[Core] Add more interops tests (#26841)

To test that the client propagates both ways

libs/core/langchain_core/callbacks/manager.py

@@ -2333,7 +2333,11 @@ def _configure(
                 try:
                     handler = LangChainTracer(
                         project_name=tracer_project,
-                        client=run_tree.client if run_tree is not None else None,
+                        client=(
+                            run_tree.client
+                            if run_tree is not None
+                            else tracing_context["client"]
+                        ),
                     )
                     callback_manager.add_handler(handler, True)
                 except Exception as e:

libs/core/langchain_core/tracers/core.py

@@ -118,7 +118,7 @@ class _TracerCore(ABC):
                     self._add_child_run(parent_run, run)
             else:
                 if self.log_missing_parent:
-                    logger.warning(
+                    logger.debug(
                         f"Parent run {run.parent_run_id} not found for run {run.id}."
                         " Treating as a root run."
                     )

libs/core/langchain_core/tracers/langchain.py

@@ -123,7 +123,7 @@ class LangChainTracer(BaseTracer):
 
         super()._start_trace(run)
         if run._client is None:
-            run._client = self.client
+            run._client = self.client  # type: ignore
 
     def on_chat_model_start(
         self,