
+		if c.firstDelay > 0 {
+			timer := time.NewTimer(c.firstDelay)
+			defer timer.Stop()
+			select {
+			case <-ctx.Done():
+			case <-timer.C:
+			}
+		}
+	})
+	return c.base.ReadFrame(ctx)
+}
+
+func (c *delayedReadFrameConn) WriteFrame(ctx context.Context, msgType coderws.MessageType, payload []byte) error {
+	if c == nil || c.base == nil {
+		return io.EOF
+	}
+	return c.base.WriteFrame(ctx, msgType, payload)
+}
+
+func (c *delayedReadFrameConn) Close() error {
+	if c == nil || c.base == nil {
+		return nil
+	}
+	return c.base.Close()
+}
+
+func (c *closeSpyFrameConn) ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error) {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	<-ctx.Done()
+	return coderws.MessageText, nil, ctx.Err()
+}
+
+func (c *closeSpyFrameConn) WriteFrame(ctx context.Context, _ coderws.MessageType, _ []byte) error {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+		return nil
+	}
+}
+
+func (c *closeSpyFrameConn) Close() error {
+	if c != nil {
+		c.closeCalls.Add(1)
+	}
+	return nil
+}
+
+func (c *closeSpyFrameConn) CloseCalls() int32 {
+	if c == nil {
+		return 0
+	}
+	return c.closeCalls.Load()
+}
+
+func TestRelay_BasicRelayAndUsage(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_123","usage":{"input_tokens":7,"output_tokens":3,"input_tokens_details":{"cached_tokens":2}}}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-5.3-codex","input":[{"type":"input_text","text":"hello"}]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.Nil(t, relayExit)
+	require.Equal(t, "gpt-5.3-codex", result.RequestModel)
+	require.Equal(t, "resp_123", result.RequestID)
+	require.Equal(t, "response.completed", result.TerminalEventType)
+	require.Equal(t, 7, result.Usage.InputTokens)
+	require.Equal(t, 3, result.Usage.OutputTokens)
+	require.Equal(t, 2, result.Usage.CacheReadInputTokens)
+	require.NotNil(t, result.FirstTokenMs)
+	require.Equal(t, int64(1), result.ClientToUpstreamFrames)
+	require.Equal(t, int64(1), result.UpstreamToClientFrames)
+	require.Equal(t, int64(0), result.DroppedDownstreamFrames)
+
+	upstreamWrites := upstreamConn.Writes()
+	require.Len(t, upstreamWrites, 1)
+	require.Equal(t, coderws.MessageText, upstreamWrites[0].msgType)
+	require.JSONEq(t, string(firstPayload), string(upstreamWrites[0].payload))
+
+	clientWrites := clientConn.Writes()
+	require.Len(t, clientWrites, 1)
+	require.Equal(t, coderws.MessageText, clientWrites[0].msgType)
+	require.JSONEq(t, `{"type":"response.completed","response":{"id":"resp_123","usage":{"input_tokens":7,"output_tokens":3,"input_tokens_details":{"cached_tokens":2}}}}`, string(clientWrites[0].payload))
+}
+
+func TestRelay_FunctionCallOutputBytesPreserved(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_func","usage":{"input_tokens":1,"output_tokens":1}}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-5.3-codex","input":[{"type":"function_call_output","call_id":"call_abc123","output":"{\"ok\":true}"}]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	_, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.Nil(t, relayExit)
+
+	upstreamWrites := upstreamConn.Writes()
+	require.Len(t, upstreamWrites, 1)
+	require.Equal(t, coderws.MessageText, upstreamWrites[0].msgType)
+	require.Equal(t, firstPayload, upstreamWrites[0].payload)
+}
+
+func TestRelay_UpstreamDisconnect(t *testing.T) {
+	t.Parallel()
+
+	// 上游立即关闭（EOF），客户端不发送额外帧
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn(nil, true) // 立即 close -> EOF
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	// 上游 EOF 属于 disconnect，标记为 graceful
+	require.Nil(t, relayExit, "上游 EOF 应被视为 graceful disconnect")
+	require.Equal(t, "gpt-4o", result.RequestModel)
+}
+
+func TestRelay_ClientDisconnect(t *testing.T) {
+	t.Parallel()
+
+	// 客户端立即关闭（EOF），上游阻塞读取直到 context 取消
+	clientConn := newPassthroughTestFrameConn(nil, true) // 立即 close -> EOF
