fix: critical memory leak from per-session database connections (#554)

* fix: critical memory leak from per-session database connections (#542)

Each MCP session was creating its own database connection (~900MB),
causing OOM kills every ~20 minutes with 3-4 concurrent sessions.

Changes:
- Add SharedDatabase singleton pattern - all sessions share ONE connection
- Reduce session timeout from 30 min to 5 min (configurable)
- Add eager cleanup for reconnecting instances
- Fix telemetry event listener leak

Memory impact: ~900MB/session → ~68MB shared + ~5MB/session overhead

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Conceived by Romuald Czlonkowski - https://www.aiadvisors.pl/en

* fix: resolve test failures from shared database race conditions

- Fix `shutdown()` to respect shared database pattern (was directly closing)
- Add `await this.initialized` in both `close()` and `shutdown()` to prevent
  race condition where cleanup runs while initialization is in progress
- Add double-shutdown protection with `isShutdown` flag
- Export `SharedDatabaseState` type for proper typing
- Include error details in debug logs
- Add MCP server close to `shutdown()` for consistency with `close()`
- Null out `earlyLogger` in `shutdown()` for consistency

The CI test failure "The database connection is not open" was caused by:
1. `shutdown()` directly calling `this.db.close()` which closed the SHARED
   database connection, breaking subsequent tests
2. Race condition where `shutdown()` ran before initialization completed

Conceived by Romuald Członkowski - www.aiadvisors.pl/en

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* test: add unit tests for shared-database module

Add comprehensive unit tests covering:
- getSharedDatabase: initialization, reuse, different path error, concurrent requests
- releaseSharedDatabase: refCount decrement, double-release guard
- closeSharedDatabase: state clearing, error handling, re-initialization
- Helper functions: isSharedDatabaseInitialized, getSharedDatabaseRefCount

21 tests covering the singleton database connection pattern used to prevent
~900MB memory leaks per session.

