fix(tasks): use TriggerSource enum values at all apply_async call sites

Replace raw strings ("system", "manual") with PaperlessTask.TriggerSource
enum values in the three callers that can import models. The settings
file remains a raw string (models cannot be imported at settings load
time) with a comment pointing to the enum value it must match.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/documents/views.py

@@ -3951,7 +3951,7 @@ class TasksViewSet(ReadOnlyModelViewSet[PaperlessTask]):
             task_func, task_kwargs = self._RUNNABLE_TASKS[task_type]
             async_result = task_func.apply_async(
                 kwargs=task_kwargs,
-                headers={"trigger_source": "manual"},
+                headers={"trigger_source": PaperlessTask.TriggerSource.MANUAL},
             )
             return Response({"task_id": async_result.id})
         except Exception as e:

src/paperless/settings/custom.py

@@ -183,6 +183,7 @@ def parse_beat_schedule() -> dict:
             "schedule": crontab(minute, hour, day_week, day_month, month),
             "options": {
                 **task["options"],
+                # PaperlessTask.TriggerSource.SCHEDULED -- models can't be imported here
                 "headers": {"trigger_source": "scheduled"},
             },
         }

src/paperless/views.py

@@ -38,6 +38,7 @@ from rest_framework.response import Response
 from rest_framework.throttling import ScopedRateThrottle
 from rest_framework.viewsets import ModelViewSet
 
+from documents.models import PaperlessTask
 from documents.permissions import PaperlessObjectPermissions
 from documents.tasks import llmindex_index
 from paperless.filters import GroupFilterSet
@@ -429,7 +430,7 @@ class ApplicationConfigurationViewSet(ModelViewSet[ApplicationConfiguration]):
             # AI index was just enabled and vector store file does not exist
             llmindex_index.apply_async(
                 kwargs={"rebuild": True},
-                headers={"trigger_source": "system"},
+                headers={"trigger_source": PaperlessTask.TriggerSource.SYSTEM},
             )
 
 

src/paperless_ai/indexing.py

@@ -39,7 +39,7 @@ def queue_llm_index_update_if_needed(*, rebuild: bool, reason: str) -> bool:
 
     llmindex_index.apply_async(
         kwargs={"rebuild": rebuild},
-        headers={"trigger_source": "system"},
+        headers={"trigger_source": PaperlessTask.TriggerSource.SYSTEM},
     )
     logger.warning(
         "Queued LLM index update%s: %s",