test(systems): fix two mock bugs in the seam tests — unset .id on the fake, shared to_dict dict leaking across creates

Runs 3562/3565: _fake_system never sets .id so the dup-gate assertion
compared a MagicMock to 7; and a shared to_dict return_value dict let
the tagged create's mutation leak into the orphan create's response.

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

tests/test_mcp_tool_systems.py

@@ -106,6 +106,7 @@ async def test_untagged_hint_zero_systems_prompts_first_create_and_fails_open():
 @pytest.mark.asyncio
 async def test_create_system_same_normalized_name_is_duplicate_gated():
     existing = _fake_system(sid=7, name="Scrape Pipeline")
+    existing.id = 7
     existing.name = "Scrape Pipeline"
     with patch("scribe.mcp.tools.systems.current_user_id", return_value=1), \
          patch("scribe.mcp.tools.systems.systems_svc") as svc:
@@ -150,7 +151,10 @@ async def test_create_task_untagged_in_project_carries_the_question():
 
 @pytest.mark.asyncio
 async def test_create_task_tagged_shows_systems_and_projectless_gets_neither():
-    note = MagicMock(); note.id = 61; note.to_dict.return_value = {"id": 61}
+    note = MagicMock(); note.id = 61
+    # Fresh dict per call — a shared return_value dict lets the first create's
+    # mutation leak into the second create's response.
+    note.to_dict.side_effect = lambda: {"id": 61}
     tagged_sys = MagicMock(); tagged_sys.to_dict.return_value = {"id": 4, "name": "plugin-hooks"}
     with patch("scribe.mcp.tools.tasks.current_user_id", return_value=1), \
          patch("scribe.mcp.tools.tasks.notes_svc") as notes_svc, \