Conceived by Romuald Członkowski - www.aiadvisors.pl/en

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

tests/unit/database/shared-database.test.ts

@@ -0,0 +1,302 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+
+// Mock dependencies at module level
+const mockDb = {
+  prepare: vi.fn().mockReturnValue({
+    get: vi.fn(),
+    all: vi.fn(),
+    run: vi.fn()
+  }),
+  exec: vi.fn(),
+  close: vi.fn(),
+  pragma: vi.fn(),
+  inTransaction: false,
+  transaction: vi.fn(),
+  checkFTS5Support: vi.fn()
+};
+
+vi.mock('../../../src/database/database-adapter', () => ({
+  createDatabaseAdapter: vi.fn().mockResolvedValue(mockDb)
+}));
+
+vi.mock('../../../src/database/node-repository', () => ({
+  NodeRepository: vi.fn().mockImplementation(() => ({
+    getNodeTypes: vi.fn().mockReturnValue([])
+  }))
+}));
+
+vi.mock('../../../src/templates/template-service', () => ({
+  TemplateService: vi.fn().mockImplementation(() => ({}))
+}));
+
+vi.mock('../../../src/services/enhanced-config-validator', () => ({
+  EnhancedConfigValidator: {
+    initializeSimilarityServices: vi.fn()
+  }
+}));
+
+vi.mock('../../../src/utils/logger', () => ({
+  logger: {
+    debug: vi.fn(),
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn()
+  }
+}));
+
+describe('Shared Database Module', () => {
+  let sharedDbModule: typeof import('../../../src/database/shared-database');
+  let createDatabaseAdapter: ReturnType<typeof vi.fn>;
+
+  beforeEach(async () => {
+    // Reset all mocks
+    vi.clearAllMocks();
+    mockDb.close.mockReset();
+
+    // Reset modules to get fresh state
+    vi.resetModules();
+
+    // Import fresh module
+    sharedDbModule = await import('../../../src/database/shared-database');
+
+    // Get the mocked function
+    const adapterModule = await import('../../../src/database/database-adapter');
+    createDatabaseAdapter = adapterModule.createDatabaseAdapter as ReturnType<typeof vi.fn>;
+  });
+
+  afterEach(async () => {
+    // Clean up any shared state by closing
+    try {
+      await sharedDbModule.closeSharedDatabase();
+    } catch {
+      // Ignore errors during cleanup
+    }
+  });
+
+  describe('getSharedDatabase', () => {
+    it('should initialize database on first call', async () => {
+      const state = await sharedDbModule.getSharedDatabase('/path/to/db');
+
+      expect(state).toBeDefined();
+      expect(state.db).toBe(mockDb);
+      expect(state.dbPath).toBe('/path/to/db');
+      expect(state.refCount).toBe(1);
+      expect(state.initialized).toBe(true);
+      expect(createDatabaseAdapter).toHaveBeenCalledWith('/path/to/db');
+    });
+
+    it('should reuse existing connection and increment refCount', async () => {
+      // First call initializes
+      const state1 = await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(state1.refCount).toBe(1);
+
+      // Second call reuses
+      const state2 = await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(state2.refCount).toBe(2);
+
+      // Same object
+      expect(state1).toBe(state2);
+
+      // Only initialized once
+      expect(createDatabaseAdapter).toHaveBeenCalledTimes(1);
+    });
+
+    it('should throw error when called with different path', async () => {
+      await sharedDbModule.getSharedDatabase('/path/to/db1');
+
+      await expect(sharedDbModule.getSharedDatabase('/path/to/db2'))
+        .rejects.toThrow('Shared database already initialized with different path');
+    });
+
+    it('should handle concurrent initialization requests', async () => {
+      // Start two requests concurrently
+      const [state1, state2] = await Promise.all([
+        sharedDbModule.getSharedDatabase('/path/to/db'),
+        sharedDbModule.getSharedDatabase('/path/to/db')
+      ]);
+
+      // Both should get the same state
+      expect(state1).toBe(state2);
+
+      // RefCount should be 2 (one for each call)
+      expect(state1.refCount).toBe(2);
+
+      // Only one actual initialization
+      expect(createDatabaseAdapter).toHaveBeenCalledTimes(1);
+    });
+
+    it('should handle initialization failure', async () => {
+      createDatabaseAdapter.mockRejectedValueOnce(new Error('DB error'));
+
+      await expect(sharedDbModule.getSharedDatabase('/path/to/db'))
+        .rejects.toThrow('DB error');
+
+      // After failure, should not be initialized
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(false);
+    });
+
+    it('should allow retry after initialization failure', async () => {
+      // First call fails
+      createDatabaseAdapter.mockRejectedValueOnce(new Error('DB error'));
+      await expect(sharedDbModule.getSharedDatabase('/path/to/db'))
+        .rejects.toThrow('DB error');
+
+      // Reset mock for successful call
+      createDatabaseAdapter.mockResolvedValueOnce(mockDb);
+
+      // Second call succeeds
+      const state = await sharedDbModule.getSharedDatabase('/path/to/db');
+
+      expect(state).toBeDefined();
+      expect(state.initialized).toBe(true);
+    });
+  });
+
+  describe('releaseSharedDatabase', () => {
+    it('should decrement refCount', async () => {
+      const state = await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(state.refCount).toBe(1);
+
+      sharedDbModule.releaseSharedDatabase(state);
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(0);
+    });
+
+    it('should not decrement below 0', async () => {
+      const state = await sharedDbModule.getSharedDatabase('/path/to/db');
+
+      // Release once (refCount: 1 -> 0)
+      sharedDbModule.releaseSharedDatabase(state);
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(0);
+
+      // Release again (should stay at 0, not go negative)
+      sharedDbModule.releaseSharedDatabase(state);
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(0);
+    });
+
+    it('should handle null state gracefully', () => {
+      // Should not throw
+      sharedDbModule.releaseSharedDatabase(null as any);
+    });
+
+    it('should not close database when refCount hits 0', async () => {
+      const state = await sharedDbModule.getSharedDatabase('/path/to/db');
+      sharedDbModule.releaseSharedDatabase(state);
+
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(0);
+      expect(mockDb.close).not.toHaveBeenCalled();
+
+      // Database should still be accessible
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(true);
+    });
+  });
+
+  describe('closeSharedDatabase', () => {
+    it('should close database and clear state', async () => {
+      // Get state
+      await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(true);
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(1);
+
+      await sharedDbModule.closeSharedDatabase();
+
+      // State should be cleared
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(false);
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(0);
+    });
+
+    it('should handle close error gracefully', async () => {
+      await sharedDbModule.getSharedDatabase('/path/to/db');
+      mockDb.close.mockImplementationOnce(() => {
+        throw new Error('Close error');
+      });
+
+      // Should not throw
+      await sharedDbModule.closeSharedDatabase();
+
+      // State should still be cleared
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(false);
+    });
+
+    it('should be idempotent when already closed', async () => {
+      // Close without ever initializing
+      await sharedDbModule.closeSharedDatabase();
+
+      // Should not throw
+      await sharedDbModule.closeSharedDatabase();
+    });
+
+    it('should allow re-initialization after close', async () => {
+      // Initialize
+      const state1 = await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(state1.refCount).toBe(1);
+
+      // Close
+      await sharedDbModule.closeSharedDatabase();
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(false);
+
+      // Re-initialize
+      const state2 = await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(state2.refCount).toBe(1);
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(true);
+
+      // Should be a new state object
+      expect(state1).not.toBe(state2);
+    });
+  });
+
+  describe('isSharedDatabaseInitialized', () => {
+    it('should return false before initialization', () => {
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(false);
+    });
+
+    it('should return true after initialization', async () => {
+      await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(true);
+    });
+
+    it('should return false after close', async () => {
+      await sharedDbModule.getSharedDatabase('/path/to/db');
+      await sharedDbModule.closeSharedDatabase();
+      expect(sharedDbModule.isSharedDatabaseInitialized()).toBe(false);
+    });
+  });
+
+  describe('getSharedDatabaseRefCount', () => {
+    it('should return 0 before initialization', () => {
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(0);
+    });
+
+    it('should return correct refCount after multiple operations', async () => {
+      const state = await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(1);
+
+      await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(2);
+
+      await sharedDbModule.getSharedDatabase('/path/to/db');
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(3);
+
+      sharedDbModule.releaseSharedDatabase(state);
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(2);
+    });
+
+    it('should return 0 after close', async () => {
+      await sharedDbModule.getSharedDatabase('/path/to/db');
+      await sharedDbModule.closeSharedDatabase();
+      expect(sharedDbModule.getSharedDatabaseRefCount()).toBe(0);
+    });
+  });
+
+  describe('SharedDatabaseState interface', () => {
+    it('should expose correct properties', async () => {
+      const state = await sharedDbModule.getSharedDatabase('/path/to/db');
+
+      expect(state).toHaveProperty('db');
+      expect(state).toHaveProperty('repository');
+      expect(state).toHaveProperty('templateService');
+      expect(state).toHaveProperty('dbPath');
+      expect(state).toHaveProperty('refCount');
+      expect(state).toHaveProperty('initialized');
+    });
+  });
+});

