Casting to InputSchema drops $defs, causing an InternalServerError

Problem

Consider a tool-calling request with the following schema: [code block] Anthropic correctly handles this so long as `$defs` is present; should it be dropped, the `enum` fields become unresolvable, causing an error of the form of: [code block] Unfortunately, using `pydantic.TypeAdapter(anthropic.types.beta.tools.tool_param.InputSchema).validate_python(tool.model_json_schema())` drops the `$defs` field from the representation -- after getting the aforementioned HTTP 500 error, if we walk the stack up to `anthropic._base_client.post`, we see a body where `$defs` is not present at all, despite references to it existing: [code block] ...thus explaining the HTTP 500. And, indeed, if the use of `pydantic.TypeAdapter(InputSchema).validate_python(tool.model_json_schema())` is replaced with `typing.cast(InputSchema, tool.model_json_schema())`, the issue is resolved. This is unfortunate: Users of this library should not need to give up type safety to avoid triggering server-side errors.