feat: Introduce SessionEventBroadcaster and SessionCompletionHandler for improved session management

- Added SessionEventBroadcaster to handle broadcasting of session lifecycle events, consolidating SSE broadcasting and processing status updates.
- Refactored SessionRoutes to utilize SessionEventBroadcaster for broadcasting events related to new prompts, session starts, and completions.
- Created SessionCompletionHandler to centralize session completion logic, reducing duplication across multiple endpoints.
- Updated WorkerService to initialize SessionEventBroadcaster and pass it to SessionRoutes.

src/services/worker/session/SessionCompletionHandler.ts

@@ -0,0 +1,62 @@
+/**
+ * Session Completion Handler
+ *
+ * Consolidates session completion logic to eliminate duplication across
+ * three different completion endpoints (DELETE, POST by DB ID, POST by Claude ID).
+ *
+ * All completion flows follow the same pattern:
+ * 1. Delete session from SessionManager (aborts SDK agent)
+ * 2. Mark session complete in database
+ * 3. Broadcast session completed event
+ */
+
+import { SessionManager } from '../SessionManager.js';
+import { DatabaseManager } from '../DatabaseManager.js';
+import { SessionEventBroadcaster } from '../events/SessionEventBroadcaster.js';
+
+export class SessionCompletionHandler {
+  constructor(
+    private sessionManager: SessionManager,
+    private dbManager: DatabaseManager,
+    private eventBroadcaster: SessionEventBroadcaster
+  ) {}
+
+  /**
+   * Complete session by database ID
+   * Used by DELETE /api/sessions/:id and POST /api/sessions/:id/complete
+   */
+  async completeByDbId(sessionDbId: number): Promise<void> {
+    // Delete from session manager (aborts SDK agent)
+    await this.sessionManager.deleteSession(sessionDbId);
+
+    // Mark session complete in database
+    this.dbManager.markSessionComplete(sessionDbId);
+
+    // Broadcast session completed event
+    this.eventBroadcaster.broadcastSessionCompleted(sessionDbId);
+  }
+
+  /**
+   * Complete session by Claude session ID
+   * Used by POST /api/sessions/complete (cleanup-hook endpoint)
+   *
+   * @returns true if session was found and completed, false if no active session found
+   */
+  async completeByClaudeId(claudeSessionId: string): Promise<boolean> {
+    const store = this.dbManager.getSessionStore();
+
+    // Find session by claudeSessionId
+    const session = store.findActiveSDKSession(claudeSessionId);
+    if (!session) {
+      // No active session - nothing to clean up (may have already been completed)
+      return false;
+    }
+
+    const sessionDbId = session.id;
+
+    // Complete using standard flow
+    await this.completeByDbId(sessionDbId);
+
+    return true;
+  }
+}