tests/unit/http-server-session-management.test.ts

@@ -333,13 +333,14 @@ describe('HTTP Server Session Management', () => {
       server = new SingleSessionHTTPServer();
       
       // Mock expired sessions
+      // Note: Default session timeout is 5 minutes (configurable via SESSION_TIMEOUT_MINUTES)
       const mockSessionMetadata = {
-        'session-1': { 
-          lastAccess: new Date(Date.now() - 40 * 60 * 1000), // 40 minutes ago (expired)
+        'session-1': {
+          lastAccess: new Date(Date.now() - 10 * 60 * 1000), // 10 minutes ago (expired with 5 min timeout)
           createdAt: new Date(Date.now() - 60 * 60 * 1000)
         },
-        'session-2': { 
-          lastAccess: new Date(Date.now() - 10 * 60 * 1000), // 10 minutes ago (not expired)
+        'session-2': {
+          lastAccess: new Date(Date.now() - 2 * 60 * 1000), // 2 minutes ago (not expired with 5 min timeout)
           createdAt: new Date(Date.now() - 20 * 60 * 1000)
         }
       };
@@ -514,15 +515,16 @@ describe('HTTP Server Session Management', () => {
 
     it('should get session metrics correctly', async () => {
       server = new SingleSessionHTTPServer();
-      
+
+      // Note: Default session timeout is 5 minutes (configurable via SESSION_TIMEOUT_MINUTES)
       const now = Date.now();
       (server as any).sessionMetadata = {
         'active-session': {
-          lastAccess: new Date(now - 10 * 60 * 1000), // 10 minutes ago
+          lastAccess: new Date(now - 2 * 60 * 1000), // 2 minutes ago (not expired with 5 min timeout)
           createdAt: new Date(now - 20 * 60 * 1000)
         },
         'expired-session': {
-          lastAccess: new Date(now - 40 * 60 * 1000), // 40 minutes ago (expired)
+          lastAccess: new Date(now - 10 * 60 * 1000), // 10 minutes ago (expired with 5 min timeout)
           createdAt: new Date(now - 60 * 60 * 1000)
         }
       };
@@ -532,7 +534,7 @@ describe('HTTP Server Session Management', () => {
       };
 
       const metrics = (server as any).getSessionMetrics();
-      
+
       expect(metrics.totalSessions).toBe(2);
       expect(metrics.activeSessions).toBe(2);
       expect(metrics.expiredSessions).toBe(1);