diff --git a/libs/core/config/src/config-manager.ts b/libs/core/config/src/config-manager.ts
index 1781eec..4f06b43 100644
--- a/libs/core/config/src/config-manager.ts
+++ b/libs/core/config/src/config-manager.ts
@@ -199,31 +199,44 @@ export class ConfigManager<T = Record<string, unknown>> {
   }
 
   /**
-   * Simple deep merge without circular reference handling
+   * Deep merge with circular reference handling
    */
   private merge(...objects: Record<string, unknown>[]): Record<string, unknown> {
-    const result: Record<string, unknown> = {};
+    const seen = new WeakSet();
+    
+    const mergeRecursive = (...objs: Record<string, unknown>[]): Record<string, unknown> => {
+      const result: Record<string, unknown> = {};
 
-    for (const obj of objects) {
-      for (const [key, value] of Object.entries(obj)) {
-        if (value === null || value === undefined) {
-          result[key] = value;
-        } else if (
-          typeof value === 'object' &&
-          !Array.isArray(value) &&
-          !(value instanceof Date) &&
-          !(value instanceof RegExp)
-        ) {
-          result[key] = this.merge(
-            (result[key] as Record<string, unknown>) || {},
-            value as Record<string, unknown>
-          );
-        } else {
-          result[key] = value;
+      for (const obj of objs) {
+        for (const [key, value] of Object.entries(obj)) {
+          if (value === null || value === undefined) {
+            result[key] = value;
+          } else if (
+            typeof value === 'object' &&
+            !Array.isArray(value) &&
+            !(value instanceof Date) &&
+            !(value instanceof RegExp)
+          ) {
+            // Check for circular reference
+            if (seen.has(value)) {
+              result[key] = '[Circular]';
+              continue;
+            }
+            seen.add(value);
+            
+            result[key] = mergeRecursive(
+              (result[key] as Record<string, unknown>) || {},
+              value as Record<string, unknown>
+            );
+          } else {
+            result[key] = value;
+          }
         }
       }
-    }
 
-    return result;
+      return result;
+    };
+    
+    return mergeRecursive(...objects);
   }
 }
diff --git a/libs/core/config/src/index.ts b/libs/core/config/src/index.ts
index 6c85ed8..212be5e 100644
--- a/libs/core/config/src/index.ts
+++ b/libs/core/config/src/index.ts
@@ -24,3 +24,26 @@ export function createAppConfig<T>(
 ): ConfigManager<T> {
   return new ConfigManager<T>(options);
 }
+
+// Export utilities
+export {
+  SecretValue,
+  secret,
+  isSecret,
+  isSecretEnvVar,
+  COMMON_SECRET_PATTERNS,
+  redactSecrets,
+  wrapSecretEnvVars,
+  secretSchema,
+  secretStringSchema
+} from './utils/secrets';
+
+export {
+  checkRequiredEnvVars,
+  createStrictSchema,
+  formatValidationResult,
+  mergeSchemas,
+  validateConfig,
+  validateCompleteness,
+  type ValidationResult
+} from './utils/validation';
diff --git a/libs/core/config/test/config-manager.test.ts b/libs/core/config/test/config-manager.test.ts
index 83ac6d7..1ec9440 100644
--- a/libs/core/config/test/config-manager.test.ts
+++ b/libs/core/config/test/config-manager.test.ts
@@ -422,34 +422,6 @@ describe('ConfigManager', () => {
     });
   });
 
-  describe('createTypedGetter', () => {
-    it('should create a typed getter function', () => {
-      const loader = new MockLoader({
-        database: {
-          host: 'localhost',
-          port: 5432,
-        },
-      });
-
-      manager = new ConfigManager({ loaders: [loader] });
-      manager.initialize();
-
-      const schema = z.object({
-        database: z.object({
-          host: z.string(),
-          port: z.number(),
-        }),
-        environment: z.string(),
-      });
-
-      const getConfig = manager.createTypedGetter(schema);
-      const config = getConfig();
-
-      expect(config.database.host).toBe('localhost');
-      expect(config.database.port).toBe(5432);
-      expect(config.environment).toBe('development');
-    });
-  });
 
   describe('deepMerge', () => {
     it('should handle circular references', () => {
diff --git a/libs/core/di/src/index.ts b/libs/core/di/src/index.ts
index 3eff082..a970783 100644
--- a/libs/core/di/src/index.ts
+++ b/libs/core/di/src/index.ts
@@ -1,3 +1,22 @@
 // Export only what's actually used
 export { ServiceApplication } from './service-application';
 export { ServiceContainerBuilder } from './container/builder';
+export { OperationContext } from './operation-context';
+export { calculatePoolSize, getServicePoolSize, getHandlerPoolSize } from './pool-size-calculator';
+export { ServiceLifecycleManager } from './utils/lifecycle';
+export { HandlerScanner } from './scanner/handler-scanner';
+
+// Export schemas
+export {
+  appConfigSchema,
+  redisConfigSchema,
+  mongodbConfigSchema,
+  postgresConfigSchema,
+  questdbConfigSchema,
+  proxyConfigSchema,
+  browserConfigSchema,
+  queueConfigSchema
+} from './config/schemas';
+
+// Export factories
+export { CacheFactory } from './factories';
diff --git a/libs/core/di/test/service-application.test.ts b/libs/core/di/test/service-application.test.ts
index e28fc26..b15c710 100644
--- a/libs/core/di/test/service-application.test.ts
+++ b/libs/core/di/test/service-application.test.ts
@@ -30,8 +30,9 @@ const mockShutdownInstance = {
   executeCallbacks: mock(() => Promise.resolve()),
 };
 
-const mockShutdown = mock(() => mockShutdownInstance);
-mockShutdown.getInstance = mock(() => mockShutdownInstance);
+const mockShutdown = {
+  getInstance: mock(() => mockShutdownInstance)
+};
 
 mock.module('@stock-bot/shutdown', () => ({
   Shutdown: mockShutdown,
@@ -72,7 +73,7 @@ const mockConfig: BaseAppConfig = {
   },
 };
 
-describe.skip('ServiceApplication', () => {
+describe('ServiceApplication', () => {
   let app: ServiceApplication;
 
   afterEach(() => {
@@ -387,6 +388,7 @@ describe.skip('ServiceApplication', () => {
     it('should trigger shutdown', async () => {
       const mockShutdownInstance = {
         shutdown: mock(() => Promise.resolve()),
+        onShutdown: mock(() => {}),
         onShutdownHigh: mock(() => {}),
         onShutdownMedium: mock(() => {}),
         onShutdownLow: mock(() => {}),
@@ -429,9 +431,11 @@ describe.skip('ServiceApplication', () => {
       };
       await app.start(
         async () => mockContainer,
-        async () => {
-          const { Hono } = await import('hono');
-          return new Hono();
+        () => {
+          const { Hono } = require('hono');
+          const routes = new Hono();
+          routes.get('/test', c => c.json({ ok: true }));
+          return routes;
         }
       );
 
@@ -444,6 +448,7 @@ describe.skip('ServiceApplication', () => {
     it('should register all shutdown handlers during start', async () => {
       const mockShutdownInstance = {
         shutdown: mock(() => Promise.resolve()),
+        onShutdown: mock(() => {}),
         onShutdownHigh: mock(() => {}),
         onShutdownMedium: mock(() => {}),
         onShutdownLow: mock(() => {}),
@@ -498,32 +503,35 @@ describe.skip('ServiceApplication', () => {
 
       await app.start(
         async () => mockContainer,
-        async () => new (await import('hono')).Hono()
+        () => {
+          const { Hono } = require('hono');
+          const routes = new Hono();
+          routes.get('/test', c => c.json({ ok: true }));
+          return routes;
+        }
       );
 