+	upstreamConn := newPassthroughTestFrameConn(nil, false)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.NotNil(t, relayExit, "客户端 EOF 应返回可观测的中断状态")
+	require.Equal(t, "client_disconnected", relayExit.Stage)
+	require.Equal(t, "gpt-4o", result.RequestModel)
+}
+
+func TestRelay_ClientDisconnect_DrainCapturesLateUsage(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, true)
+	upstreamBase := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_drain","usage":{"input_tokens":6,"output_tokens":4,"input_tokens_details":{"cached_tokens":1}}}}`),
+		},
+	}, true)
+	upstreamConn := &delayedReadFrameConn{
+		base:       upstreamBase,
+		firstDelay: 80 * time.Millisecond,
+	}
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		UpstreamDrainTimeout: 400 * time.Millisecond,
+	})
+	require.NotNil(t, relayExit)
+	require.Equal(t, "client_disconnected", relayExit.Stage)
+	require.Equal(t, "resp_drain", result.RequestID)
+	require.Equal(t, "response.completed", result.TerminalEventType)
+	require.Equal(t, 6, result.Usage.InputTokens)
+	require.Equal(t, 4, result.Usage.OutputTokens)
+	require.Equal(t, 1, result.Usage.CacheReadInputTokens)
+	require.Equal(t, int64(1), result.ClientToUpstreamFrames)
+	require.Equal(t, int64(0), result.UpstreamToClientFrames)
+	require.Equal(t, int64(1), result.DroppedDownstreamFrames)
+}
+
+func TestRelay_IdleTimeout(t *testing.T) {
+	t.Parallel()
+
+	// 客户端和上游都不发送帧，idle timeout 应触发
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn(nil, false)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	// 使用快进时间来加速 idle timeout
+	now := time.Now()
+	callCount := 0
+	nowFn := func() time.Time {
+		callCount++
+		// 前几次调用返回正常时间（初始化阶段），之后快进
+		if callCount <= 5 {
+			return now
+		}
+		return now.Add(time.Hour) // 快进到超时
+	}
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		IdleTimeout: 2 * time.Second,
+		Now:         nowFn,
+	})
+	require.NotNil(t, relayExit, "应因 idle timeout 退出")
+	require.Equal(t, "idle_timeout", relayExit.Stage)
+	require.Equal(t, "gpt-4o", result.RequestModel)
+}
+
+func TestRelay_IdleTimeoutDoesNotCloseClientOnError(t *testing.T) {
+	t.Parallel()
+
+	clientConn := &closeSpyFrameConn{}
+	upstreamConn := &closeSpyFrameConn{}
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	now := time.Now()
+	callCount := 0
+	nowFn := func() time.Time {
+		callCount++
+		if callCount <= 5 {
+			return now
+		}
+		return now.Add(time.Hour)
+	}
+
+	_, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		IdleTimeout: 2 * time.Second,
+		Now:         nowFn,
+	})
+	require.NotNil(t, relayExit, "应因 idle timeout 退出")
+	require.Equal(t, "idle_timeout", relayExit.Stage)
+	require.Zero(t, clientConn.CloseCalls(), "错误路径不应提前关闭客户端连接，交给上层决定 close code")
+	require.GreaterOrEqual(t, upstreamConn.CloseCalls(), int32(1))
+}
+
+func TestRelay_NilConnections(t *testing.T) {
+	t.Parallel()
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx := context.Background()
+
+	t.Run("nil client conn", func(t *testing.T) {
+		upstreamConn := newPassthroughTestFrameConn(nil, true)
+		_, relayExit := Relay(ctx, nil, upstreamConn, firstPayload, RelayOptions{})
+		require.NotNil(t, relayExit)
+		require.Equal(t, "relay_init", relayExit.Stage)
+		require.Contains(t, relayExit.Err.Error(), "nil")
+	})
+
+	t.Run("nil upstream conn", func(t *testing.T) {
+		clientConn := newPassthroughTestFrameConn(nil, true)
+		_, relayExit := Relay(ctx, clientConn, nil, firstPayload, RelayOptions{})
+		require.NotNil(t, relayExit)
+		require.Equal(t, "relay_init", relayExit.Stage)
+		require.Contains(t, relayExit.Err.Error(), "nil")
+	})
+}
+
+func TestRelay_MultipleUpstreamMessages(t *testing.T) {
+	t.Parallel()
+
+	// 上游发送多个事件（delta + completed），验证多帧中继和 usage 聚合
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.output_text.delta","delta":"Hello"}`),
