Use precise types instead of Any, and avoid unnecessary typing.cast by relying on type-guard utilities and existing type narrowing. In tests, prefer the concrete pytest types/fixtures (e.g., pytest.MonkeyPatch) over broad Any.

Apply this as a style rule:

• Don’t annotate parameters/locals as Any when a concrete type exists.
• If you’re doing typing.cast purely to satisfy typing after runtime checks, prefer type-guard helpers (e.g., is_dict, is_list) that narrow types.
• If static analysis (e.g., pyright) already succeeds without a cast, remove it.

Example:

import pytest
import typing as t
from .typing_utils import is_dict, is_list

@pytest.mark.respx()
def test_something(monkeypatch: pytest.MonkeyPatch) -> None:
    ...

def _deep_merge_extra_fields(existing: object, new: object) -> object:
    if is_dict(existing) and is_dict(new):
        # type is narrowed by is_dict
        for k, v in new.items():
            ...
        return existing
    if is_list(existing) and is_list(new):
        # type is narrowed by is_list
        existing.extend(new)
        return existing
    return new