fix: preserve probe targets on legacy updates

go-backend/internal/http/handler/mutations.go

@@ -886,19 +886,28 @@ func (h *Handler) tunnelUpdate(w http.ResponseWriter, r *http.Request) {
 	}
 	typeVal := asInt(req["type"], 1)
 	ipPreference := asString(req["ipPreference"])
-	probeTarget, probeTargetConfigured, err := parseTunnelProbeTargetFromRequest(req)
-	if err != nil {
-		response.WriteJSON(w, response.ErrDefault(err.Error()))
-		return
-	}
+	_, hasProbeTargetHost := req["probeTargetHost"]
+	_, hasProbeTargetPort := req["probeTargetPort"]
+	probeTargetFieldsPresent := hasProbeTargetHost || hasProbeTargetPort
 	probeTargetHost := ""
 	probeTargetPort := 0
-	if probeTargetConfigured {
-		probeTargetHost = probeTarget.Host
-		probeTargetPort = probeTarget.Port
+	if probeTargetFieldsPresent {
+		probeTarget, probeTargetConfigured, err := parseTunnelProbeTargetFromRequest(req)
+		if err != nil {
+			response.WriteJSON(w, response.ErrDefault(err.Error()))
+			return
+		}
+		if probeTargetConfigured {
+			probeTargetHost = probeTarget.Host
+			probeTargetPort = probeTarget.Port
+		}
 	}
 	oldEntryNodeIDs, _ := h.tunnelEntryNodeIDs(id)
 	oldTunnel, _ := h.getTunnelRecord(id)
+	if !probeTargetFieldsPresent && oldTunnel != nil {
+		probeTargetHost = oldTunnel.ProbeTargetHost
+		probeTargetPort = oldTunnel.ProbeTargetPort
+	}
 	oldChainRows, _ := h.listChainNodesForTunnel(id)
 	if oldTunnel != nil && oldTunnel.Type == 2 && typeVal != 2 {
 		h.cleanupTunnelRuntime(id)

go-backend/internal/http/handler/tunnel_probe_target_api_test.go

@@ -74,6 +74,33 @@ func TestTunnelUpdatePersistsDefaultProbeTargetAsEmpty(t *testing.T) {
 	}
 }
 
+func TestTunnelUpdateWithoutProbeTargetFieldsPreservesExistingTarget(t *testing.T) {
+	h := setupProbeTargetTunnelHandler(t)
+	seedProbeTargetTunnel(t, h, 79, "existing", "old.example.com", 9443)
+	body := bytes.NewReader([]byte(`{
+		"id":79,
+		"name":"existing",
+		"type":1,
+		"flow":1,
+		"trafficRatio":1,
+		"status":1,
+		"inNodeId":[{"nodeId":10,"protocol":"tls"}]
+	}`))
+
+	res := httptest.NewRecorder()
+	h.tunnelUpdate(res, httptest.NewRequest(http.MethodPost, "/api/v1/tunnel/update", body))
+	assertProbeTargetSuccess(t, res)
+
+	items, err := h.repo.ListTunnels()
+	if err != nil {
+		t.Fatalf("list tunnels: %v", err)
+	}
+	item := findProbeTargetTunnelItem(t, items, 79)
+	if item["probeTargetHost"] != "old.example.com" || item["probeTargetPort"] != 9443 {
+		t.Fatalf("expected omitted probe target fields to preserve existing target, got %+v", item)
+	}
+}
+
 func TestTunnelCreateRejectsInvalidProbeTarget(t *testing.T) {
 	h := setupProbeTargetTunnelHandler(t)
 	body := bytes.NewReader([]byte(`{