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_shared_write_access.py

@@ -10,24 +10,17 @@ A record readable-but-not-writable raises PermissionError rather than reporting
 "not found" — the caller can plainly open it, so not-found would be a lie that
 sends them hunting for a missing id.
 """
-from unittest.mock import AsyncMock, MagicMock, patch
+from unittest.mock import AsyncMock, patch
 
 import pytest
+from tests.helpers import fake_snippet
 
 
 def _snippet(id=1, owner=9):
-    n = MagicMock()
-    n.id = id
-    n.user_id = owner
-    n.title = "formatDuration — humanize a millisecond count"
-    n.body = "```ts\nexport const f = 1\n```\n"
-    n.tags = ["ts", "snippet"]
-    n.note_type = "snippet"
-    n.deleted_at = None
-    # Explicitly None — snippet_fields prefers `data` when truthy, and an
-    # auto-MagicMock attribute is truthy (see note 2109).
-    n.data = None
-    return n
+    return fake_snippet(
+        id=id, user_id=owner, title="formatDuration — humanize a millisecond count",
+        body="```ts\nexport const f = 1\n```\n", tags=["ts", "snippet"],
+    )
 
 
 @pytest.mark.asyncio