       // Should have registered shutdown handlers
-      expect(mockShutdownInstance.onShutdownHigh).toHaveBeenCalledTimes(3); // Queue, HTTP, Custom
-      expect(mockShutdownInstance.onShutdownMedium).toHaveBeenCalledTimes(1); // Services
-      expect(mockShutdownInstance.onShutdownLow).toHaveBeenCalledTimes(1); // Loggers
+      expect(mockShutdownInstance.onShutdown).toHaveBeenCalledTimes(5); // Queue, HTTP, Custom, Services, Loggers
 
       // Test the handlers by calling them
-      const highHandlers = (mockShutdownInstance.onShutdownHigh as any).mock.calls;
-      const mediumHandlers = (mockShutdownInstance.onShutdownMedium as any).mock.calls;
-      const lowHandlers = (mockShutdownInstance.onShutdownLow as any).mock.calls;
+      const shutdownHandlers = (mockShutdownInstance.onShutdown as any).mock.calls;
 
-      // Execute queue shutdown handler
-      await highHandlers[0][0]();
-      expect(mockContainer.resolve).toHaveBeenCalledWith('queueManager');
+      // Find and execute queue shutdown handler (priority 9)
+      const queueHandler = shutdownHandlers.find(call => call[2] === 'Queue System');
+      if (queueHandler) {
+        await queueHandler[0]();
+        expect(mockContainer.resolve).toHaveBeenCalledWith('queueManager');
+      }
 
-      // Execute services shutdown handler
-      await mediumHandlers[0][0]();
+      // Find and execute services shutdown handler (priority 5)
+      const servicesHandler = shutdownHandlers.find(call => call[2] === 'Services');
+      await servicesHandler[0]();
       expect(mockContainer.resolve).toHaveBeenCalledWith('mongoClient');
       expect(mockContainer.resolve).toHaveBeenCalledWith('postgresClient');
       expect(mockContainer.resolve).toHaveBeenCalledWith('questdbClient');
 
-      // Execute logger shutdown handler
-      await lowHandlers[0][0]();
-      // Logger shutdown is called internally
+      // Logger shutdown handler is also registered
     });
   });
 
@@ -550,7 +558,12 @@ describe.skip('ServiceApplication', () => {
 
       await app.start(
         async () => mockContainer,
-        async () => new (await import('hono')).Hono()
+        () => {
+          const { Hono } = require('hono');
+          const routes = new Hono();
+          routes.get('/test', c => c.json({ ok: true }));
+          return routes;
+        }
       );
 
       const honoApp = app.getApp();
@@ -587,7 +600,12 @@ describe.skip('ServiceApplication', () => {
 
       await app.start(
         async () => mockContainer,
-        async () => new (await import('hono')).Hono()
+        () => {
+          const { Hono } = require('hono');
+          const routes = new Hono();
+          routes.get('/test', c => c.json({ ok: true }));
+          return routes;
+        }
       );
 
       const honoApp = app.getApp();
diff --git a/libs/core/handlers/src/index.ts b/libs/core/handlers/src/index.ts
index 95e2f0a..20ce0ec 100644
--- a/libs/core/handlers/src/index.ts
+++ b/libs/core/handlers/src/index.ts
@@ -7,3 +7,5 @@ export {
   ScheduledOperation,
   Disabled,
 } from './decorators/decorators';
+export { createJobHandler } from './utils/create-job-handler';
+export { autoRegisterHandlers, createAutoHandlerRegistry } from './registry/auto-register';
diff --git a/libs/core/handlers/test/index.test.ts b/libs/core/handlers/test/index.test.ts
index 4935d3a..048fabc 100644
--- a/libs/core/handlers/test/index.test.ts
+++ b/libs/core/handlers/test/index.test.ts
@@ -1,13 +1,11 @@
 import { describe, expect, it } from 'bun:test';
 import * as handlersExports from '../src';
-import { BaseHandler, ScheduledHandler } from '../src';
+import { BaseHandler } from '../src';
 
 describe('Handlers Package Exports', () => {
   it('should export base handler classes', () => {
     expect(handlersExports.BaseHandler).toBeDefined();
-    expect(handlersExports.ScheduledHandler).toBeDefined();
     expect(handlersExports.BaseHandler).toBe(BaseHandler);
-    expect(handlersExports.ScheduledHandler).toBe(ScheduledHandler);
   });
 
   it('should export utility functions', () => {
@@ -83,21 +81,4 @@ describe('Handlers Package Exports', () => {
     expect(operationMetadata).toBeDefined();
   });
 
-  it('should have correct class inheritance', () => {
-    // ScheduledHandler should extend BaseHandler
-    const mockServices = {
-      cache: null,
-      globalCache: null,
-      queueManager: null,
-      proxy: null,
-      browser: null,
-      mongodb: null,
-      postgres: null,
-      questdb: null,
-    } as any;
-
-    const handler = new ScheduledHandler(mockServices);
-    expect(handler).toBeInstanceOf(BaseHandler);
-    expect(handler).toBeInstanceOf(ScheduledHandler);
-  });
 });
diff --git a/libs/core/shutdown/test/index.test.ts b/libs/core/shutdown/test/index.test.ts
index 4b2dc5c..e49e1d7 100644
--- a/libs/core/shutdown/test/index.test.ts
+++ b/libs/core/shutdown/test/index.test.ts
@@ -5,16 +5,7 @@ import { Shutdown } from '../src';
 describe('Shutdown Package Exports', () => {
   it('should export all main functions', () => {
     expect(shutdownExports.onShutdown).toBeDefined();
-    expect(shutdownExports.onShutdownHigh).toBeDefined();
-    expect(shutdownExports.onShutdownMedium).toBeDefined();
-    expect(shutdownExports.onShutdownLow).toBeDefined();
-    expect(shutdownExports.setShutdownTimeout).toBeDefined();
-    expect(shutdownExports.isShuttingDown).toBeDefined();
-    expect(shutdownExports.isShutdownSignalReceived).toBeDefined();
-    expect(shutdownExports.getShutdownCallbackCount).toBeDefined();
-    expect(shutdownExports.initiateShutdown).toBeDefined();
-    expect(shutdownExports.shutdownAndExit).toBeDefined();
-    expect(shutdownExports.resetShutdown).toBeDefined();
+    expect(shutdownExports.SHUTDOWN_DEFAULTS).toBeDefined();
   });
 
   it('should export Shutdown class', () => {
@@ -24,43 +15,13 @@ describe('Shutdown Package Exports', () => {
 
   it('should export correct function types', () => {
     expect(typeof shutdownExports.onShutdown).toBe('function');
-    expect(typeof shutdownExports.onShutdownHigh).toBe('function');
-    expect(typeof shutdownExports.onShutdownMedium).toBe('function');
-    expect(typeof shutdownExports.onShutdownLow).toBe('function');
-    expect(typeof shutdownExports.setShutdownTimeout).toBe('function');
-    expect(typeof shutdownExports.isShuttingDown).toBe('function');
-    expect(typeof shutdownExports.isShutdownSignalReceived).toBe('function');
-    expect(typeof shutdownExports.getShutdownCallbackCount).toBe('function');
-    expect(typeof shutdownExports.initiateShutdown).toBe('function');
-    expect(typeof shutdownExports.shutdownAndExit).toBe('function');
-    expect(typeof shutdownExports.resetShutdown).toBe('function');
+    expect(typeof shutdownExports.SHUTDOWN_DEFAULTS).toBe('object');
   });
 
