Add reserved arg names to tools (#1553)

Fixes DOC-475

Author: lnhsingh

src/oss/langchain/tools.mdx

@@ -138,6 +138,18 @@ Define complex inputs with Pydantic models or JSON schemas:
         return result
     ```
 </CodeGroup>
+
+:::python
+### Reserved argument names
+
+The following parameter names are reserved and cannot be used as tool arguments. Using these names will cause runtime errors.
+
+| Parameter name | Purpose |
+|----------------|---------|
+| `config` | Reserved for passing `RunnableConfig` to tools internally |
+| `runtime` | Reserved for `ToolRuntime` parameter (accessing state, context, store) |
+
+To access runtime information, use the @[`ToolRuntime`] parameter instead of naming your own arguments `config` or `runtime`.
 :::
 
 ## Accessing Context