test(sidebar): align legacy list checks with visible-session filtering (#4775)

tests/test_session_import_cli_fallback_model.py

@@ -338,6 +338,7 @@ def test_sessions_endpoint_suppresses_duplicate_webui_state_projection(monkeypat
         "session_id": "visible_tip",
         "title": "Long Conversation",
         "profile": "default",
+        "message_count": 1,
         "updated_at": 20,
         "last_message_at": 20,
         "source_tag": "webui",
@@ -362,6 +363,7 @@ def test_sessions_endpoint_suppresses_duplicate_webui_state_projection(monkeypat
         "session_id": "telegram_tip",
         "title": "External Thread",
         "profile": "default",
+        "message_count": 1,
         "updated_at": 10,
         "last_message_at": 10,
         "source_tag": "telegram",