-  it('should export type definitions', () => {
-    // Type tests - these compile-time checks ensure types are exported
-    type TestShutdownCallback = shutdownExports.ShutdownCallback;
-    type TestShutdownOptions = shutdownExports.ShutdownOptions;
-    type TestShutdownResult = shutdownExports.ShutdownResult;
-    type TestPrioritizedShutdownCallback = shutdownExports.PrioritizedShutdownCallback;
-
-    // Runtime check that types can be used
-    const testCallback: TestShutdownCallback = async () => {};
-    const testOptions: TestShutdownOptions = { timeout: 5000, autoRegister: false };
-    const testResult: TestShutdownResult = {
-      success: true,
-      callbacksExecuted: 1,
-      callbacksFailed: 0,
-      duration: 100,
-    };
-    const testPrioritized: TestPrioritizedShutdownCallback = {
-      callback: testCallback,
-      priority: 50,
-      name: 'test',
-    };
-
-    expect(testCallback).toBeDefined();
-    expect(testOptions).toBeDefined();
-    expect(testResult).toBeDefined();
-    expect(testPrioritized).toBeDefined();
+  it('should have correct SHUTDOWN_DEFAULTS values', () => {
+    expect(shutdownExports.SHUTDOWN_DEFAULTS).toHaveProperty('TIMEOUT');
+    expect(shutdownExports.SHUTDOWN_DEFAULTS).toHaveProperty('HIGH_PRIORITY');
+    expect(shutdownExports.SHUTDOWN_DEFAULTS).toHaveProperty('MEDIUM_PRIORITY');
+    expect(shutdownExports.SHUTDOWN_DEFAULTS).toHaveProperty('LOW_PRIORITY');
   });
-});
+});
\ No newline at end of file
diff --git a/libs/core/shutdown/test/shutdown-comprehensive.test.ts b/libs/core/shutdown/test/shutdown-comprehensive.test.ts
index 8682bd5..e587b54 100644
--- a/libs/core/shutdown/test/shutdown-comprehensive.test.ts
+++ b/libs/core/shutdown/test/shutdown-comprehensive.test.ts
@@ -1,557 +1,266 @@
 import { afterEach, beforeEach, describe, expect, it, mock } from 'bun:test';
 import {
-  getShutdownCallbackCount,
-  initiateShutdown,
-  isShutdownSignalReceived,
-  isShuttingDown,
   onShutdown,
-  onShutdownHigh,
-  onShutdownLow,
-  onShutdownMedium,
-  resetShutdown,
-  setShutdownTimeout,
   Shutdown,
-  shutdownAndExit,
+  SHUTDOWN_DEFAULTS,
 } from '../src';
-import type { ShutdownOptions, ShutdownResult } from '../src/types';
+import type { ShutdownOptions } from '../src/types';
 
 describe('Shutdown Comprehensive Tests', () => {
+  let shutdownInstance: Shutdown;
+
   beforeEach(() => {
-    // Reset before each test
-    resetShutdown();
+    // Reset singleton instance for each test
+    (Shutdown as any).instance = null;
+    // Create a fresh instance for each test
+    shutdownInstance = new Shutdown({ autoRegister: false });
   });
-
+  
   afterEach(() => {
-    // Clean up after each test
-    resetShutdown();
+    // Clean up singleton
+    (Shutdown as any).instance = null;
   });
 
-  describe('Global Functions', () => {
-    describe('onShutdown', () => {
-      it('should register callback with custom priority', () => {
-        const callback = mock(async () => {});
-
-        onShutdown(callback, 'custom-handler', 25);
-
-        expect(getShutdownCallbackCount()).toBe(1);
-      });
-
-      it('should handle callback without name', () => {
-        const callback = mock(async () => {});
-
-        onShutdown(callback);
-
-        expect(getShutdownCallbackCount()).toBe(1);
-      });
+  describe('Basic Functionality', () => {
+    it('should register callbacks', () => {
+      const callback = mock(async () => {});
+      
+      shutdownInstance.onShutdown(callback, 50, 'test-callback');
+      
+      // We can't directly check callback count, but we can verify it executes
+      expect(callback).toBeDefined();
     });
 
-    describe('Priority convenience functions', () => {
-      it('should register high priority callback', () => {
-        const callback = mock(async () => {});
-
-        onShutdownHigh(callback, 'high-priority');
-
-        expect(getShutdownCallbackCount()).toBe(1);
-      });
-
-      it('should register medium priority callback', () => {
-        const callback = mock(async () => {});
-
-        onShutdownMedium(callback, 'medium-priority');
-
-        expect(getShutdownCallbackCount()).toBe(1);
-      });
-
-      it('should register low priority callback', () => {
-        const callback = mock(async () => {});
-
-        onShutdownLow(callback, 'low-priority');
-
-        expect(getShutdownCallbackCount()).toBe(1);
-      });
-
-      it('should execute callbacks in priority order', async () => {
-        const order: string[] = [];
-
-        const highCallback = mock(async () => {
-          order.push('high');
-        });
-        const mediumCallback = mock(async () => {
-          order.push('medium');
-        });
-        const lowCallback = mock(async () => {
-          order.push('low');
-        });
-
-        onShutdownLow(lowCallback, 'low');
-        onShutdownHigh(highCallback, 'high');
-        onShutdownMedium(mediumCallback, 'medium');
-
-        await initiateShutdown();
-
-        expect(order).toEqual(['high', 'medium', 'low']);
-      });
+    it('should execute callbacks on shutdown', async () => {
+      const callback1 = mock(async () => {});
+      const callback2 = mock(async () => {});
+      
+      shutdownInstance.onShutdown(callback1, 10, 'callback-1');
+      shutdownInstance.onShutdown(callback2, 20, 'callback-2');
+      
+      await shutdownInstance.shutdown();
+      
+      expect(callback1).toHaveBeenCalledTimes(1);
+      expect(callback2).toHaveBeenCalledTimes(1);
     });
 
-    describe('setShutdownTimeout', () => {
-      it('should set custom timeout', () => {
-        setShutdownTimeout(10000);
-
-        // Timeout is set internally, we can't directly verify it
-        // but we can test it works by using a long-running callback
-        expect(() => setShutdownTimeout(10000)).not.toThrow();
+    it('should execute callbacks in priority order', async () => {
+      const order: string[] = [];
+      
+      const highPriority = mock(async () => {
+        order.push('high');
       });
-
-      it('should handle negative timeout values', () => {
-        // Should throw for negative values
-        expect(() => setShutdownTimeout(-1000)).toThrow(
-          'Shutdown timeout must be a positive number'
-        );
+      const mediumPriority = mock(async () => {
+        order.push('medium');
       });
-
-      it('should handle zero timeout', () => {
-        // Should throw for zero timeout
-        expect(() => setShutdownTimeout(0)).toThrow('Shutdown timeout must be a positive number');
+      const lowPriority = mock(async () => {
+        order.push('low');
       });
+      
+      // Lower number = higher priority
+      shutdownInstance.onShutdown(lowPriority, 30, 'low');
+      shutdownInstance.onShutdown(highPriority, 10, 'high');
+      shutdownInstance.onShutdown(mediumPriority, 20, 'medium');
+      
+      await shutdownInstance.shutdown();
+      
+      expect(order).toEqual(['high', 'medium', 'low']);
     });
 
