refactor(core): remove redundant runtime scaffolding (#5127)

tests/test_openai_api.py

@@ -454,10 +454,12 @@ async def test_empty_response_falls_back_without_retry(aiohttp_client) -> None:
 async def test_process_direct_accepts_media() -> None:
     """process_direct should forward media paths to _process_message."""
     from nanobot.agent.loop import AgentLoop
+    from nanobot.bus.runtime_events import RuntimeEventPublisher
 
     loop = AgentLoop.__new__(AgentLoop)
     loop._connect_mcp = AsyncMock()
     loop._session_locks = {}
+    loop.runtime_event_publisher = RuntimeEventPublisher()
 
     captured_msg = None