The `covariant` Keyword: Loosening Type Rules

The `covariant` keyword tells Dart's analyzer to relax its strict rules for method overriding. It lets a subclass method accept a more specific parameter type than its parent, which is normally a type safety violation. This is common in Flutter, where a parent widget's method might accept a generic `Widget`, but a subclass needs a specific `Text` widget. The footgun: misusing `covariant` trades a compile-time error for a potential runtime crash if an incorrect type is passed.