Drop the docs note

Author: maxisbey

docs/advanced/low-level-server.md

@@ -121,7 +121,6 @@ The server never compares the two fields. This SDK's `Client` does: return `stru
 
 * The root of `input_schema` must be `"type": "object"`. Beside it, `oneOf`, `additionalProperties`, `anyOf`, `if`/`then`/`else`, `prefixItems`, `$defs` with local `$ref`s and the rest of the 2020-12 keywords reach the client exactly as written.
 * No `$schema` key is needed. Add one only to opt into an older draft: this SDK's `Client`, which validates `structured_content` against a tool's `output_schema`, picks its validator from `$schema` and uses 2020-12 when there is none.
-* Keep `$ref`s inside the schema (`#/$defs/...`, `$anchor`, an embedded `$id`). The `Client` never fetches a reference to another document, URL or file: a result whose validation reaches one fails with a `RuntimeError` that starts with `Invalid schema for tool <name>`.
 
 ## `_meta`: for the application, not the model