+		},
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.output_text.delta","delta":" world"}`),
+		},
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_multi","usage":{"input_tokens":10,"output_tokens":5,"input_tokens_details":{"cached_tokens":3}}}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[{"type":"input_text","text":"hi"}]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.Nil(t, relayExit)
+	require.Equal(t, "resp_multi", result.RequestID)
+	require.Equal(t, "response.completed", result.TerminalEventType)
+	require.Equal(t, 10, result.Usage.InputTokens)
+	require.Equal(t, 5, result.Usage.OutputTokens)
+	require.Equal(t, 3, result.Usage.CacheReadInputTokens)
+	require.NotNil(t, result.FirstTokenMs)
+
+	// 验证所有 3 个上游帧都转发给了客户端
+	clientWrites := clientConn.Writes()
+	require.Len(t, clientWrites, 3)
+}
+
+func TestRelay_OnTurnComplete_PerTerminalEvent(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_turn_1","usage":{"input_tokens":2,"output_tokens":1}}}`),
+		},
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.failed","response":{"id":"resp_turn_2","usage":{"input_tokens":3,"output_tokens":4}}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-5.3-codex","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	turns := make([]RelayTurnResult, 0, 2)
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		OnTurnComplete: func(turn RelayTurnResult) {
+			turns = append(turns, turn)
+		},
+	})
+	require.Nil(t, relayExit)
+	require.Len(t, turns, 2)
+	require.Equal(t, "resp_turn_1", turns[0].RequestID)
+	require.Equal(t, "response.completed", turns[0].TerminalEventType)
+	require.Equal(t, 2, turns[0].Usage.InputTokens)
+	require.Equal(t, 1, turns[0].Usage.OutputTokens)
+	require.Equal(t, "resp_turn_2", turns[1].RequestID)
+	require.Equal(t, "response.failed", turns[1].TerminalEventType)
+	require.Equal(t, 3, turns[1].Usage.InputTokens)
+	require.Equal(t, 4, turns[1].Usage.OutputTokens)
+	require.Equal(t, 5, result.Usage.InputTokens)
+	require.Equal(t, 5, result.Usage.OutputTokens)
+}
+
+func TestRelay_OnTurnComplete_ProvidesTurnMetrics(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.output_text.delta","response_id":"resp_metric","delta":"hi"}`),
+		},
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_metric","usage":{"input_tokens":2,"output_tokens":1}}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-5.3-codex","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	base := time.Unix(0, 0)
+	var nowTick atomic.Int64
+	nowFn := func() time.Time {
+		step := nowTick.Add(1)
+		return base.Add(time.Duration(step) * 5 * time.Millisecond)
+	}
+
+	var turn RelayTurnResult
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		Now: nowFn,
+		OnTurnComplete: func(current RelayTurnResult) {
+			turn = current
+		},
+	})
+	require.Nil(t, relayExit)
+	require.Equal(t, "resp_metric", turn.RequestID)
+	require.Equal(t, "response.completed", turn.TerminalEventType)
+	require.NotNil(t, turn.FirstTokenMs)
+	require.GreaterOrEqual(t, *turn.FirstTokenMs, 0)
+	require.Greater(t, turn.Duration.Milliseconds(), int64(0))
+	require.NotNil(t, result.FirstTokenMs)
+	require.Greater(t, result.Duration.Milliseconds(), int64(0))
+}
+
+func TestRelay_BinaryFramePassthrough(t *testing.T) {
+	t.Parallel()
+
+	// 验证 binary frame 被透传但不进行 usage 解析
+	binaryPayload := []byte{0x00, 0x01, 0x02, 0x03}
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageBinary,
+			payload: binaryPayload,
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.Nil(t, relayExit)
+	// binary frame 不解析 usage
+	require.Equal(t, 0, result.Usage.InputTokens)
+
+	clientWrites := clientConn.Writes()
+	require.Len(t, clientWrites, 1)
+	require.Equal(t, coderws.MessageBinary, clientWrites[0].msgType)
+	require.Equal(t, binaryPayload, clientWrites[0].payload)
+}
+
