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032b9f6382* fix: don't infer an output schema for unconstrained sequences
`Any` is already excluded from output-schema inference because the schema
it produces constrains nothing. A bare `list` or `tuple` is the
sequence-shaped equivalent: it yields `{"result": {"items": {}, "type":
"array"}}`, which permits every value that no schema at all permits.
Inferring it is not free. An output schema forces structured content, and
`replace_type` cannot suppress the MCP content types inside a sequence
that has no item type to match -- which is why `list[ContentBlock]`
already infers nothing but bare `list` does not. So a tool annotated
`-> list` returning `[ImageContent(...), {...}]`, the shape used to pair
a picture with its metadata, puts the base64 image on the wire twice:
once as an image content block, and once again serialised into
`structuredContent`.
Clients break on that in both directions. Some render the JSON blob
instead of the picture; others inject the duplicated base64 into model
context and blow their tool-output token cap. Server authors currently
work around it per-tool with `output_schema=None`, which also discards
the schema for tools that wanted one.
`list`, `tuple`, `list[Any]` and `tuple[Any, ...]` now infer no schema,
matching `Any`. Annotations that say something about their items --
`list[int]`, `tuple[int, str]`, `dict`, `str` -- are untouched.
Two parametrized sweeps asserted the old bare-`list` schema as one case
among many annotations; `list` is dropped from both, and the new
behaviour gets its own tests including a regression test that a returned
image is not duplicated into `structuredContent`.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
* tools: catch typing.List, Sequence, and Annotated in the unconstrained-sequence guard
fixed-length tuple[Any, ...] variants keep their schema since they still
pin a length. documents the exception in the tools docs.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0186WjrVNudDm5qaDPw5mntN
---------
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Co-authored-by: zzstoatzz <thrast36@gmail.com>
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| .. | ||
| tool | ||
| tool_transform | ||
| __init__.py | ||
| test_standalone_decorator.py | ||
| test_tool_future_annotations.py | ||
| test_tool_run_in_thread.py | ||
| test_tool_timeout.py | ||