fix(langgraph): key error on runtime for config w/o configurable (#6106)

Fixes https://github.com/langchain-ai/langgraph/issues/6072

Long term we probably want a more robust approach to configurable
management in terms of required / not required attributes.

libs/langgraph/langgraph/_internal/_runnable.py

@@ -345,7 +345,7 @@ class RunnableCallable(Runnable):
             args = (input,)
             kwargs = {**self.kwargs, **kwargs}
 
-        runtime = config[CONF].get(CONFIG_KEY_RUNTIME)
+        runtime = config.get(CONF, {}).get(CONFIG_KEY_RUNTIME)
 
         for kw, (runtime_key, default) in self.func_accepts.items():
             # If the kwarg is already set, use the set value
@@ -417,7 +417,7 @@ class RunnableCallable(Runnable):
             args = (input,)
             kwargs = {**self.kwargs, **kwargs}
 
-        runtime = config[CONF].get(CONFIG_KEY_RUNTIME)
+        runtime = config.get(CONF, {}).get(CONFIG_KEY_RUNTIME)
 
         for kw, (runtime_key, default) in self.func_accepts.items():
             # If the kwarg has already been set, use the set value

libs/langgraph/tests/test_runnable.py

@@ -394,3 +394,21 @@ def test_config_injection() -> None:
     assert RunnableCallable(func_untyped).invoke(
         "test", config={"tags": ["test"], "configurable": {}}
     ) == ["test"]
+
+
+def test_config_ensured() -> None:
+    def func(input: str, config: RunnableConfig) -> None:
+        assert input == "test"
+        assert config is not None
+        assert config.get("configurable") is not None
+
+    RunnableCallable(func).invoke("test")
+
+
+async def test_config_ensured_async() -> None:
+    async def func(input: str, config: RunnableConfig) -> None:
+        assert input == "test"
+        assert config is not None
+        assert config.get("configurable") is not None
+
+    await RunnableCallable(func).ainvoke("test")