style: align test conventions with existing codebase

- Prefix unused mock params with _ and type as Any
- Extract shared db session mock setup into helper
- Remove unused pytest import
- Use module path constant to reduce repetition

backend/ee/onyx/background/celery/tasks/ttl_management/tasks.py

@@ -54,27 +54,35 @@ def perform_ttl_management_task(
                 retention_limit_days, db_session
             )
 
+        failures = 0
         for user_id, session_id in old_chat_sessions:
-            # one session per delete so that we don't blow up if a deletion fails.
-            with get_session_with_current_tenant() as db_session:
-                delete_chat_session(
-                    user_id,
-                    session_id,
-                    db_session,
-                    include_deleted=True,
-                    hard_delete=True,
+            try:
+                with get_session_with_current_tenant() as db_session:
+                    delete_chat_session(
+                        user_id,
+                        session_id,
+                        db_session,
+                        include_deleted=True,
+                        hard_delete=True,
+                    )
+            except Exception:
+                failures += 1
+                logger.exception(
+                    "Failed to delete chat session "
+                    f"user_id={user_id} session_id={session_id}, "
+                    "continuing with remaining sessions"
                 )
 
         with get_session_with_current_tenant() as db_session:
             mark_task_as_finished_with_id(
                 db_session=db_session,
                 task_id=task_id,
-                success=True,
+                success=failures == 0,
             )
 
     except Exception:
         logger.exception(
-            f"delete_chat_session exceptioned. user_id={user_id} session_id={session_id}"
+            f"TTL management task failed. user_id={user_id} session_id={session_id}"
         )
         with get_session_with_current_tenant() as db_session:
             mark_task_as_finished_with_id(

backend/onyx/db/chat.py

@@ -185,7 +185,15 @@ def delete_messages_and_files_from_chat_session(
     for _, files in messages_with_files:
         file_store = get_default_file_store()
         for file_info in files or []:
-            file_store.delete_file(file_id=file_info.get("id"))
+            try:
+                file_store.delete_file(file_id=file_info.get("id"))
+            except Exception:
+                logger.warning(
+                    "Failed to delete file %s from file store during "
+                    "chat session cleanup, skipping.",
+                    file_info.get("id"),
+                )
+                continue
 
     # Delete ChatMessage records - CASCADE constraints will automatically handle:
     # - ChatMessage__StandardAnswer relationship records

backend/tests/unit/ee/onyx/background/celery/tasks/ttl_management/test_ttl_task.py

