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_retrieval_scopes.py

@@ -15,7 +15,7 @@ shared record would be findable by wording and invisible by meaning.
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
-from tests.helpers import fake_note
+from tests.helpers import fake_note, make_mock_session
 
 
 pytestmark = pytest.mark.usefixtures("_no_supersession")
@@ -95,9 +95,7 @@ async def test_hybrid_search_halves_agree_on_scope():
          patch.object(knowledge, "readable_notes_clause",
                       MagicMock(return_value=(Note.user_id == 7))) as read_clause, \
          patch.object(knowledge, "async_session") as sess:
-        session = AsyncMock()
-        session.__aenter__ = AsyncMock(return_value=session)
-        session.__aexit__ = AsyncMock(return_value=False)
+        session = make_mock_session()
         result = MagicMock()
         result.scalars.return_value.all.return_value = []
         session.execute = AsyncMock(return_value=result)