refactor(backend): consolidate thread_id resolution into shared get_thread_id() utility (#2522)

Extract duplicated thread_id fallback logic from 11 files into a single
  deerflow.utils.runtime.get_thread_id() function with a documented 3-level
  cascade (runtime.context → runtime.config → get_config()).

  The module docstring also clarifies the __pregel_runtime injection pattern used in
  gateway mode.

backend/packages/harness/deerflow/agents/middlewares/memory_middleware.py

@@ -5,12 +5,12 @@ from typing import override
 
 from langchain.agents import AgentState
 from langchain.agents.middleware import AgentMiddleware
-from langgraph.config import get_config
 from langgraph.runtime import Runtime
 
 from deerflow.agents.memory.message_processing import detect_correction, detect_reinforcement, filter_messages_for_memory
 from deerflow.agents.memory.queue import get_memory_queue
 from deerflow.config.memory_config import get_memory_config
+from deerflow.utils.runtime import get_thread_id
 
 logger = logging.getLogger(__name__)
 
@@ -57,11 +57,8 @@ class MemoryMiddleware(AgentMiddleware[MemoryMiddlewareState]):
         if not config.enabled:
             return None
 
-        # Get thread ID from runtime context first, then fall back to LangGraph's configurable metadata
-        thread_id = runtime.context.get("thread_id") if runtime.context else None
-        if thread_id is None:
-            config_data = get_config()
-            thread_id = config_data.get("configurable", {}).get("thread_id")
+        # Get thread ID from runtime context
+        thread_id = get_thread_id(runtime)
         if not thread_id:
             logger.debug("No thread_id in context, skipping memory update")
             return None