Immutability — E0040–E0043

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BSK-E0040 — Mutation of immutable parameter

A parameter without an InOut annotation is mutated.

def process(items: list[int]) -> None:
    items.append(99)  # Error — items is immutable by default

Fix by declaring intent:

from typing import Annotated
from basilisk import InOut

def process(items: Annotated[list[int], InOut]) -> None:
    items.append(99)  # OK — InOut declares mutation intent

BSK-E0041 — Reassignment of immutable parameter

A parameter is reassigned to a new value within the function body.

BSK-E0042 — Mutable dataclass (prefer frozen=True)

A @dataclass is defined without frozen=True. Frozen dataclasses are safer and work well with Basilisk's immutability model.

BSK-E0043 — Mutation of Final variable

A variable annotated with Final is reassigned.