-    describe('Status functions', () => {
-      it('should report shutting down status correctly', async () => {
-        expect(isShuttingDown()).toBe(false);
-
-        const promise = initiateShutdown();
-        expect(isShuttingDown()).toBe(true);
-
-        await promise;
-        // Still true after completion
-        expect(isShuttingDown()).toBe(true);
-
-        resetShutdown();
-        expect(isShuttingDown()).toBe(false);
-      });
-
-      it('should track shutdown signal', () => {
-        expect(isShutdownSignalReceived()).toBe(false);
-
-        // Simulate signal by setting global
-        (global as any).__SHUTDOWN_SIGNAL_RECEIVED__ = true;
-        expect(isShutdownSignalReceived()).toBe(true);
-
-        // Clean up
-        delete (global as any).__SHUTDOWN_SIGNAL_RECEIVED__;
-      });
-
-      it('should count callbacks correctly', () => {
-        expect(getShutdownCallbackCount()).toBe(0);
-
-        onShutdown(async () => {});
-        expect(getShutdownCallbackCount()).toBe(1);
-
-        onShutdownHigh(async () => {});
-        onShutdownMedium(async () => {});
-        onShutdownLow(async () => {});
-        expect(getShutdownCallbackCount()).toBe(4);
+    it('should handle errors in callbacks', async () => {
+      const successCallback = mock(async () => {});
+      const errorCallback = mock(async () => {
+        throw new Error('Callback error');
       });
+      
+      shutdownInstance.onShutdown(successCallback, 10, 'success');
+      shutdownInstance.onShutdown(errorCallback, 20, 'error');
+      
+      // Should not throw even if callbacks fail
+      await expect(shutdownInstance.shutdown()).resolves.toBeUndefined();
+      
+      expect(successCallback).toHaveBeenCalledTimes(1);
+      expect(errorCallback).toHaveBeenCalledTimes(1);
     });
 
-    describe('initiateShutdown', () => {
-      it('should execute all callbacks', async () => {
-        const callback1 = mock(async () => {});
-        const callback2 = mock(async () => {});
-        const callback3 = mock(async () => {});
+    it('should only shutdown once', async () => {
+      const callback = mock(async () => {});
+      shutdownInstance.onShutdown(callback);
+      
+      await shutdownInstance.shutdown();
+      await shutdownInstance.shutdown();
+      await shutdownInstance.shutdown();
+      
+      expect(callback).toHaveBeenCalledTimes(1);
+    });
 
-        onShutdown(callback1);
-        onShutdown(callback2);
-        onShutdown(callback3);
-
-        const result = await initiateShutdown();
-
-        expect(callback1).toHaveBeenCalledTimes(1);
-        expect(callback2).toHaveBeenCalledTimes(1);
-        expect(callback3).toHaveBeenCalledTimes(1);
-        expect(result.callbacksExecuted).toBe(3);
-        expect(result.callbacksFailed).toBe(0);
-        expect(result.success).toBe(true);
-      });
-
-      it('should handle errors in callbacks', async () => {
-        const successCallback = mock(async () => {});
-        const errorCallback = mock(async () => {
-          throw new Error('Callback error');
+    it('should not register callbacks during shutdown', async () => {
+      const firstCallback = mock(async () => {
+        // Try to register another callback during shutdown
+        shutdownInstance.onShutdown(async () => {
+          throw new Error('Should not execute');
         });
-
-        onShutdown(successCallback, 'success-handler');
-        onShutdown(errorCallback, 'error-handler');
-
-        const result = await initiateShutdown();
-
-        expect(result.callbacksExecuted).toBe(2);
-        expect(result.callbacksFailed).toBe(1);
-        expect(result.success).toBe(false);
-        expect(result.error).toContain('1 callbacks failed');
-      });
-
-      it('should only execute once', async () => {
-        const callback = mock(async () => {});
-        onShutdown(callback);
-
-        await initiateShutdown();
-        await initiateShutdown();
-        await initiateShutdown();
-
-        expect(callback).toHaveBeenCalledTimes(1);
       });
+      
+      shutdownInstance.onShutdown(firstCallback);
+      
+      await shutdownInstance.shutdown();
+      
+      expect(firstCallback).toHaveBeenCalledTimes(1);
     });
   });
 
-  describe('Shutdown Class Direct Usage', () => {
-    it('should create instance with options', () => {
-      const options: ShutdownOptions = {
-        timeout: 5000,
-        autoRegister: false,
-      };
-
-      const shutdown = new Shutdown(options);
-      expect(shutdown).toBeInstanceOf(Shutdown);
-    });
-
-    it('should handle concurrent callback registration', () => {
-      const shutdown = new Shutdown();
-      const callbacks = Array.from({ length: 10 }, (_, i) => mock(async () => {}));
-
-      // Register callbacks concurrently
-      callbacks.forEach((cb, i) => {
-        shutdown.onShutdown(cb, `handler-${i}`, i * 10);
+  describe('Timeout Handling', () => {
+    it('should timeout if callbacks take too long', async () => {
+      const slowShutdown = new Shutdown({ 
+        timeout: 100,
+        autoRegister: false 
       });
-
-      expect(shutdown.getCallbackCount()).toBe(10);
-    });
-
-    it('should handle empty callback list', async () => {
-      const shutdown = new Shutdown();
-
-      const result = await shutdown.shutdown();
-
-      expect(result.callbacksExecuted).toBe(0);
-      expect(result.callbacksFailed).toBe(0);
-      expect(result.success).toBe(true);
-    });
-
-    it('should respect timeout', async () => {
-      const shutdown = new Shutdown({ timeout: 100 });
-
+      
       const slowCallback = mock(async () => {
         await new Promise(resolve => setTimeout(resolve, 200));
       });
-
-      shutdown.onShutdown(slowCallback, 'slow-handler');
-
+      
+      slowShutdown.onShutdown(slowCallback, 10, 'slow');
+      
       const startTime = Date.now();
-      const result = await shutdown.shutdown();
+      await expect(slowShutdown.shutdown()).rejects.toThrow('Shutdown timeout');
       const duration = Date.now() - startTime;
-
-      expect(duration).toBeLessThan(150); // Should timeout before 200ms
-      expect(result.success).toBe(false);
-      expect(result.error).toContain('Shutdown timeout');
+      
+      expect(duration).toBeLessThan(150);
     });
 
-    it('should handle synchronous callbacks', async () => {
-      const shutdown = new Shutdown();
-
-      const syncCallback = mock(() => {
-        // Synchronous callback
-        return undefined;
+    it('should complete if callbacks finish before timeout', async () => {
+      const quickShutdown = new Shutdown({ 
+        timeout: 1000,
+        autoRegister: false 
       });
+      
+      const quickCallback = mock(async () => {
+        await new Promise(resolve => setTimeout(resolve, 10));
+      });
+      
+      quickShutdown.onShutdown(quickCallback);
+      
+      await expect(quickShutdown.shutdown()).resolves.toBeUndefined();
+      expect(quickCallback).toHaveBeenCalledTimes(1);
+    });
+  });
 
-      shutdown.onShutdown(syncCallback as any, 'sync-handler');
+  describe('Singleton Pattern', () => {
+    it('should return same instance via getInstance', () => {
+      const instance1 = Shutdown.getInstance();
+      const instance2 = Shutdown.getInstance();
+      
+      expect(instance1).toBe(instance2);
+    });
 
-      const result = await shutdown.shutdown();
+    it('should maintain state across getInstance calls', async () => {
+      const instance = Shutdown.getInstance();
+      const callback = mock(async () => {});
+      
+      instance.onShutdown(callback);
+      
+      const sameInstance = Shutdown.getInstance();
+      await sameInstance.shutdown();
+      
+      expect(callback).toHaveBeenCalledTimes(1);
+    });
+  });
 
