feat(03-02): instrument processJob with fire-and-forget analytics events

- Add import for recordProcessingEvent from analyticsService
- Emit upload_started after markAsProcessing (job processing start)
- Emit completed with duration_ms after markAsCompleted (job success)
- Emit failed with duration_ms and error_message in catch block (job failure)
- All calls are void/fire-and-forget (no await) per PITFALL-6 constraint
- Null-guard on job in catch block prevents runtime errors

backend/src/services/jobProcessorService.ts

@@ -3,6 +3,7 @@ import { ProcessingJobModel, ProcessingJob } from '../models/ProcessingJobModel'
 import { DocumentModel } from '../models/DocumentModel';
 import { fileStorageService } from './fileStorageService';
 import { unifiedDocumentProcessor } from './unifiedDocumentProcessor';
+import { recordProcessingEvent } from './analyticsService';
 
 export class JobProcessorService {
   private isProcessing = false;
@@ -133,6 +134,13 @@ export class JobProcessorService {
       await ProcessingJobModel.markAsProcessing(jobId);
       jobStatusUpdated = true; // Track that we've updated status
 
+      // Analytics: job processing started (fire-and-forget, void return)
+      recordProcessingEvent({
+        document_id: job.document_id,
+        user_id: job.user_id,
+        event_type: 'upload_started',
+      });
+
       // Add timeout protection (28 minutes for API immediate processing, 14 for scheduled function)
       // API endpoint has 30-min Cloud Run timeout; scheduled function has 15 min
       const processingTimeout = 28 * 60 * 1000; // 28 minutes in milliseconds
@@ -333,6 +341,14 @@ export class JobProcessorService {
             processingTime,
             attempts: job.attempts + 1,
           });
+
+          // Analytics: job completed (fire-and-forget, void return)
+          recordProcessingEvent({
+            document_id: job.document_id,
+            user_id: job.user_id,
+            event_type: 'completed',
+            duration_ms: processingTime,
+          });
         })(),
         timeoutPromise
       ]);
@@ -363,6 +379,18 @@ export class JobProcessorService {
         attempts: job ? job.attempts + 1 : 'unknown',
       });
 
+      // Analytics: job failed (fire-and-forget, void return)
+      // Guard with job check — job is null if findById failed before assignment
+      if (job) {
+        recordProcessingEvent({
+          document_id: job.document_id,
+          user_id: job.user_id,
+          event_type: 'failed',
+          duration_ms: processingTime,
+          error_message: errorMessage,
+        });
+      }
+
       // Mark job as failed (will auto-retry if attempts < max_attempts)
       try {
         await ProcessingJobModel.markAsFailed(jobId, errorMessage);