fix: add null checks for runtime.context and tighten langgraph constraint (#1326)

- Add null checks for runtime.context in uploads_middleware.py and
  sandbox/middleware.py to prevent NPE when langgraph runtime context is None
- Tighten langgraph version constraint from >=1.0.6 to >=1.0.6,<1.0.10
  to avoid context=None incompatibility with langgraph-api 0.7.x

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

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

@@ -146,7 +146,7 @@ class UploadsMiddleware(AgentMiddleware[UploadsMiddlewareState]):
             return None
 
         # Resolve uploads directory for existence checks
-        thread_id = runtime.context.get("thread_id") if runtime.context else None
+        thread_id = (runtime.context or {}).get("thread_id")
         uploads_dir = self._paths.sandbox_uploads_dir(thread_id) if thread_id else None
 
         # Get newly uploaded files from the current message's additional_kwargs.files