+func TestRelay_BinaryJSONFrameSkipsObservation(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageBinary,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_binary","usage":{"input_tokens":7,"output_tokens":3}}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.Nil(t, relayExit)
+	require.Equal(t, 0, result.Usage.InputTokens)
+	require.Equal(t, "", result.RequestID)
+	require.Equal(t, "", result.TerminalEventType)
+
+	clientWrites := clientConn.Writes()
+	require.Len(t, clientWrites, 1)
+	require.Equal(t, coderws.MessageBinary, clientWrites[0].msgType)
+}
+
+func TestRelay_UpstreamErrorEventPassthroughRaw(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	errorEvent := []byte(`{"type":"error","error":{"type":"invalid_request_error","message":"No tool call found"}}`)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: errorEvent,
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	_, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.Nil(t, relayExit)
+
+	clientWrites := clientConn.Writes()
+	require.Len(t, clientWrites, 1)
+	require.Equal(t, coderws.MessageText, clientWrites[0].msgType)
+	require.Equal(t, errorEvent, clientWrites[0].payload)
+}
+
+func TestRelay_PreservesFirstMessageType(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn(nil, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	_, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		FirstMessageType: coderws.MessageBinary,
+	})
+	require.Nil(t, relayExit)
+
+	upstreamWrites := upstreamConn.Writes()
+	require.Len(t, upstreamWrites, 1)
+	require.Equal(t, coderws.MessageBinary, upstreamWrites[0].msgType)
+	require.Equal(t, firstPayload, upstreamWrites[0].payload)
+}
+
+func TestRelay_UsageParseFailureDoesNotBlockRelay(t *testing.T) {
+	baseline := SnapshotMetrics().UsageParseFailureTotal
+
+	// 上游发送无效 JSON（非 usage 格式），不应影响透传
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_bad","usage":"not_an_object"}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	result, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	require.Nil(t, relayExit)
+	// usage 解析失败，值为 0 但不影响透传
+	require.Equal(t, 0, result.Usage.InputTokens)
+	require.Equal(t, "response.completed", result.TerminalEventType)
+
+	// 帧仍然被转发
+	clientWrites := clientConn.Writes()
+	require.Len(t, clientWrites, 1)
+	require.GreaterOrEqual(t, SnapshotMetrics().UsageParseFailureTotal, baseline+1)
+}
+
+func TestRelay_WriteUpstreamFirstMessageFails(t *testing.T) {
+	t.Parallel()
+
+	// 上游连接立即关闭，首包写入失败
+	upstreamConn := newPassthroughTestFrameConn(nil, true)
+	_ = upstreamConn.Close()
+
+	// 覆盖 WriteFrame 使其返回错误
+	errConn := &errorOnWriteFrameConn{}
+	clientConn := newPassthroughTestFrameConn(nil, false)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	_, relayExit := Relay(ctx, clientConn, errConn, firstPayload, RelayOptions{})
+	require.NotNil(t, relayExit)
+	require.Equal(t, "write_upstream", relayExit.Stage)
+}
+
+func TestRelay_ContextCanceled(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn(nil, false)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+
+	// 立即取消 context
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	_, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{})
+	// context 取消导致写首包失败
+	require.NotNil(t, relayExit)
+}
+
+func TestRelay_TraceEvents_ContainsLifecycleStages(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_trace","usage":{"input_tokens":1,"output_tokens":1}}}`),
+		},
+	}, true)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	stages := make([]string, 0, 8)
+	var stagesMu sync.Mutex
+	_, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		OnTrace: func(event RelayTraceEvent) {
+			stagesMu.Lock()
+			stages = append(stages, event.Stage)
+			stagesMu.Unlock()
+		},
+	})
+	require.Nil(t, relayExit)
+	stagesMu.Lock()
+	capturedStages := append([]string(nil), stages...)
