3204201360
When a tool’s output TypedDict uses total=False, MCP clients reject the
response with:
```
MCP error -32602: Structured content does not match the tool's output schema
```
Note that the bug also exists for the Engine transport
(/worker/tools/execute), but since the engine doesn't validate the
output schema, the bug never surfaced. This PR addresses the problem
holistically (MCP and Engine) in preparation for a future where the
Engine transport validates output schemas.
Two bugs combined to cause this:
1. Schema: The outputSchema had no required array and declared all
fields as strict types (e.g. "type": "string"), making every field look
mandatory and non-null.
2. Serialization: model_dump() on TypedDict-derived Pydantic models
emitted None for absent optional fields. A tool returning {"name":
"hello"} produced {"name": "hello", "optional_field": null} which is a
value the schema forbids.
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> **Medium Risk**
> Adjusts core schema generation and MCP JSON Schema conversion for
TypedDicts, affecting how tool input/output contracts are emitted and
validated across clients; mistakes could break compatibility or
validation behavior.
>
> **Overview**
> Fixes MCP/engine validation failures for `TypedDict(total=False)`
outputs by ensuring absent optional keys are **omitted from serialized
output** and that emitted schemas correctly describe **required vs
optional** keys.
>
> `arcade-core` now tracks `required_keys`/`inner_required_keys` and
per-field `nullable` in `ValueSchema`, derives required sets from
TypedDict `__required_keys__`, and unwraps `Optional[T]` to support
optional nested TypedDicts; TypedDict-derived Pydantic models now
`model_dump(exclude_unset=True)` to avoid leaking missing fields as
`null`.
>
> `arcade-mcp-server` JSON Schema conversion now emits `required` arrays
(including for arrays of objects), supports `nullable` by generating
`type: [<type>, "null"]` (and `enum` including `None`), and treats
nullable top-level objects as valid unwrapped output schemas. Adds
focused unit/end-to-end tests plus an expanded example server
demonstrating total-false, mixed required/optional, nullable, and
optional-nested TypedDict outputs, and bumps package
versions/dependencies accordingly.
>
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
53fe8365f613053599130520b75f30b614b465ca. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
47 lines
1.4 KiB
TOML
47 lines
1.4 KiB
TOML
[build-system]
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requires = ["hatchling>=1.25"]
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build-backend = "hatchling.build"
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[project]
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name = "arcade-mcp-server"
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version = "1.19.1"
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description = "Model Context Protocol (MCP) server framework for Arcade.dev"
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readme = "README.md"
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authors = [{ name = "Arcade.dev" }]
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license = { text = "MIT" }
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classifiers = [
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"Development Status :: 5 - Production/Stable",
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"Intended Audience :: Developers",
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"License :: OSI Approved :: MIT License",
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"Programming Language :: Python :: 3",
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"Programming Language :: Python :: 3.10",
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"Programming Language :: Python :: 3.11",
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"Programming Language :: Python :: 3.12",
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"Programming Language :: Python :: 3.13",
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]
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requires-python = ">=3.10"
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dependencies = [
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"arcade-core>=4.6.1,<5.0.0",
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"arcade-serve>=3.2.0,<4.0.0",
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"arcade-tdk>=3.6.0,<4.0.0",
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"arcadepy>=1.5.0",
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"pydantic>=2.0.0",
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"fastapi>=0.100.0",
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"uvicorn>=0.30.0",
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"watchfiles>=0.18.0", # included with uvicorn, but listed to be explicit
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"sse-starlette>=2.0.0",
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"starlette>=0.37.0",
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"anyio>=4.0.0",
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"python-dotenv>=1.0.0",
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"pydantic-settings>=2.10.1",
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"joserfc>=1.5.0",
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"httpx>=0.27.0,<1.0.0",
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"opentelemetry-api>=1.20.0",
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"opentelemetry-sdk>=1.20.0",
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]
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[project.optional-dependencies]
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dev = ["pytest>=8.0.0", "pytest-asyncio>=0.23.0", "mypy>=1.0.0", "ruff>=0.1.0"]
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[tool.hatch.build.targets.wheel]
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packages = ["arcade_mcp_server"]
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