# type: ignore[assignment] on the except ImportError: x = None fallback in serializer.py (pyarrow) and document_base.py (annotationlib, UnionType) flips between needed/unused depending on mypy/pyarrow-stubs/Python version. Hit twice already: generates_9.5_code (6b0aa4e, 408d9c9) and main (#3475). #3475 suppressed it via a module-wide warn_unused_ignores = false override, which also hides any real unused-ignore added to those files later.

Fix: split type-checking and runtime import paths, mypy always resolves the if branch, the else is never type-checked (verified: no error with pyarrow installed, uninstalled, or a garbage assignment in the except).

if TYPE_CHECKING:
    import pyarrow as pa
else:
    try:
        import pyarrow as pa
        ...
        __all__.append("PyArrowSerializer")
    except ImportError:
        pa = None

Same shape for annotationlib and UnionType. Remove the two overrides from pyproject.toml.

Rejected: annotate pa: Optional[ModuleType] upfront, skip the split. Fails with no-redef, mypy treats the annotation and the import as conflicting.

Effort: ~30-60 min, 2 files, verify across the Python version matrix.