+	stagesMu.Unlock()
+	require.Contains(t, capturedStages, "relay_start")
+	require.Contains(t, capturedStages, "write_first_message_ok")
+	require.Contains(t, capturedStages, "first_exit")
+	require.Contains(t, capturedStages, "relay_complete")
+}
+
+func TestRelay_TraceEvents_IdleTimeout(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn(nil, false)
+
+	firstPayload := []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	now := time.Now()
+	callCount := 0
+	nowFn := func() time.Time {
+		callCount++
+		if callCount <= 5 {
+			return now
+		}
+		return now.Add(time.Hour)
+	}
+
+	stages := make([]string, 0, 8)
+	var stagesMu sync.Mutex
+	_, relayExit := Relay(ctx, clientConn, upstreamConn, firstPayload, RelayOptions{
+		IdleTimeout: 2 * time.Second,
+		Now:         nowFn,
+		OnTrace: func(event RelayTraceEvent) {
+			stagesMu.Lock()
+			stages = append(stages, event.Stage)
+			stagesMu.Unlock()
+		},
+	})
+	require.NotNil(t, relayExit)
+	require.Equal(t, "idle_timeout", relayExit.Stage)
+	stagesMu.Lock()
+	capturedStages := append([]string(nil), stages...)
+	stagesMu.Unlock()
+	require.Contains(t, capturedStages, "idle_timeout_triggered")
+	require.Contains(t, capturedStages, "relay_exit")
+}
+
+// errorOnWriteFrameConn 是一个写入总是失败的 FrameConn 实现，用于测试首包写入失败。
+type errorOnWriteFrameConn struct{}
+
+func (c *errorOnWriteFrameConn) ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error) {
+	<-ctx.Done()
+	return coderws.MessageText, nil, ctx.Err()
+}
+
+func (c *errorOnWriteFrameConn) WriteFrame(_ context.Context, _ coderws.MessageType, _ []byte) error {
+	return errors.New("write failed: connection refused")
+}
+
+func (c *errorOnWriteFrameConn) Close() error {
+	return nil
+}
--- a/backend/internal/service/openai_ws_v2_passthrough_adapter.go
+++ b/backend/internal/service/openai_ws_v2_passthrough_adapter.go
@@ -0,0 +1,367 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync/atomic"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/logger"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/openai"
+	openaiwsv2 "github.com/Wei-Shaw/sub2api/internal/service/openai_ws_v2"
+	coderws "github.com/coder/websocket"
+	"github.com/gin-gonic/gin"
+	"github.com/tidwall/gjson"
+)
+
+type openAIWSClientFrameConn struct {
+	conn *coderws.Conn
+}
+
+const openaiWSV2PassthroughModeFields = "ws_mode=passthrough ws_router=v2"
+
+var _ openaiwsv2.FrameConn = (*openAIWSClientFrameConn)(nil)
+
+func (c *openAIWSClientFrameConn) ReadFrame(ctx context.Context) (coderws.MessageType, []byte, error) {
+	if c == nil || c.conn == nil {
+		return coderws.MessageText, nil, errOpenAIWSConnClosed
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	return c.conn.Read(ctx)
+}
+
+func (c *openAIWSClientFrameConn) WriteFrame(ctx context.Context, msgType coderws.MessageType, payload []byte) error {
+	if c == nil || c.conn == nil {
+		return errOpenAIWSConnClosed
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	return c.conn.Write(ctx, msgType, payload)
+}
+
+func (c *openAIWSClientFrameConn) Close() error {
+	if c == nil || c.conn == nil {
+		return nil
+	}
+	_ = c.conn.Close(coderws.StatusNormalClosure, "")
+	_ = c.conn.CloseNow()
+	return nil
+}
+
+func (s *OpenAIGatewayService) proxyResponsesWebSocketV2Passthrough(
+	ctx context.Context,
+	c *gin.Context,
+	clientConn *coderws.Conn,
+	account *Account,
+	token string,