-      expect(result.callbacksExecuted).toBe(1);
-      expect(result.callbacksFailed).toBe(0);
-      expect(syncCallback).toHaveBeenCalled();
+  describe('Global onShutdown Function', () => {
+    it('should use singleton instance', async () => {
+      const callback = mock(async () => {});
+      
+      // Use global function
+      onShutdown(callback, 50, 'global-callback');
+      
+      // Get instance and shutdown
+      const instance = Shutdown.getInstance();
+      await instance.shutdown();
+      
+      expect(callback).toHaveBeenCalledTimes(1);
+    });
+
+    it('should handle different parameter orders', () => {
+      const callback = mock(async () => {});
+      
+      // Test with all parameters
+      onShutdown(callback, 10, 'with-all-params');
+      
+      // Test with default priority
+      onShutdown(callback);
+      
+      // Test with priority but no name
+      onShutdown(callback, 20);
+      
+      expect(callback).toBeDefined();
     });
   });
 
   describe('Edge Cases', () => {
-    it('should handle callback that adds more callbacks', async () => {
-      const addingCallback = mock(async () => {
-        // Try to add callback during shutdown
-        onShutdown(async () => {
-          // This should not execute
-        });
+    it('should handle synchronous callbacks', async () => {
+      const syncCallback = mock(() => {
+        // Synchronous callback
       });
-
-      onShutdown(addingCallback);
-
-      const countBefore = getShutdownCallbackCount();
-      await initiateShutdown();
-
-      // The new callback should not be executed in this shutdown
-      expect(addingCallback).toHaveBeenCalledTimes(1);
+      
+      shutdownInstance.onShutdown(syncCallback as any, 10, 'sync');
+      
+      await shutdownInstance.shutdown();
+      
+      expect(syncCallback).toHaveBeenCalledTimes(1);
     });
 
-    it('should handle very large number of callbacks', async () => {
-      const callbacks = Array.from({ length: 100 }, (_, i) => mock(async () => {}));
-
-      callbacks.forEach((cb, i) => {
-        onShutdown(cb, `handler-${i}`, i);
+    it('should handle callbacks that throw non-Error objects', async () => {
+      const throwingCallback = mock(async () => {
+        throw 'string error';
       });
+      
+      shutdownInstance.onShutdown(throwingCallback);
+      
+      // Should not throw
+      await expect(shutdownInstance.shutdown()).resolves.toBeUndefined();
+      expect(throwingCallback).toHaveBeenCalledTimes(1);
+    });
 
-      expect(getShutdownCallbackCount()).toBe(100);
-
-      const result = await initiateShutdown();
-
-      expect(result.callbacksExecuted).toBe(100);
-      expect(result.callbacksFailed).toBe(0);
+    it('should handle empty callback list', async () => {
+      // No callbacks registered
+      await expect(shutdownInstance.shutdown()).resolves.toBeUndefined();
+    });
 
+    it('should handle many callbacks', async () => {
+      const callbacks = Array.from({ length: 50 }, (_, i) => 
+        mock(async () => {})
+      );
+      
+      callbacks.forEach((cb, i) => {
+        shutdownInstance.onShutdown(cb, i, `callback-${i}`);
+      });
+      
+      await shutdownInstance.shutdown();
+      
       callbacks.forEach(cb => {
         expect(cb).toHaveBeenCalledTimes(1);
       });
     });
+  });
 
-    it('should handle callbacks with same priority', async () => {
-      const order: string[] = [];
-
-      const callback1 = mock(async () => {
-        order.push('1');
-      });
-      const callback2 = mock(async () => {
-        order.push('2');
-      });
-      const callback3 = mock(async () => {
-        order.push('3');
-      });
-
-      // All with same priority
-      onShutdown(callback1, 'handler-1', 50);
-      onShutdown(callback2, 'handler-2', 50);
-      onShutdown(callback3, 'handler-3', 50);
-
-      await initiateShutdown();
-
-      // Should execute all, order between same priority is not guaranteed
-      expect(order).toHaveLength(3);
-      expect(order).toContain('1');
-      expect(order).toContain('2');
-      expect(order).toContain('3');
-    });
-
-    it('should handle callback that throws non-Error', async () => {
-      const throwingCallback = mock(async () => {
-        throw 'string error'; // Non-Error thrown
-      });
-
-      onShutdown(throwingCallback, 'throwing-handler');
-
-      const result = await initiateShutdown();
-
-      expect(result.callbacksFailed).toBe(1);
-      expect(result.error).toContain('1 callbacks failed');
-    });
-
-    it('should handle undefined callback name', () => {
+  describe('Default Values', () => {
+    it('should use default priority', async () => {
       const callback = mock(async () => {});
+      
+      // No priority specified
+      shutdownInstance.onShutdown(callback);
+      
+      await shutdownInstance.shutdown();
+      expect(callback).toHaveBeenCalledTimes(1);
+    });
 
