diff --git a/backend/internal/handler/gateway_handler.go b/backend/internal/handler/gateway_handler.go
index 970d7472..be55e69b 100644
--- a/backend/internal/handler/gateway_handler.go
+++ b/backend/internal/handler/gateway_handler.go
@@ -1423,7 +1423,7 @@ func (h *GatewayHandler) handleStreamingAwareError(c *gin.Context, status int, e
 		// /v1/responses 的严格 SDK（Codex CLI）要求终止事件必须属于
 		// response.completed/failed/incomplete/cancelled 集合。
 		// Anthropic-backed Responses 路径同样会因为通用 error 帧被拒。
-		if GetInboundEndpoint(c) == EndpointResponses {
+		if inboundIsResponses(c) {
 			if writeResponsesFailedSSE(c, errType, message) {
 				return
 			}
diff --git a/backend/internal/handler/openai_gateway_handler.go b/backend/internal/handler/openai_gateway_handler.go
index dd00a244..ea95b812 100644
--- a/backend/internal/handler/openai_gateway_handler.go
+++ b/backend/internal/handler/openai_gateway_handler.go
@@ -1695,7 +1695,7 @@ func (h *OpenAIGatewayHandler) handleStreamingAwareError(c *gin.Context, status
 		// response.completed/failed/incomplete/cancelled 集合。
 		// 通用 `event: error` 帧不被识别为终止事件，会导致
 		// "stream closed before response.completed"。
-		if GetInboundEndpoint(c) == EndpointResponses {
+		if inboundIsResponses(c) {
 			if writeResponsesFailedSSE(c, errType, message) {
 				return
 			}
diff --git a/backend/internal/handler/stream_error_event.go b/backend/internal/handler/stream_error_event.go
index 9c6378c2..fc5bf61d 100644
--- a/backend/internal/handler/stream_error_event.go
+++ b/backend/internal/handler/stream_error_event.go
@@ -61,6 +61,36 @@ func writeResponsesFailedSSE(c *gin.Context, errType, message string) bool {
 	return true
 }
 
+// inboundIsResponses 判断当前请求是否落在任何 /responses 路由上。
+//
+// 不能直接用 GetInboundEndpoint(c) == EndpointResponses 比较，因为
+// NormalizeInboundEndpoint 只识别包含 "/v1/responses" 子串的路径；
+// 项目里实际注册了多组路由（gateway_v1、top-level bare、codex direct），
+// 其中 r.POST("/responses", ...) 和 codexDirect.POST("/responses", ...)
+// 的 c.FullPath() 不含 "/v1/" 前缀，会被归一化为原始路径，
+// 导致协议合规终止事件没法发出去。
+//
+// 这里用 FullPath 的后缀判断，覆盖所有变体：
+//   - /v1/responses
+//   - /v1/responses/compact
+//   - /responses
+//   - /responses/compact
+//   - /backend-api/codex/responses
+//   - /backend-api/codex/responses/compact
+func inboundIsResponses(c *gin.Context) bool {
+	if c == nil {
+		return false
+	}
+	p := strings.TrimRight(c.FullPath(), "/")
+	if p == "" && c.Request != nil && c.Request.URL != nil {
+		p = strings.TrimRight(c.Request.URL.Path, "/")
+	}
+	if p == "" {
+		return false
+	}
+	return strings.HasSuffix(p, "/responses") || strings.Contains(p, "/responses/")
+}
+
 // synthesizeResponseID 为合成的 response.failed 事件生成一个稳定的 id。
 // 优先复用 server 端生成的 request_id（存在 request.Context 里，由 request_logger 写入），
 // 以便客户端报错能与 server 日志关联；缺失时回退 uuid。
diff --git a/backend/internal/handler/stream_error_event_test.go b/backend/internal/handler/stream_error_event_test.go
index e1abbc1d..721b5856 100644
--- a/backend/internal/handler/stream_error_event_test.go
+++ b/backend/internal/handler/stream_error_event_test.go
@@ -175,6 +175,57 @@ func TestGatewayHandleStreamingAwareError_MessagesStreamingKeepsLegacy(t *testin
 	assert.True(t, strings.HasPrefix(body, `data: {"type":"error"`), "got: %q", body)
 }
 
+// 项目里 /responses 注册在多组路由：/v1/responses（gateway）、裸 /responses（top-level）、
+// /backend-api/codex/responses（codex direct）。我们 fix 必须覆盖全部，
+// 否则一些客户端走的路径就不会发 response.failed，照样报 stream closed。
+// 这是生产 2026-05-24 ~11:05 UTC user 16 实际命中的 bug。
+func TestInboundIsResponses_CoversAllRoutes(t *testing.T) {
+	cases := []struct {
+		route string
+		want  bool
+	}{
+		{"/v1/responses", true},
+		{"/v1/responses/compact", true},
+		{"/responses", true},                       // <-- 用户 16 实际走这条
+		{"/responses/compact", true},
+		{"/backend-api/codex/responses", true},
+		{"/backend-api/codex/responses/compact", true},
+		{"/v1/chat/completions", false},
+		{"/v1/messages", false},
+		{"/", false},
+		{"/responses-fake", false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.route, func(t *testing.T) {
+			c, _ := newGinContextForEndpoint(t, tc.route)
+			assert.Equal(t, tc.want, inboundIsResponses(c), "route=%q", tc.route)
+		})
+	}
+}
+
+// 用 c.Request.URL.Path 作为 fallback（当 c.FullPath() 为空时，例如某些测试 fixture）。
+func TestInboundIsResponses_FallsBackToURLPath(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodPost, "/responses", nil)
+	// 这种情况下 c.FullPath() 是 ""，必须 fallback 到 URL.Path
+	assert.True(t, inboundIsResponses(c), "URL.Path fallback must work when FullPath is empty")
+}
+
+// 回归生产事故：用户 16 走 /responses 路径，必须发 response.failed。
+func TestOpenAIHandleStreamingAwareError_BareResponsesRouteEmitsResponseFailed(t *testing.T) {
+	c, w := newGinContextForEndpoint(t, "/responses")
+	h := &OpenAIGatewayHandler{}
+	h.handleStreamingAwareError(c, http.StatusTooManyRequests, "rate_limit_error",
+		"Concurrency limit exceeded for user, please retry later", true)
+
+	resp, errObj := parseResponsesFailedSSE(t, w.Body.String())
+	id, _ := resp["id"].(string)
+	assert.True(t, strings.HasPrefix(id, "resp_"))
+	assert.Equal(t, "rate_limit_exceeded", errObj["code"])
+}
+
 // Synthesized response.failed id falls back to uuid when no request_id is present.
 func TestSynthesizeResponseID_FallbackUUID(t *testing.T) {
 	c, _ := newGinContextForEndpoint(t, EndpointResponses)