+	firstClientMessage []byte,
+	hooks *OpenAIWSIngressHooks,
+	wsDecision OpenAIWSProtocolDecision,
+) error {
+	if s == nil {
+		return errors.New("service is nil")
+	}
+	if clientConn == nil {
+		return errors.New("client websocket is nil")
+	}
+	if account == nil {
+		return errors.New("account is nil")
+	}
+	if strings.TrimSpace(token) == "" {
+		return errors.New("token is empty")
+	}
+	requestModel := strings.TrimSpace(gjson.GetBytes(firstClientMessage, "model").String())
+	requestPreviousResponseID := strings.TrimSpace(gjson.GetBytes(firstClientMessage, "previous_response_id").String())
+	logOpenAIWSV2Passthrough(
+		"relay_start account_id=%d model=%s previous_response_id=%s first_message_type=%s first_message_bytes=%d",
+		account.ID,
+		truncateOpenAIWSLogValue(requestModel, openAIWSLogValueMaxLen),
+		truncateOpenAIWSLogValue(requestPreviousResponseID, openAIWSIDValueMaxLen),
+		openaiwsv2RelayMessageTypeName(coderws.MessageText),
+		len(firstClientMessage),
+	)
+
+	wsURL, err := s.buildOpenAIResponsesWSURL(account)
+	if err != nil {
+		return fmt.Errorf("build ws url: %w", err)
+	}
+	wsHost := "-"
+	wsPath := "-"
+	if parsedURL, parseErr := url.Parse(wsURL); parseErr == nil && parsedURL != nil {
+		wsHost = normalizeOpenAIWSLogValue(parsedURL.Host)
+		wsPath = normalizeOpenAIWSLogValue(parsedURL.Path)
+	}
+	logOpenAIWSV2Passthrough(
+		"relay_dial_start account_id=%d ws_host=%s ws_path=%s proxy_enabled=%v",
+		account.ID,
+		wsHost,
+		wsPath,
+		account.ProxyID != nil && account.Proxy != nil,
+	)
+
+	isCodexCLI := false
+	if c != nil {
+		isCodexCLI = openai.IsCodexCLIRequest(c.GetHeader("User-Agent"))
+	}
+	if s.cfg != nil && s.cfg.Gateway.ForceCodexCLI {
+		isCodexCLI = true
+	}
+	headers, _ := s.buildOpenAIWSHeaders(c, account, token, wsDecision, isCodexCLI, "", "", "")
+	proxyURL := ""
+	if account.ProxyID != nil && account.Proxy != nil {
+		proxyURL = account.Proxy.URL()
+	}
+
+	dialer := s.getOpenAIWSPassthroughDialer()
+	if dialer == nil {
+		return errors.New("openai ws passthrough dialer is nil")
+	}
+
+	dialCtx, cancelDial := context.WithTimeout(ctx, s.openAIWSDialTimeout())
+	defer cancelDial()
+	upstreamConn, statusCode, handshakeHeaders, err := dialer.Dial(dialCtx, wsURL, headers, proxyURL)
+	if err != nil {
+		logOpenAIWSV2Passthrough(
+			"relay_dial_failed account_id=%d status_code=%d err=%s",
+			account.ID,
+			statusCode,
+			truncateOpenAIWSLogValue(err.Error(), openAIWSLogValueMaxLen),
+		)
+		return s.mapOpenAIWSPassthroughDialError(err, statusCode, handshakeHeaders)
+	}
+	defer func() {
+		_ = upstreamConn.Close()
+	}()
+	logOpenAIWSV2Passthrough(
+		"relay_dial_ok account_id=%d status_code=%d upstream_request_id=%s",
+		account.ID,
+		statusCode,
+		openAIWSHeaderValueForLog(handshakeHeaders, "x-request-id"),
+	)
+
+	upstreamFrameConn, ok := upstreamConn.(openaiwsv2.FrameConn)
+	if !ok {
+		return errors.New("openai ws passthrough upstream connection does not support frame relay")
+	}
+
+	completedTurns := atomic.Int32{}
+	relayResult, relayExit := openaiwsv2.RunEntry(openaiwsv2.EntryInput{
+		Ctx:                ctx,
+		ClientConn:         &openAIWSClientFrameConn{conn: clientConn},
+		UpstreamConn:       upstreamFrameConn,
+		FirstClientMessage: firstClientMessage,
+		Options: openaiwsv2.RelayOptions{
+			WriteTimeout:     s.openAIWSWriteTimeout(),