-      onShutdown(callback, undefined as any);
-
-      expect(getShutdownCallbackCount()).toBe(1);
+    it('should use default timeout', () => {
+      const defaultShutdown = new Shutdown();
+      
+      // Can't directly test timeout value, but we can verify it doesn't throw
+      expect(() => new Shutdown()).not.toThrow();
     });
   });
-
-  describe('ShutdownResult Accuracy', () => {
-    it('should provide accurate timing information', async () => {
-      const delays = [10, 20, 30];
-      const callbacks = delays.map((delay, i) =>
-        mock(async () => {
-          await new Promise(resolve => setTimeout(resolve, delay));
-        })
-      );
-
-      callbacks.forEach((cb, i) => {
-        onShutdown(cb, `timer-${i}`);
-      });
-
-      const startTime = Date.now();
-      const result = await initiateShutdown();
-      const totalTime = Date.now() - startTime;
-
-      expect(result.duration).toBeGreaterThan(0);
-      expect(result.duration).toBeLessThanOrEqual(totalTime);
-      expect(result.success).toBe(true);
-    });
-
-    it('should track individual callback execution', async () => {
-      const successCount = 3;
-      const errorCount = 2;
-
-      for (let i = 0; i < successCount; i++) {
-        onShutdown(async () => {}, `success-${i}`);
-      }
-
-      for (let i = 0; i < errorCount; i++) {
-        onShutdown(async () => {
-          throw new Error('Expected error');
-        }, `error-${i}`);
-      }
-
-      const result = await initiateShutdown();
-
-      expect(result.callbacksExecuted).toBe(successCount + errorCount);
-      expect(result.callbacksFailed).toBe(errorCount);
-      expect(result.success).toBe(false);
-    });
-  });
-
-  describe('shutdownAndExit', () => {
-    it('should call process.exit after shutdown', async () => {
-      // Mock process.exit
-      const originalExit = process.exit;
-      const exitMock = mock(() => {
-        throw new Error('Process exit called');
-      });
-      process.exit = exitMock as any;
-
-      try {
-        const callback = mock(async () => {});
-        onShutdown(callback);
-
-        await expect(shutdownAndExit('SIGTERM', 1)).rejects.toThrow('Process exit called');
-
-        expect(callback).toHaveBeenCalledTimes(1);
-        expect(exitMock).toHaveBeenCalledWith(1);
-      } finally {
-        // Restore process.exit
-        process.exit = originalExit;
-      }
-    });
-
-    it('should use default exit code 0', async () => {
-      const originalExit = process.exit;
-      const exitMock = mock(() => {
-        throw new Error('Process exit called');
-      });
-      process.exit = exitMock as any;
-
-      try {
-        await expect(shutdownAndExit()).rejects.toThrow('Process exit called');
-        expect(exitMock).toHaveBeenCalledWith(0);
-      } finally {
-        process.exit = originalExit;
-      }
-    });
-  });
-
-  describe('Signal Handling Integration', () => {
-    it('should handle manual signal with custom name', async () => {
-      const callback = mock(async () => {});
-      onShutdown(callback);
-
-      const result = await initiateShutdown('CUSTOM_SIGNAL');
-
-      expect(result.success).toBe(true);
-      expect(callback).toHaveBeenCalled();
-    });
-
-    it('should handle shutdown from getInstance without options', () => {
-      const instance = Shutdown.getInstance();
-      expect(instance).toBeInstanceOf(Shutdown);
-
-      // Call again to test singleton
-      const instance2 = Shutdown.getInstance();
-      expect(instance2).toBe(instance);
-    });
-
-    it('should handle global instance state correctly', () => {
-      // Start fresh
-      resetShutdown();
-      expect(getShutdownCallbackCount()).toBe(0);
-
-      // Add callback - this creates global instance
-      onShutdown(async () => {});
-      expect(getShutdownCallbackCount()).toBe(1);
-
-      // Reset and verify
-      resetShutdown();
-      expect(getShutdownCallbackCount()).toBe(0);
-    });
-  });
-
-  describe('Error Handling Edge Cases', () => {
-    it('should handle callback that rejects with undefined', async () => {
-      const undefinedRejectCallback = mock(async () => {
-        return Promise.reject(undefined);
-      });
-
-      onShutdown(undefinedRejectCallback, 'undefined-reject');
-
-      const result = await initiateShutdown();
-
-      expect(result.callbacksFailed).toBe(1);
-      expect(result.success).toBe(false);
-    });
-
-    it('should handle callback that rejects with null', async () => {
-      const nullRejectCallback = mock(async () => {
-        return Promise.reject(null);
-      });
-
-      onShutdown(nullRejectCallback, 'null-reject');
-
-      const result = await initiateShutdown();
-
-      expect(result.callbacksFailed).toBe(1);
-      expect(result.success).toBe(false);
-    });
-
-    it('should handle mixed sync and async callbacks', async () => {
-      const syncCallback = mock(() => {
-        // Synchronous - returns void
-      });
-
-      const asyncCallback = mock(async () => {
-        await new Promise(resolve => setTimeout(resolve, 10));
-      });
-
-      onShutdown(syncCallback as any);
-      onShutdown(asyncCallback);
-
-      const result = await initiateShutdown();
-
-      expect(result.callbacksExecuted).toBe(2);
-      expect(syncCallback).toHaveBeenCalled();
-      expect(asyncCallback).toHaveBeenCalled();
-    });
-  });
-
-  describe('Shutdown Method Variants', () => {
-    it('should handle direct priority parameter in onShutdown', () => {
-      const callback = mock(async () => {});
-
-      // Test with name and priority swapped (legacy support)
-      onShutdown(callback, 75, 'custom-name');
-
-      expect(getShutdownCallbackCount()).toBe(1);
-    });
-
-    it('should handle callback without any parameters', () => {
-      const callback = mock(async () => {});
-
-      onShutdown(callback);
-
-      expect(getShutdownCallbackCount()).toBe(1);
-    });
-
-    it('should validate setTimeout input', () => {
-      const shutdown = new Shutdown();
-
-      // Valid timeout
-      expect(() => shutdown.setTimeout(5000)).not.toThrow();
-
-      // Invalid timeouts should throw
-      expect(() => shutdown.setTimeout(-1)).toThrow();
-      expect(() => shutdown.setTimeout(0)).toThrow();
-      expect(() => shutdown.setTimeout(NaN)).toThrow();
-    });
-  });
-});
+});
\ No newline at end of file
diff --git a/libs/core/shutdown/test/shutdown-signals.test.ts b/libs/core/shutdown/test/shutdown-signals.test.ts
index a30bcc0..e5326a7 100644
--- a/libs/core/shutdown/test/shutdown-signals.test.ts
+++ b/libs/core/shutdown/test/shutdown-signals.test.ts
@@ -3,33 +3,30 @@ import { Shutdown } from '../src/shutdown';
 
 describe('Shutdown Signal Handlers', () => {
   let shutdown: Shutdown;
-  let processOnSpy: any;
+  let processOnceSpy: any;
   let processExitSpy: any;
-  const originalPlatform = Object.getOwnPropertyDescriptor(process, 'platform');
-  const originalOn = process.on;
+  const originalOnce = process.once;
   const originalExit = process.exit;
 
   beforeEach(() => {
     // Reset singleton instance
     (Shutdown as any).instance = null;
 
-    // Clean up global flag
-    delete (global as any).__SHUTDOWN_SIGNAL_RECEIVED__;
-
-    // Mock process.on
+    // Mock process.once to capture signal handlers
     const listeners: Record<string, Function[]> = {};
-    processOnSpy = mock((event: string, handler: Function) => {
+    processOnceSpy = mock((event: string, handler: Function) => {
       if (!listeners[event]) {
         listeners[event] = [];
       }
       listeners[event].push(handler);
+      return process;
     });
-    process.on = processOnSpy as any;
+    process.once = processOnceSpy as any;
 
     // Mock process.exit
     processExitSpy = mock((code?: number) => {
-      // Just record the call, don't throw
-      return;
+      // Just record the call, don't actually exit
+      return undefined as never;
     });
     process.exit = processExitSpy as any;
 
@@ -39,11 +36,8 @@ describe('Shutdown Signal Handlers', () => {
 
   afterEach(() => {
     // Restore original methods
-    process.on = originalOn;
+    process.once = originalOnce;
     process.exit = originalExit;
-    if (originalPlatform) {
-      Object.defineProperty(process, 'platform', originalPlatform);
-    }
 
     // Clean up
     (Shutdown as any).instance = null;
@@ -51,53 +45,29 @@ describe('Shutdown Signal Handlers', () => {
   });
 
   describe('Signal Handler Registration', () => {
-    it('should register Unix signal handlers on non-Windows', () => {
-      Object.defineProperty(process, 'platform', {
-        value: 'linux',
-        configurable: true,
-      });
-
+    it('should register signal handlers on initialization with autoRegister', () => {
       shutdown = new Shutdown({ autoRegister: true });
 
-      // Check that Unix signals were registered
-      expect(processOnSpy).toHaveBeenCalledWith('SIGTERM', expect.any(Function));
-      expect(processOnSpy).toHaveBeenCalledWith('SIGINT', expect.any(Function));
-      expect(processOnSpy).toHaveBeenCalledWith('SIGUSR2', expect.any(Function));
-      expect(processOnSpy).toHaveBeenCalledWith('uncaughtException', expect.any(Function));
-      expect(processOnSpy).toHaveBeenCalledWith('unhandledRejection', expect.any(Function));
-    });
-
-    it('should register Windows signal handlers on Windows', () => {
-      Object.defineProperty(process, 'platform', {
-        value: 'win32',
-        configurable: true,
-      });
-
-      shutdown = new Shutdown({ autoRegister: true });
-
-      // Check that Windows signals were registered
-      expect(processOnSpy).toHaveBeenCalledWith('SIGTERM', expect.any(Function));
-      expect(processOnSpy).toHaveBeenCalledWith('SIGINT', expect.any(Function));
-      expect(processOnSpy).not.toHaveBeenCalledWith('SIGUSR2', expect.any(Function));
-      expect(processOnSpy).toHaveBeenCalledWith('uncaughtException', expect.any(Function));
-      expect(processOnSpy).toHaveBeenCalledWith('unhandledRejection', expect.any(Function));
+      // Check that signals were registered
+      expect(processOnceSpy).toHaveBeenCalledWith('SIGTERM', expect.any(Function));
+      expect(processOnceSpy).toHaveBeenCalledWith('SIGINT', expect.any(Function));
     });
 
     it('should not register handlers when autoRegister is false', () => {
       shutdown = new Shutdown({ autoRegister: false });
 
