refactor(config): eliminate global mutable state, wire DeerFlowContext into runtime

- Freeze all config models (AppConfig + 15 sub-configs) with frozen=True
- Purify from_file() — remove 9 load_*_from_dict() side-effect calls
- Replace mtime/reload/push/pop machinery with single ContextVar + init_app_config()
- Delete 10 sub-module globals and their getters/setters/loaders
- Migrate 50+ consumers from get_*_config() to get_app_config().xxx

- Expand DeerFlowContext: app_config + thread_id + agent_name (frozen dataclass)
- Wire into Gateway runtime (worker.py) and DeerFlowClient via context= parameter
- Remove sandbox_id from runtime.context — flows through ThreadState.sandbox only
- Middleware/tools access runtime.context directly via Runtime[DeerFlowContext] generic
- resolve_context() retained at server entry points for LangGraph Server fallback

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

@@ -6,11 +6,10 @@ from typing import Any, 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.queue import get_memory_queue
-from deerflow.config.memory_config import get_memory_config
+from deerflow.config.deer_flow_context import DeerFlowContext
 
 logger = logging.getLogger(__name__)
 
@@ -193,7 +192,7 @@ class MemoryMiddleware(AgentMiddleware[MemoryMiddlewareState]):
         self._agent_name = agent_name
 
     @override
-    def after_agent(self, state: MemoryMiddlewareState, runtime: Runtime) -> dict | None:
+    def after_agent(self, state: MemoryMiddlewareState, runtime: Runtime[DeerFlowContext]) -> dict | None:
         """Queue conversation for memory update after agent completes.
 
         Args:
@@ -203,15 +202,11 @@ class MemoryMiddleware(AgentMiddleware[MemoryMiddlewareState]):
         Returns:
             None (no state changes needed from this middleware).
         """
-        config = get_memory_config()
-        if not config.enabled:
+        memory_config = runtime.context.app_config.memory
+        if not memory_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")
+        thread_id = runtime.context.thread_id
         if not thread_id:
             logger.debug("No thread_id in context, skipping memory update")
             return None