+			IdleTimeout:      s.openAIWSPassthroughIdleTimeout(),
+			FirstMessageType: coderws.MessageText,
+			OnUsageParseFailure: func(eventType string, usageRaw string) {
+				logOpenAIWSV2Passthrough(
+					"usage_parse_failed event_type=%s usage_raw=%s",
+					truncateOpenAIWSLogValue(eventType, openAIWSLogValueMaxLen),
+					truncateOpenAIWSLogValue(usageRaw, openAIWSLogValueMaxLen),
+				)
+			},
+			OnTurnComplete: func(turn openaiwsv2.RelayTurnResult) {
+				turnNo := int(completedTurns.Add(1))
+				turnResult := &OpenAIForwardResult{
+					RequestID: turn.RequestID,
+					Usage: OpenAIUsage{
+						InputTokens:              turn.Usage.InputTokens,
+						OutputTokens:             turn.Usage.OutputTokens,
+						CacheCreationInputTokens: turn.Usage.CacheCreationInputTokens,
+						CacheReadInputTokens:     turn.Usage.CacheReadInputTokens,
+					},
+					Model:        turn.RequestModel,
+					Stream:       true,
+					OpenAIWSMode: true,
+					Duration:     turn.Duration,
+					FirstTokenMs: turn.FirstTokenMs,
+				}
+				logOpenAIWSV2Passthrough(
+					"relay_turn_completed account_id=%d turn=%d request_id=%s terminal_event=%s duration_ms=%d first_token_ms=%d input_tokens=%d output_tokens=%d cache_read_tokens=%d",
+					account.ID,
+					turnNo,
+					truncateOpenAIWSLogValue(turnResult.RequestID, openAIWSIDValueMaxLen),
+					truncateOpenAIWSLogValue(turn.TerminalEventType, openAIWSLogValueMaxLen),
+					turnResult.Duration.Milliseconds(),
+					openAIWSFirstTokenMsForLog(turnResult.FirstTokenMs),
+					turnResult.Usage.InputTokens,
+					turnResult.Usage.OutputTokens,
+					turnResult.Usage.CacheReadInputTokens,
+				)
+				if hooks != nil && hooks.AfterTurn != nil {
+					hooks.AfterTurn(turnNo, turnResult, nil)
+				}
+			},
+			OnTrace: func(event openaiwsv2.RelayTraceEvent) {
+				logOpenAIWSV2Passthrough(
+					"relay_trace account_id=%d stage=%s direction=%s msg_type=%s bytes=%d graceful=%v wrote_downstream=%v err=%s",
+					account.ID,
+					truncateOpenAIWSLogValue(event.Stage, openAIWSLogValueMaxLen),
+					truncateOpenAIWSLogValue(event.Direction, openAIWSLogValueMaxLen),
+					truncateOpenAIWSLogValue(event.MessageType, openAIWSLogValueMaxLen),
+					event.PayloadBytes,
+					event.Graceful,
+					event.WroteDownstream,
+					truncateOpenAIWSLogValue(event.Error, openAIWSLogValueMaxLen),
+				)
+			},
+		},
+	})
+
+	result := &OpenAIForwardResult{
+		RequestID: relayResult.RequestID,
+		Usage: OpenAIUsage{
+			InputTokens:              relayResult.Usage.InputTokens,
+			OutputTokens:             relayResult.Usage.OutputTokens,
+			CacheCreationInputTokens: relayResult.Usage.CacheCreationInputTokens,
+			CacheReadInputTokens:     relayResult.Usage.CacheReadInputTokens,
+		},
+		Model:        relayResult.RequestModel,
+		Stream:       true,
+		OpenAIWSMode: true,
+		Duration:     relayResult.Duration,
+		FirstTokenMs: relayResult.FirstTokenMs,
+	}
+
+	turnCount := int(completedTurns.Load())
+	if relayExit == nil {
+		logOpenAIWSV2Passthrough(
+			"relay_completed account_id=%d request_id=%s terminal_event=%s duration_ms=%d c2u_frames=%d u2c_frames=%d dropped_frames=%d turns=%d",
+			account.ID,
+			truncateOpenAIWSLogValue(result.RequestID, openAIWSIDValueMaxLen),
+			truncateOpenAIWSLogValue(relayResult.TerminalEventType, openAIWSLogValueMaxLen),
+			result.Duration.Milliseconds(),
+			relayResult.ClientToUpstreamFrames,