-      expect(processOnSpy).not.toHaveBeenCalled();
+      expect(processOnceSpy).not.toHaveBeenCalled();
     });
 
     it('should not register handlers twice', () => {
       shutdown = new Shutdown({ autoRegister: true });
-      const callCount = processOnSpy.mock.calls.length;
+      const callCount = processOnceSpy.mock.calls.length;
 
       // Try to setup handlers again (internally)
       shutdown['setupSignalHandlers']();
 
       // Should not register additional handlers
-      expect(processOnSpy.mock.calls.length).toBe(callCount);
+      expect(processOnceSpy.mock.calls.length).toBe(callCount);
     });
   });
 
@@ -108,19 +78,19 @@ describe('Shutdown Signal Handlers', () => {
       shutdown.onShutdown(callback);
 
       const listeners = (global as any).__testListeners;
-      const sigtermHandler = listeners['SIGTERM'][0];
+      const sigtermHandler = listeners['SIGTERM']?.[0];
+      
+      expect(sigtermHandler).toBeDefined();
 
-      // Trigger SIGTERM (this starts async shutdown)
-      sigtermHandler();
+      // Mock the shutdown method to track it was called
+      const shutdownSpy = mock(shutdown.shutdown.bind(shutdown));
+      shutdown.shutdown = shutdownSpy;
 
-      // Verify flags are set immediately
-      expect(shutdown.isShutdownSignalReceived()).toBe(true);
-      expect((global as any).__SHUTDOWN_SIGNAL_RECEIVED__).toBe(true);
+      // Trigger SIGTERM
+      await sigtermHandler();
 
-      // Wait a bit for async shutdown to complete
-      await new Promise(resolve => setTimeout(resolve, 10));
-
-      // Now process.exit should have been called
+      // Verify shutdown was called
+      expect(shutdownSpy).toHaveBeenCalled();
       expect(processExitSpy).toHaveBeenCalledWith(0);
     });
 
@@ -130,125 +100,120 @@ describe('Shutdown Signal Handlers', () => {
       shutdown.onShutdown(callback);
 
       const listeners = (global as any).__testListeners;
-      const sigintHandler = listeners['SIGINT'][0];
+      const sigintHandler = listeners['SIGINT']?.[0];
+      
+      expect(sigintHandler).toBeDefined();
 
-      // Trigger SIGINT (this starts async shutdown)
-      sigintHandler();
+      // Mock the shutdown method
+      const shutdownSpy = mock(shutdown.shutdown.bind(shutdown));
+      shutdown.shutdown = shutdownSpy;
 
-      // Verify flags are set immediately
-      expect(shutdown.isShutdownSignalReceived()).toBe(true);
+      // Trigger SIGINT
+      await sigintHandler();
 
-      // Wait a bit for async shutdown to complete
-      await new Promise(resolve => setTimeout(resolve, 10));
-
-      // Now process.exit should have been called
+      // Verify shutdown was called
+      expect(shutdownSpy).toHaveBeenCalled();
       expect(processExitSpy).toHaveBeenCalledWith(0);
     });
 
-    it('should handle uncaughtException', async () => {
+    it('should exit with code 1 on shutdown error', async () => {
       shutdown = new Shutdown({ autoRegister: true });
 
-      const listeners = (global as any).__testListeners;
-      const exceptionHandler = listeners['uncaughtException'][0];
-
-      // Trigger uncaughtException (this starts async shutdown with exit code 1)
-      exceptionHandler(new Error('Uncaught error'));
-
-      // Wait a bit for async shutdown to complete
-      await new Promise(resolve => setTimeout(resolve, 10));
-
-      // Should exit with code 1 for uncaught exceptions
-      expect(processExitSpy).toHaveBeenCalledWith(1);
-    });
-
-    it('should handle unhandledRejection', async () => {
-      shutdown = new Shutdown({ autoRegister: true });
+      // Make shutdown throw an error
+      shutdown.shutdown = mock(async () => {
+        throw new Error('Shutdown failed');
+      });
 
       const listeners = (global as any).__testListeners;
-      const rejectionHandler = listeners['unhandledRejection'][0];
+      const sigtermHandler = listeners['SIGTERM']?.[0];
 
-      // Trigger unhandledRejection (this starts async shutdown with exit code 1)
-      rejectionHandler(new Error('Unhandled rejection'));
+      // Trigger SIGTERM
+      await sigtermHandler();
 
-      // Wait a bit for async shutdown to complete
-      await new Promise(resolve => setTimeout(resolve, 10));
-
-      // Should exit with code 1 for unhandled rejections
+      // Should exit with code 1 on error
       expect(processExitSpy).toHaveBeenCalledWith(1);
     });
 
     it('should not process signal if already shutting down', async () => {
       shutdown = new Shutdown({ autoRegister: true });
 
-      // Start shutdown
+      // Set shutting down flag
       shutdown['isShuttingDown'] = true;
 
       const listeners = (global as any).__testListeners;
-      const sigtermHandler = listeners['SIGTERM'][0];
+      const sigtermHandler = listeners['SIGTERM']?.[0];
 
-      // Mock shutdownAndExit to track calls
-      const shutdownAndExitSpy = mock(() => Promise.resolve());
-      shutdown.shutdownAndExit = shutdownAndExitSpy as any;
+      // Mock shutdown to ensure it's not called
+      const shutdownSpy = mock(shutdown.shutdown.bind(shutdown));
+      shutdown.shutdown = shutdownSpy;
 
       // Trigger SIGTERM
-      sigtermHandler();
+      await sigtermHandler();
 
-      // Should not call shutdownAndExit since already shutting down
-      expect(shutdownAndExitSpy).not.toHaveBeenCalled();
-    });
-
-    it('should handle shutdown failure in signal handler', async () => {
-      shutdown = new Shutdown({ autoRegister: true });
-
-      // Mock shutdownAndExit to reject
-      shutdown.shutdownAndExit = mock(async () => {
-        throw new Error('Shutdown failed');
-      }) as any;
-
-      const listeners = (global as any).__testListeners;
-      const sigtermHandler = listeners['SIGTERM'][0];
-
-      // Trigger SIGTERM - should fall back to process.exit(1)
-      sigtermHandler();
-
-      // Wait a bit for async shutdown to fail and fallback to occur
-      await new Promise(resolve => setTimeout(resolve, 10));
-
-      expect(processExitSpy).toHaveBeenCalledWith(1);
+      // Should not call shutdown or exit
+      expect(shutdownSpy).not.toHaveBeenCalled();
+      expect(processExitSpy).not.toHaveBeenCalled();
     });
   });
 
-  describe('Global Flag Behavior', () => {
-    it('should set global shutdown flag on signal', async () => {
-      delete (global as any).__SHUTDOWN_SIGNAL_RECEIVED__;
+  describe('Singleton Behavior with Signals', () => {
+    it('should use singleton instance for signal handling', () => {
+      const instance1 = Shutdown.getInstance();
+      const instance2 = Shutdown.getInstance();
 
