items_to_messages method not handle "ResponseReasoningItemParam"

[goooodle]

Please read this first

• Have you read the docs?Agents SDK docs
• Have you searched for related issues? Others may have faced similar issues.

Yes

Describe the bug

@classmethod def items_to_messages( cls, items: str | Iterable[TResponseInputItem], ) -> list[ChatCompletionMessageParam]:

This method does not handle "ResponseReasoningItemParam",
So raise UserError(f"Unhandled item type or structure: {item}")

[dotmobo]

same error for me with LitellmModel, qwen 3 and a "/think" query.
result.stream_events() from Runner.run_streamed(...) raise that error.
i didn't have that error wih the 0.0.19 version of the lib.

[dotmobo]

same as #1164