+			relayResult.UpstreamToClientFrames,
+			relayResult.DroppedDownstreamFrames,
+			turnCount,
+		)
+		// 正常路径按 terminal 事件逐 turn 已回调；仅在零 turn 场景兜底回调一次。
+		if turnCount == 0 && hooks != nil && hooks.AfterTurn != nil {
+			hooks.AfterTurn(1, result, nil)
+		}
+		return nil
+	}
+	logOpenAIWSV2Passthrough(
+		"relay_failed account_id=%d stage=%s wrote_downstream=%v err=%s duration_ms=%d c2u_frames=%d u2c_frames=%d dropped_frames=%d turns=%d",
+		account.ID,
+		truncateOpenAIWSLogValue(relayExit.Stage, openAIWSLogValueMaxLen),
+		relayExit.WroteDownstream,
+		truncateOpenAIWSLogValue(relayErrorText(relayExit.Err), openAIWSLogValueMaxLen),
+		result.Duration.Milliseconds(),
+		relayResult.ClientToUpstreamFrames,
+		relayResult.UpstreamToClientFrames,
+		relayResult.DroppedDownstreamFrames,
+		turnCount,
+	)
+
+	relayErr := relayExit.Err
+	if relayExit.Stage == "idle_timeout" {
+		relayErr = NewOpenAIWSClientCloseError(
+			coderws.StatusPolicyViolation,
+			"client websocket idle timeout",
+			relayErr,
+		)
+	}
+	turnErr := wrapOpenAIWSIngressTurnError(
+		relayExit.Stage,
+		relayErr,
+		relayExit.WroteDownstream,
+	)
+	if hooks != nil && hooks.AfterTurn != nil {
+		hooks.AfterTurn(turnCount+1, nil, turnErr)
+	}
+	return turnErr
+}
+
+func (s *OpenAIGatewayService) mapOpenAIWSPassthroughDialError(
+	err error,
+	statusCode int,
+	handshakeHeaders http.Header,
+) error {
+	if err == nil {
+		return nil
+	}
+	wrappedErr := err
+	var dialErr *openAIWSDialError
+	if !errors.As(err, &dialErr) {
+		wrappedErr = &openAIWSDialError{
+			StatusCode:      statusCode,
+			ResponseHeaders: cloneHeader(handshakeHeaders),
+			Err:             err,
+		}
+	}
+
+	if errors.Is(err, context.Canceled) {
+		return err
+	}
+	if errors.Is(err, context.DeadlineExceeded) {
+		return NewOpenAIWSClientCloseError(
+			coderws.StatusTryAgainLater,
+			"upstream websocket connect timeout",
+			wrappedErr,
+		)
+	}
+	if statusCode == http.StatusTooManyRequests {
+		return NewOpenAIWSClientCloseError(
+			coderws.StatusTryAgainLater,
+			"upstream websocket is busy, please retry later",
+			wrappedErr,
+		)
+	}
+	if statusCode == http.StatusUnauthorized || statusCode == http.StatusForbidden {
+		return NewOpenAIWSClientCloseError(
+			coderws.StatusPolicyViolation,
+			"upstream websocket authentication failed",
+			wrappedErr,
+		)
+	}
+	if statusCode >= http.StatusBadRequest && statusCode < http.StatusInternalServerError {
+		return NewOpenAIWSClientCloseError(
+			coderws.StatusPolicyViolation,
+			"upstream websocket handshake rejected",
+			wrappedErr,
+		)
+	}
+	return fmt.Errorf("openai ws passthrough dial: %w", wrappedErr)
+}
+
+func openaiwsv2RelayMessageTypeName(msgType coderws.MessageType) string {
+	switch msgType {
+	case coderws.MessageText:
+		return "text"
+	case coderws.MessageBinary:
+		return "binary"
+	default:
+		return fmt.Sprintf("unknown(%d)", msgType)
+	}
+}
+
+func relayErrorText(err error) string {
+	if err == nil {
+		return ""
+	}
+	return err.Error()
+}
+
+func openAIWSFirstTokenMsForLog(firstTokenMs *int) int {
+	if firstTokenMs == nil {
+		return -1
+	}
+	return *firstTokenMs
+}
+
+func logOpenAIWSV2Passthrough(format string, args ...any) {
+	logger.LegacyPrintf(
+		"service.openai_ws_v2",
+		"[OpenAI WS v2 passthrough] %s "+format,
+		append([]any{openaiWSV2PassthroughModeFields}, args...)...,
+	)
+}