fix: regenerate SN archive with task-specific DOCX headers

Invalidate cached monthly service-task ZIP archives so exports are rebuilt with the latest task/work-order/vehicle header data. Keep stale detection for work-order archives and add regression tests for per-task header isolation and stale cache replacement.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/modules/fleet/tests/test_work_order_images_endpoint.py

@@ -1,4 +1,5 @@
 from django.contrib.auth import get_user_model
+from django.core.files.base import ContentFile
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.test import TestCase
 from django.urls import reverse
@@ -352,6 +353,58 @@ class WorkOrderImagesEndpointTests(TestCase):
         self.assertNotIn('MT250226', header_xml)
         self.assertNotIn('LTM-1350', header_xml)
 
+    def test_monthly_service_tasks_archive_uses_task_specific_headers_for_each_docx(self):
+        vehicle_two = Vehicle.objects.create(
+            asset_type='crane',
+            registration_number='WO-IMG-002',
+            make='Tadano',
+            model='ATF 90',
+            crane_serial_number='SN-999',
+            superstructure_working_hours=444,
+            chassis_working_hours=555,
+            current_mileage=66677,
+        )
+        work_order_two = WorkOrder.objects.create(
+            vehicle=vehicle_two,
+            creator=self.user,
+            display_code='MT160726',
+            purpose='kontrola',
+        )
+        Task.objects.create(
+            title='Drugi zadatak',
+            assigned_to=self.user,
+            vehicle=vehicle_two,
+            work_order=work_order_two,
+            scheduled_date=date(2033, 12, 26),
+            service_report_note='Napomena drugog taska',
+        )
+
+        response = self.client.get('/api/fleet/reports/monthly-service-tasks-archive/?year=2033&month=12')
+        self.assertEqual(response.status_code, 200, response.content)
+
+        archive = zipfile.ZipFile(BytesIO(response.content))
+        first_docx = 'MT150726.SN-Test_servisni_zadatak.docx'
+        second_docx = 'MT160726.SN-Drugi_zadatak.docx'
+        self.assertIn(first_docx, archive.namelist())
+        self.assertIn(second_docx, archive.namelist())
+
+        first_header = zipfile.ZipFile(BytesIO(archive.read(first_docx))).read('word/header1.xml').decode('utf-8', errors='ignore')
+        second_header = zipfile.ZipFile(BytesIO(archive.read(second_docx))).read('word/header1.xml').decode('utf-8', errors='ignore')
+
+        self.assertIn('Liebherr LTM 1090', first_header)
+        self.assertIn('MT150726', first_header)
+        self.assertNotIn('Tadano ATF 90', first_header)
+        self.assertNotIn('MT160726', first_header)
+
+        self.assertIn('Tadano ATF 90', second_header)
+        self.assertIn('SN-999', second_header)
+        self.assertIn('444', second_header)
+        self.assertIn('555', second_header)
+        self.assertIn('66677', second_header)
+        self.assertIn('MT160726', second_header)
+        self.assertNotIn('Liebherr LTM 1090', second_header)
+        self.assertNotIn('MT150726', second_header)
+
     def test_monthly_work_orders_archive_contains_work_orders_and_invoices_folder(self):
         WorkOrderInvoice.objects.create(
             work_order=self.work_order,
@@ -402,6 +455,36 @@ class WorkOrderImagesEndpointTests(TestCase):
         self.assertTrue(notifications.filter(metadata__entity_type='fleet_archive', metadata__stage='requested').exists())
         self.assertTrue(notifications.filter(metadata__entity_type='fleet_archive', metadata__stage='completed').exists())
 
+    def test_monthly_service_tasks_archive_request_ignores_stale_cached_archive(self):
+        stale = GeneratedFleetArchive.objects.create(
+            requested_by=self.user,
+            archive_type='service_tasks',
+            year=2033,
+            month=12,
+            status='ready',
+            filename='stale-archive.zip',
+            expires_at=timezone.now() + timedelta(days=2),
+        )
+        stale.file.save('stale-archive.zip', ContentFile(b'OLD-ARCHIVE'), save=True)
+        stale_updated_at = timezone.now() - timedelta(days=1)
+        GeneratedFleetArchive.objects.filter(pk=stale.pk).update(updated_at=stale_updated_at)
+        self.task.service_report_note = 'Nova napomena nakon cache-a'
+        self.task.save()
+
+        response = self.client.post(
+            '/api/fleet/reports/monthly-service-tasks-archive-request/',
+            data={'year': 2033, 'month': 12},
+            format='json',
+        )
+        self.assertIn(response.status_code, [200, 202], response.content)
+        payload = response.json()
+        self.assertIn('generated_archive_id', payload)
+        self.assertNotEqual(str(stale.pk), str(payload['generated_archive_id']))
+
+        stale.refresh_from_db()
+        self.assertFalse(stale.is_active)
+        self.assertEqual(stale.status, 'failed')
+
     def test_monthly_work_orders_archive_request_creates_ready_download_with_notification(self):
         WorkOrderInvoice.objects.create(
             work_order=self.work_order,