feat: Implement Worker Service v2 with improved architecture

- Complete rewrite of the Worker Service following object-oriented principles.
- Introduced a single long-lived database connection to reduce overhead.
- Implemented event-driven queues to eliminate polling.
- Added DRY utilities for pagination and settings management.
- Reduced code size significantly from 1173 lines to approximately 600-700 lines.
- Created various composed services including DatabaseManager, SessionManager, and SDKAgent.
- Enhanced SSE broadcasting capabilities for real-time client updates.
- Established a structured approach for session lifecycle management and event handling.
- Introduced type safety with shared TypeScript interfaces for better maintainability.

src/services/worker/DatabaseManager.ts

@@ -0,0 +1,115 @@
+/**
+ * DatabaseManager: Single long-lived database connection
+ *
+ * Responsibility:
+ * - Manage single database connection for worker lifetime
+ * - Provide centralized access to SessionStore and SessionSearch
+ * - High-level database operations
+ * - ChromaSync integration
+ */
+
+import { SessionStore } from '../sqlite/SessionStore.js';
+import { SessionSearch } from '../sqlite/SessionSearch.js';
+import { ChromaSync } from '../sync/ChromaSync.js';
+import { logger } from '../../utils/logger.js';
+import type { DBSession } from '../worker-types.js';
+
+export class DatabaseManager {
+  private sessionStore: SessionStore | null = null;
+  private sessionSearch: SessionSearch | null = null;
+  private chromaSync: ChromaSync | null = null;
+
+  /**
+   * Initialize database connection (once, stays open)
+   */
+  async initialize(): Promise<void> {
+    // Open database connection (ONCE)
+    this.sessionStore = new SessionStore();
+    this.sessionSearch = new SessionSearch();
+
+    // Initialize ChromaSync
+    this.chromaSync = new ChromaSync('claude-mem');
+
+    // Start background backfill (fire-and-forget)
+    this.chromaSync.ensureBackfilled().catch(() => {});
+
+    logger.info('DB', 'Database initialized');
+  }
+
+  /**
+   * Close database connection
+   */
+  async close(): Promise<void> {
+    if (this.sessionStore) {
+      this.sessionStore.close();
+      this.sessionStore = null;
+    }
+    if (this.sessionSearch) {
+      this.sessionSearch.close();
+      this.sessionSearch = null;
+    }
+    logger.info('DB', 'Database closed');
+  }
+
+  /**
+   * Get SessionStore instance (throws if not initialized)
+   */
+  getSessionStore(): SessionStore {
+    if (!this.sessionStore) {
+      throw new Error('Database not initialized');
+    }
+    return this.sessionStore;
+  }
+
+  /**
+   * Get SessionSearch instance (throws if not initialized)
+   */
+  getSessionSearch(): SessionSearch {
+    if (!this.sessionSearch) {
+      throw new Error('Database not initialized');
+    }
+    return this.sessionSearch;
+  }
+
+  /**
+   * Get ChromaSync instance (throws if not initialized)
+   */
+  getChromaSync(): ChromaSync {
+    if (!this.chromaSync) {
+      throw new Error('ChromaSync not initialized');
+    }
+    return this.chromaSync;
+  }
+
+  /**
+   * Cleanup orphaned sessions from previous runs
+   * @returns Number of sessions cleaned
+   */
+  cleanupOrphanedSessions(): number {
+    return this.getSessionStore().cleanupOrphanedSessions();
+  }
+
+  /**
+   * Get session by ID (throws if not found)
+   */
+  getSessionById(sessionDbId: number): {
+    id: number;
+    claude_session_id: string;
+    sdk_session_id: string | null;
+    project: string;
+    user_prompt: string;
+  } {
+    const session = this.getSessionStore().getSessionById(sessionDbId);
+    if (!session) {
+      throw new Error(`Session ${sessionDbId} not found`);
+    }
+    return session;
+  }
+
+  /**
+   * Mark session as completed
+   */
+  markSessionComplete(sessionDbId: number): void {
+    this.getSessionStore().markSessionCompleted(sessionDbId);
+  }
+}