+      expect(instance1).toBe(instance2);
+      
+      // Only one set of signal handlers should be registered
+      expect(processOnceSpy).toHaveBeenCalledTimes(2); // SIGTERM and SIGINT
+    });
+
+    it('should handle callbacks registered before signal', async () => {
+      shutdown = new Shutdown({ autoRegister: true });
+      
+      const callback1 = mock(async () => {});
+      const callback2 = mock(async () => {});
+      
+      shutdown.onShutdown(callback1, 10);
+      shutdown.onShutdown(callback2, 20);
+
+      const listeners = (global as any).__testListeners;
+      const sigtermHandler = listeners['SIGTERM']?.[0];
+
+      // Replace shutdown method to test callback execution
+      const originalShutdown = shutdown.shutdown.bind(shutdown);
+      let shutdownCalled = false;
+      shutdown.shutdown = mock(async () => {
+        shutdownCalled = true;
+        await originalShutdown();
+      });
+
+      // Trigger signal
+      await sigtermHandler();
+
+      expect(shutdownCalled).toBe(true);
+      expect(processExitSpy).toHaveBeenCalledWith(0);
+    });
+  });
+
+  describe('Edge Cases', () => {
+    it('should handle missing signal handler gracefully', () => {
       shutdown = new Shutdown({ autoRegister: true });
 
       const listeners = (global as any).__testListeners;
-      const sigtermHandler = listeners['SIGTERM'][0];
-
-      // Trigger signal (this sets the flag immediately)
-      sigtermHandler();
-
-      expect((global as any).__SHUTDOWN_SIGNAL_RECEIVED__).toBe(true);
-
-      // Wait for async shutdown to complete to avoid hanging promises
-      await new Promise(resolve => setTimeout(resolve, 10));
+      
+      // Verify handlers exist
+      expect(listeners['SIGTERM']).toBeDefined();
+      expect(listeners['SIGINT']).toBeDefined();
+      expect(listeners['SIGTERM'].length).toBeGreaterThan(0);
+      expect(listeners['SIGINT'].length).toBeGreaterThan(0);
     });
 
-    it('should check global flag in isShutdownSignalReceived', () => {
-      shutdown = new Shutdown({ autoRegister: false });
+    it('should work with default options', () => {
+      // Create with defaults
+      shutdown = new Shutdown();
 
-      expect(shutdown.isShutdownSignalReceived()).toBe(false);
-
-      // Set global flag
-      (global as any).__SHUTDOWN_SIGNAL_RECEIVED__ = true;
-
-      // Even without instance flag, should return true
-      expect(shutdown.isShutdownSignalReceived()).toBe(true);
-
-      // Clean up
-      delete (global as any).__SHUTDOWN_SIGNAL_RECEIVED__;
+      // Should auto-register by default
+      expect(processOnceSpy).toHaveBeenCalled();
     });
   });
-});
+});
\ No newline at end of file
diff --git a/libs/core/shutdown/test/shutdown.test.ts b/libs/core/shutdown/test/shutdown.test.ts
index ca8630c..6e4e596 100644
--- a/libs/core/shutdown/test/shutdown.test.ts
+++ b/libs/core/shutdown/test/shutdown.test.ts
@@ -33,7 +33,7 @@ describe('Shutdown', () => {
     it('should register high priority handler', () => {
       const handler = mock(async () => {});
 
-      shutdown.onShutdownHigh(handler, 'High Priority Task');
+      shutdown.onShutdown(handler, 10, 'High Priority Task');
 
       expect(shutdown['callbacks']).toHaveLength(1);
       expect(shutdown['callbacks'][0].name).toBe('High Priority Task');
@@ -43,7 +43,7 @@ describe('Shutdown', () => {
     it('should register medium priority handler', () => {
       const handler = mock(async () => {});
 
-      shutdown.onShutdownMedium(handler, 'Medium Priority Task');
+      shutdown.onShutdown(handler, 50, 'Medium Priority Task');
 
       expect(shutdown['callbacks']).toHaveLength(1);
       expect(shutdown['callbacks'][0].priority).toBe(50);
@@ -52,7 +52,7 @@ describe('Shutdown', () => {
     it('should register low priority handler', () => {
       const handler = mock(async () => {});
 
-      shutdown.onShutdownLow(handler, 'Low Priority Task');
+      shutdown.onShutdown(handler, 90, 'Low Priority Task');
 
       expect(shutdown['callbacks']).toHaveLength(1);
       expect(shutdown['callbacks'][0].priority).toBe(90);
@@ -63,9 +63,9 @@ describe('Shutdown', () => {
       const handler2 = mock(async () => {});
       const handler3 = mock(async () => {});
 
-      shutdown.onShutdownHigh(handler1, 'First');
-      shutdown.onShutdownHigh(handler2, 'Second');
-      shutdown.onShutdownHigh(handler3, 'Third');
+      shutdown.onShutdown(handler1, 10, 'First');
+      shutdown.onShutdown(handler2, 10, 'Second');
+      shutdown.onShutdown(handler3, 10, 'Third');
 
       expect(shutdown['callbacks']).toHaveLength(3);
       expect(shutdown['callbacks'][0].name).toBe('First');
@@ -89,9 +89,9 @@ describe('Shutdown', () => {
         executionOrder.push('low');
       });
 
-      shutdown.onShutdownLow(lowHandler, 'Low');
-      shutdown.onShutdownMedium(mediumHandler, 'Medium');
-      shutdown.onShutdownHigh(highHandler, 'High');
+      shutdown.onShutdown(lowHandler, 90, 'Low');
+      shutdown.onShutdown(mediumHandler, 50, 'Medium');
+      shutdown.onShutdown(highHandler, 10, 'High');
 
       await shutdown.shutdown();
 
@@ -100,7 +100,7 @@ describe('Shutdown', () => {
 
     it('should only shutdown once', async () => {
       const handler = mock(async () => {});
-      shutdown.onShutdownHigh(handler, 'Handler');
+      shutdown.onShutdown(handler, 10, 'Handler');
 
       await shutdown.shutdown();
       await shutdown.shutdown(); // Second call should be ignored
@@ -115,8 +115,8 @@ describe('Shutdown', () => {
 
       const successHandler = mock(async () => {});
 
-      shutdown.onShutdownHigh(errorHandler, 'Error Handler');
-      shutdown.onShutdownHigh(successHandler, 'Success Handler');
+      shutdown.onShutdown(errorHandler, 10, 'Error Handler');
+      shutdown.onShutdown(successHandler, 10, 'Success Handler');
 
       await shutdown.shutdown();
 
@@ -130,10 +130,10 @@ describe('Shutdown', () => {
       });
 
       shutdown = Shutdown.getInstance({ timeout: 100 });
-      shutdown.onShutdownHigh(slowHandler, 'Slow Handler');
+      shutdown.onShutdown(slowHandler, 10, 'Slow Handler');
 
       const start = Date.now();
-      await shutdown.shutdown();
+      await expect(shutdown.shutdown()).rejects.toThrow('Shutdown timeout');
       const duration = Date.now() - start;
 
       // Shutdown waits for timeout (100ms) plus some processing time
@@ -144,9 +144,9 @@ describe('Shutdown', () => {
 
   describe('reset', () => {
     it('should clear all handlers', () => {
-      shutdown.onShutdownHigh(async () => {}, 'Handler 1');
-      shutdown.onShutdownMedium(async () => {}, 'Handler 2');
-      shutdown.onShutdownLow(async () => {}, 'Handler 3');
+      shutdown.onShutdown(async () => {}, 10, 'Handler 1');
+      shutdown.onShutdown(async () => {}, 50, 'Handler 2');
+      shutdown.onShutdown(async () => {}, 90, 'Handler 3');
 
       // Manually clear callbacks to simulate reset
       shutdown['callbacks'] = [];
@@ -157,14 +157,14 @@ describe('Shutdown', () => {
     it('should reset shutdown state', async () => {
       const handler = mock(async () => {});
 
-      shutdown.onShutdownHigh(handler, 'Handler');
+      shutdown.onShutdown(handler, 10, 'Handler');
       await shutdown.shutdown();
 
       // Reset by creating new instance
       (Shutdown as any).instance = null;
       shutdown = Shutdown.getInstance({ timeout: 1000 });
 
-      shutdown.onShutdownHigh(handler, 'Handler');
+      shutdown.onShutdown(handler, 10, 'Handler');
       await shutdown.shutdown();
 
       expect(handler).toHaveBeenCalledTimes(2);