refactor(tests): per-model fakes, FakeMCP and session mocks come from tests/helpers (#2825, milestone 296 area 1, batch 2)

Second pass over the tests/ ledger after bbee0d0. fake_record(**attrs) is the
one MagicMock-with-real-attributes builder (to_dict mirrors them; the
note-2109 hazard documented once); fake_note/fake_task/fake_snippet/
fake_project/fake_milestone/fake_system/fake_rulebook/fake_topic/fake_rule
carry each model's ordinary defaults on top of it, replacing 14 per-file
factories (two rulebook trios in tool-vs-service wordings, _fake_task, _fake_ms,
_fake_project, _plan_note, _fake_snippet, two _snippet adapters now one-liners
over fake_snippet). FakeMCP replaces the five closure-over-a-list registrar
fakes (+ _Recorder); loc() and design_token_stub() replace the paired _loc /
_token / _T stand-ins; every hand-built async_session mock (9 helper defs and
14 inline copies) now starts from make_mock_session(). Call sites rewritten by
AST with each file's former defaults made explicit, so behaviour is unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_services_db_maintenance.py

@@ -9,6 +9,7 @@ from unittest.mock import AsyncMock, MagicMock, patch
 import pytest
 
 from scribe.services.db_maintenance import MAINTENANCE_TABLES, run_maintenance
+from tests.helpers import make_mock_session
 
 
 def _mock_engine(exec_side_effect=None):
@@ -79,9 +80,7 @@ async def test_one_table_failure_does_not_abort_the_rest():
 
 
 def _health_session(db_bytes, rows):
-    s = AsyncMock()
-    s.__aenter__ = AsyncMock(return_value=s)
-    s.__aexit__ = AsyncMock(return_value=False)
+    s = make_mock_session()
     size_res = MagicMock()
     size_res.scalar.return_value = db_bytes
     rows_res = MagicMock()