[Python] Generated date TypeAdapters fail mypy with Pydantic 2.14 #18156

The generated Python SDK fails its mypy compile check after the dependency lock upgrades Pydantic from 2.13.5 to 2.14.0.

Versions: Fern CLI 5.148.2, fernapi/fern-python-sdk 5.31.1, Python 3.11.15, mypy 1.13.0, Pydantic 2.14.0 (pydantic-core 2.50.0).

The generated core/pydantic_utilities.py contains:

if IS_PYDANTIC_V2:
    _datetime_adapter = pydantic.TypeAdapter(dt.datetime)  # type: ignore[attr-defined]
    _date_adapter = pydantic.TypeAdapter(dt.date)  # type: ignore[attr-defined]

The compile check reports:

error: Need type annotation for "_datetime_adapter" [var-annotated]
error: Need type annotation for "_date_adapter" [var-annotated]

A standalone reproduction requires no API schema:

import datetime as dt
import pydantic

_datetime_adapter = pydantic.TypeAdapter(dt.datetime)
_date_adapter = pydantic.TypeAdapter(dt.date)

Run mypy 1.13.0 on this file with Pydantic 2.14.0 installed: both errors reproduce. In a separate virtual environment with the same mypy version and Pydantic 2.13.5, the file type-checks successfully. The SDK's generated runtime lines are unchanged; the freshly generated dependency lock exposes the failure.

Please generate correctly typed date/datetime adapters that compile against supported Pydantic versions, and add coverage using Pydantic 2.14.0. The wheel and sdist still build and the SDK's runtime tests pass, but this blocks the generated compile job.

Generator upgrade check

The same unannotated declarations are present in the Python 5.34.2 release source (runtime template). Testing those exact declarations with mypy 1.13.0 and Pydantic 2.14.0 reproduces both errors, so that generator update does not contain this annotation fix.

The immediate workaround is to restore the previously working SDK lockfile versions: Pydantic 2.13.5 and pydantic-core 2.46.5.