fix: fall back to tool pods when redis is unavailable

dap-gateway/src/main/java/io/shinhanlife/dap/mcg/presentation/McpRouterController.java

@@ -113,11 +113,16 @@ public class McpRouterController {
     }
 
     private List<ToolMetadata> fetchAllActiveTools() {
-        List<ToolMetadata> activeTools = redisRegistryService.getAllTools()
+        List<ToolMetadata> activeTools = new ArrayList<>();
-                .stream()
+        try {
-                .filter(ToolMetadata::getVisible)
+            activeTools.addAll(redisRegistryService.getAllTools()
-                .collect(Collectors.toList());
+                    .stream()
-                
+                    .filter(ToolMetadata::getVisible)
+                    .collect(Collectors.toList()));
+        } catch (org.springframework.data.redis.RedisConnectionFailureException exception) {
+            log.warn("Redis is unavailable. Fetching tools from configured fallback Tool Pods instead.");
+        }
+
         Set<String> knownTools = activeTools.stream()
                 .map(ToolMetadata::getUid)
                 .collect(Collectors.toSet());

dap-gateway/src/test/java/io/shinhanlife/dap/mcg/presentation/McpRouterControllerTest.java

@@ -0,0 +1,38 @@
+package io.shinhanlife.dap.mcg.presentation;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.when;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.shinhanlife.dap.lib.mcp.security.SecurityProperties;
+import io.shinhanlife.dap.lib.adapter.dto.JsonRpcResponse;
+import io.shinhanlife.dap.mcg.config.GatewayFallbackProperties;
+import io.shinhanlife.dap.mcg.registry.RedisRegistryService;
+import io.shinhanlife.dap.mcg.service.ExecuteService;
+import java.util.List;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+import org.springframework.data.redis.RedisConnectionFailureException;
+import org.springframework.http.ResponseEntity;
+
+class McpRouterControllerTest {
+
+    @Test
+    void returnsEmptyToolListWhenRedisIsUnavailableAndNoFallbackIsConfigured() {
+        RedisRegistryService registryService = org.mockito.Mockito.mock(RedisRegistryService.class);
+        when(registryService.getAllTools()).thenThrow(new RedisConnectionFailureException("Redis unavailable"));
+
+        McpRouterController controller = new McpRouterController(
+                registryService,
+                org.mockito.Mockito.mock(ExecuteService.class),
+                org.mockito.Mockito.mock(SecurityProperties.class),
+                new ObjectMapper(),
+                new GatewayFallbackProperties());
+
+        ResponseEntity<JsonRpcResponse> response = assertDoesNotThrow(() -> controller.listTools(null));
+        Map<?, ?> result = (Map<?, ?>) response.getBody().getResult();
+
+        assertEquals(List.of(), result.get("tools"));
+    }
+}