Fix: Don't expose /mcp/sys route when DIFC is disabled

internal/server/routed.go

@@ -34,11 +34,17 @@ func CreateHTTPServerForRoutedMode(addr string, unifiedServer *UnifiedServer, ap
 	})
 	mux.Handle("/mcp/.well-known/oauth-authorization-server", withResponseLogging(oauthHandler))
 
-	// Create routes for all backends plus sys
-	allBackends := append([]string{"sys"}, unifiedServer.GetServerIDs()...)
+	// Create routes for all backends, plus sys only if DIFC is enabled
+	allBackends := unifiedServer.GetServerIDs()
+	if unifiedServer.IsDIFCEnabled() {
+		allBackends = append([]string{"sys"}, allBackends...)
+		logRouted.Printf("DIFC enabled: including sys in route registration")
+	} else {
+		logRouted.Printf("DIFC disabled: excluding sys from route registration")
+	}
 	logRouted.Printf("Registering routes for %d backends: %v", len(allBackends), allBackends)
 
-	// Create a proxy for each backend server (including sys)
+	// Create a proxy for each backend server (sys included only when DIFC is enabled)
 	for _, serverID := range allBackends {
 		// Capture serverID for the closure
 		backendID := serverID

internal/server/routed_test.go

@@ -367,3 +367,64 @@ func TestRoutedMode_SysToolsBackend_DIFCEnabled(t *testing.T) {
 		}
 	}
 }
+
+func TestRoutedMode_SysRouteNotExposed_DIFCDisabled(t *testing.T) {
+	// When DIFC is disabled (default), /mcp/sys route should NOT be registered
+	cfg := &config.Config{
+		Servers: map[string]*config.ServerConfig{
+			"github": {Command: "docker", Args: []string{}},
+		},
+		// EnableDIFC defaults to false, but explicitly set here for test clarity
+		EnableDIFC: false,
+	}
+
+	ctx := context.Background()
+	us, err := NewUnified(ctx, cfg)
+	require.NoError(t, err, "NewUnified() failed")
+	defer us.Close()
+
+	// Create routed mode server
+	httpServer := CreateHTTPServerForRoutedMode("127.0.0.1:0", us, "")
+
+	// Try to access /mcp/sys route - should get 404
+	req := httptest.NewRequest(http.MethodGet, "/mcp/sys", nil)
+	req.Header.Set("Authorization", "test-session")
+	w := httptest.NewRecorder()
+
+	httpServer.Handler.ServeHTTP(w, req)
+
+	// Should return 404 because the route is not registered
+	if w.Code != http.StatusNotFound {
+		t.Errorf("Expected status 404 for /mcp/sys when DIFC is disabled, got %d", w.Code)
+	}
+}
+
+func TestRoutedMode_SysRouteExposed_DIFCEnabled(t *testing.T) {
+	// When DIFC is enabled, /mcp/sys route SHOULD be registered
+	cfg := &config.Config{
+		Servers: map[string]*config.ServerConfig{
+			"github": {Command: "docker", Args: []string{}},
+		},
+		EnableDIFC: true, // Enable DIFC
+	}
+
+	ctx := context.Background()
+	us, err := NewUnified(ctx, cfg)
+	require.NoError(t, err, "NewUnified() failed")
+	defer us.Close()
+
+	// Create routed mode server
+	httpServer := CreateHTTPServerForRoutedMode("127.0.0.1:0", us, "")
+
+	// Try to access /mcp/sys route - should NOT get 404
+	req := httptest.NewRequest(http.MethodGet, "/mcp/sys", nil)
+	req.Header.Set("Authorization", "test-session")
+	w := httptest.NewRecorder()
+
+	httpServer.Handler.ServeHTTP(w, req)
+
+	// Should NOT return 404 because the route should be registered
+	if w.Code == http.StatusNotFound {
+		t.Errorf("Expected /mcp/sys route to be registered when DIFC is enabled, but got 404")
+	}
+}

internal/server/unified.go

@@ -766,3 +766,8 @@ func (us *UnifiedServer) SetTestMode(enabled bool) {
 func (us *UnifiedServer) ShouldExit() bool {
 	return !us.testMode
 }
+
+// IsDIFCEnabled returns whether DIFC is enabled
+func (us *UnifiedServer) IsDIFCEnabled() bool {
+	return us.enableDIFC
+}