Set up document management for Stirling Engine (#6476)

# Description of Changes
Change Stirling Engine to support deleting documents automatically. This
happens both on user logout and after an amount of time specified by the
Java when ingesting a document (allowing for personal documents to have
short lifetimes but org documents to be left in the db with no expiry
date). Also sets up an [ACL
policy](https://en.wikipedia.org/wiki/Access-control_list) for the
documents so the database knows which users have access to which
documents. This is not fully implemented in the Java, so currently all
docs are treated as having a single owner, the uploader, but
theoretically when we need to support org storage, we shouldn't need to
change the db schema.

engine/tests/contradiction/test_question_integration.py

@@ -9,6 +9,7 @@ detector when invoked.
 
 from __future__ import annotations
 
+from collections.abc import Iterator
 from dataclasses import replace
 
 import pytest
@@ -22,10 +23,24 @@ from stirling.contracts import (
 )
 from stirling.contracts.contradiction import Claim
 from stirling.documents import DocumentService, SqliteVecStore
-from stirling.models import FileId
+from stirling.models import FileId, OwnerId, PrincipalId, UserId
+from stirling.services import current_user_id
 from stirling.services.runtime import AppRuntime
 from tests.test_pdf_question_agent import StubEmbedder
 
+USER = UserId("test-user")
+OWNER = OwnerId("test-user")
+OWNER_PRINCIPALS = [PrincipalId("test-user")]
+
+
+@pytest.fixture(autouse=True)
+def _set_user_context() -> Iterator[None]:
+    token = current_user_id.set(USER)
+    try:
+        yield
+    finally:
+        current_user_id.reset(token)
+
 
 def _file(file_id: str, name: str) -> AiFile:
     return AiFile(id=FileId(file_id), name=name)
@@ -69,6 +84,9 @@ async def test_run_answer_agent_builds_agent_with_three_toolsets(
         file.id,
         [PageText(page_number=1, text="content")],
         source=file.name,
+        owner_id=OWNER,
+        read_principals=OWNER_PRINCIPALS,
+        expires_at=None,
     )
 
     agent = PdfQuestionAgent(runtime_with_stub_docs)