A root-level field accepts a value its declaration refuses; a nested field raises #47

What happens at 1fcdf12: update_parameter("ui.column_width", 4) on a nested field rebuilds the owning dataclass (_dataclass_ancestor_parameter_updates, src/objectstate/object_state.py:844), so a dataclass whose __post_init__ refuses the value raises and the state is left unchanged. For a field of the root object the function returns {} at its first line ("." not in param_name), nothing is constructed, the value is stored, subscribers are told it changed, and the refusal only appears later, at to_object() (:2607), far from the edit and after dirty_fields and every subscriber have already taken the bad value.

So whether an invalid edit is refused depends on how deep the field is.

Wanted: one rule for every depth: update_parameter constructs the object the new parameters describe before storing them, and raises without mutating when the declaration refuses it.

Workaround in Toad now: toad.forms.declared_views.DeclaredField.edit calls python_introspect.validation.validate_annotation_value on the field's annotation before update_parameter.

Acceptance: for @dataclass class Root(AnnotatedDataclassValidationMixin): count: Annotated[int, Ge(1)] = 3, ObjectState(Root()).update_parameter("count", 0) raises ValueError, parameters["count"] is still 3, no change callback fires and dirty_fields is empty.