@@ -0,0 +1,109 @@
+"""Tests for TTL management task resilience."""
+
+from typing import Any
+from unittest.mock import MagicMock
+from unittest.mock import patch
+from uuid import uuid4
+
+
+_TASK_MODULE = "ee.onyx.background.celery.tasks.ttl_management.tasks"
+
+
+def _setup_db_session_mock(mock_get_db_session: MagicMock) -> None:
+    mock_db_session = MagicMock()
+    mock_get_db_session.return_value.__enter__ = MagicMock(
+        return_value=mock_db_session
+    )
+    mock_get_db_session.return_value.__exit__ = MagicMock(return_value=False)
+
+
+@patch(f"{_TASK_MODULE}.get_session_with_current_tenant")
+@patch(f"{_TASK_MODULE}.delete_chat_session")
+@patch(f"{_TASK_MODULE}.get_chat_sessions_older_than")
+@patch(f"{_TASK_MODULE}.mark_task_as_finished_with_id")
+@patch(f"{_TASK_MODULE}.register_task")
+def test_ttl_task_continues_after_session_delete_failure(
+    _mock_register: Any,
+    mock_mark_finished: MagicMock,
+    mock_get_old_sessions: MagicMock,
+    mock_delete_session: MagicMock,
+    mock_get_db_session: MagicMock,
+) -> None:
+    """One failing session should not prevent cleanup of remaining sessions."""
+    from ee.onyx.background.celery.tasks.ttl_management.tasks import (
+        perform_ttl_management_task,
+    )
+
+    user1, session1 = uuid4(), uuid4()
+    user2, session2 = uuid4(), uuid4()
+    user3, session3 = uuid4(), uuid4()
+
+    mock_get_old_sessions.return_value = [
+        (user1, session1),
+        (user2, session2),
+        (user3, session3),
+    ]
+
+    # Second session fails
+    mock_delete_session.side_effect = [
+        None,
+        RuntimeError("File does not exist"),
+        None,
+    ]
+
+    _setup_db_session_mock(mock_get_db_session)
+
+    mock_task = MagicMock()
+    mock_task.request.id = "test-task-id"
+
+    # Call the underlying function directly, bypassing Celery decorator
+    perform_ttl_management_task.__wrapped__(
+        mock_task, retention_limit_days=30, tenant_id="test"
+    )
+
+    # All three sessions should have been attempted
+    assert mock_delete_session.call_count == 3
+
+    # Task marked as finished with success=False (due to the one failure)
+    mock_mark_finished.assert_called()
+    finish_call_kwargs = mock_mark_finished.call_args[1]
+    assert finish_call_kwargs["success"] is False
+
+
+@patch(f"{_TASK_MODULE}.get_session_with_current_tenant")
+@patch(f"{_TASK_MODULE}.delete_chat_session")
+@patch(f"{_TASK_MODULE}.get_chat_sessions_older_than")
+@patch(f"{_TASK_MODULE}.mark_task_as_finished_with_id")
+@patch(f"{_TASK_MODULE}.register_task")
+def test_ttl_task_reports_success_when_all_deletions_pass(
+    _mock_register: Any,
+    mock_mark_finished: MagicMock,
+    mock_get_old_sessions: MagicMock,
+    mock_delete_session: MagicMock,
+    mock_get_db_session: MagicMock,
+) -> None:
+    """Task should report success when all sessions are deleted."""
+    from ee.onyx.background.celery.tasks.ttl_management.tasks import (
+        perform_ttl_management_task,
+    )
+
+    mock_get_old_sessions.return_value = [
+        (uuid4(), uuid4()),
+        (uuid4(), uuid4()),
+    ]
+    mock_delete_session.side_effect = None
+
+    _setup_db_session_mock(mock_get_db_session)
+
+    mock_task = MagicMock()
+    mock_task.request.id = "test-task-id"
+
+    perform_ttl_management_task.__wrapped__(
+        mock_task, retention_limit_days=30, tenant_id="test"
+    )
+
+    assert mock_delete_session.call_count == 2
+
+    mock_mark_finished.assert_called()
+    finish_call_kwargs = mock_mark_finished.call_args[1]
+    assert finish_call_kwargs["success"] is True

backend/tests/unit/onyx/db/test_chat_deletion.py

@@ -0,0 +1,58 @@
+"""Tests for chat session and message deletion resilience."""
+
+from typing import Any
+from unittest.mock import MagicMock
+from unittest.mock import patch
+from uuid import uuid4
+
+from onyx.db.chat import delete_messages_and_files_from_chat_session
+
+
+@patch("onyx.db.chat.delete_orphaned_search_docs")
+@patch("onyx.db.chat.get_default_file_store")
+def test_delete_messages_skips_missing_files(
+    mock_get_file_store: MagicMock,
+    _mock_delete_orphaned: Any,
+) -> None:
+    """Deletion should continue when a referenced file record no longer exists."""
+    session_id = uuid4()
+
+    file_store = MagicMock()
+    file_store.delete_file.side_effect = [
+        None,  # first file deletes fine
+        RuntimeError("File by id abc does not exist or was deleted"),
+        None,  # third file deletes fine
+    ]
+    mock_get_file_store.return_value = file_store
+
+    mock_db_session = MagicMock()
+    mock_db_session.execute.return_value.fetchall.return_value = [
+        (1, [{"id": "file-ok-1"}, {"id": "file-missing"}, {"id": "file-ok-2"}]),
+    ]
+
+    delete_messages_and_files_from_chat_session(session_id, mock_db_session)
+
+    assert file_store.delete_file.call_count == 3
+    mock_db_session.execute.assert_called()
+    mock_db_session.commit.assert_called()
+
+
+@patch("onyx.db.chat.delete_orphaned_search_docs")
+@patch("onyx.db.chat.get_default_file_store")
+def test_delete_messages_succeeds_with_no_files(
+    mock_get_file_store: MagicMock,
+    _mock_delete_orphaned: Any,
+) -> None:
+    """Deletion works when messages have no attached files."""
+    session_id = uuid4()
+
+    mock_db_session = MagicMock()
+    mock_db_session.execute.return_value.fetchall.return_value = [
+        (1, None),
+        (2, []),
+    ]
+
+    delete_messages_and_files_from_chat_session(session_id, mock_db_session)
+
+    mock_get_file_store.return_value.delete_file.assert_not_called()
+    mock_db_session.commit.assert_called()