fix(sidecar): strip ec_transfer_params from decode request in EPD mode

pkg/sidecar/proxy/connector_nixlv2.go

@@ -375,6 +375,7 @@ retryLoop:
 			}
 		}
 	}
+	delete(completionRequest, requestFieldECTransferParams)
 	completionRequest[requestFieldKVTransferParams] = pKVTransferParams
 
 	dbody, err := json.Marshal(completionRequest)

pkg/sidecar/proxy/connector_nixlv2_test.go

@@ -1058,6 +1058,81 @@ var _ = Describe("NIXL Connector (v2)", func() {
 		Expect(testInfo.prefillHandler.GetCompletionHeaders()[0].Get(requestHeaderDataParallelRank)).To(BeEmpty())
 		Expect(testInfo.decodeHandler.GetCompletionHeaders()[0].Get(requestHeaderDataParallelRank)).To(BeEmpty())
 	})
+
+	// EC+PD regression: ec_transfer_params is injected into the prefill request
+	// by the encoder stage but must not appear in the decode request. The decode
+	// pod has no EC connector and vLLM logs a warning when the field is present.
+	It("does not forward ec_transfer_params to the decode request in EPD mode", func() {
+		encoderBackend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(http.StatusOK)
+			_, _ = w.Write([]byte(`{"choices":[],"ec_transfer_params":{"hash-0":{"peer_host":"10.0.0.1"}}}`))
+		}))
+		DeferCleanup(encoderBackend.Close)
+
+		prefillHandler := &mock.ChatCompletionHandler{
+			Connector: KVConnectorNIXLV2,
+			Role:      mock.RolePrefill,
+		}
+		prefillBackend := httptest.NewServer(prefillHandler)
+		DeferCleanup(prefillBackend.Close)
+
+		decodeHandler := &mock.ChatCompletionHandler{
+			Connector: KVConnectorNIXLV2,
+			Role:      mock.RoleDecode,
+		}
+		decodeBackend := httptest.NewServer(decodeHandler)
+		DeferCleanup(decodeBackend.Close)
+
+		decodeURL, err := url.Parse(decodeBackend.URL)
+		Expect(err).ToNot(HaveOccurred())
+
+		cfg := Config{
+			Port:        "0",
+			DecoderURL:  decodeURL,
+			KVConnector: KVConnectorNIXLV2,
+			ECConnector: ECConnectorNIXL,
+		}
+		proxy := NewProxy(cfg)
+
+		ctx, cancelFn := context.WithCancel(newTestContext())
+		stoppedCh := make(chan struct{})
+		DeferCleanup(func() {
+			cancelFn()
+			<-stoppedCh
+		})
+
+		go func() {
+			defer GinkgoRecover()
+			proxy.allowlistValidator = &AllowlistValidator{enabled: false}
+			err := proxy.Start(ctx)
+			Expect(err).ToNot(HaveOccurred())
+			stoppedCh <- struct{}{}
+		}()
+		<-proxy.readyCh
+
+		reqBody, _ := json.Marshal(userMessageRequest(imageURLItem("https://example.com/img.jpg")))
+		req, err := http.NewRequest(http.MethodPost, "http://"+proxy.addr.String()+ChatCompletionsPath, bytes.NewReader(reqBody))
+		Expect(err).ToNot(HaveOccurred())
+		req.Header.Set("Content-Type", "application/json")
+		req.Header.Add(routing.PrefillEndpointHeader, prefillBackend.URL[len("http://"):])
+		req.Header.Add(routing.EncoderEndpointsHeader, encoderBackend.URL[len("http://"):])
+
+		rp, err := http.DefaultClient.Do(req)
+		Expect(err).ToNot(HaveOccurred())
+		defer rp.Body.Close()
+		body, _ := io.ReadAll(rp.Body)
+		Expect(rp.StatusCode).To(Equal(http.StatusOK), string(body))
+
+		Expect(prefillHandler.RequestCount.Load()).To(BeNumerically("==", 1))
+		Expect(decodeHandler.RequestCount.Load()).To(BeNumerically("==", 1))
+
+		prefillReq := prefillHandler.CompletionRequests[0]
+		Expect(prefillReq).To(HaveKey(requestFieldECTransferParams), "prefill request must carry ec_transfer_params")
+
+		decodeReq := decodeHandler.CompletionRequests[0]
+		Expect(decodeReq).ToNot(HaveKey(requestFieldECTransferParams), "decode request must not carry ec_transfer_params")
+	})
 })
 
 // moriProxyEnv bundles a running MoRI-IO proxy with its mock prefill/decode