Old workflows (saved before the control_after_generate feature) carry a
shorter widgets_values array. The frontend's index-based widget restore
then shifts the old weight_dtype value into the hidden control widget
(leaving an invalid value like 'default') and silently resets
weight_dtype to its default. On graph load, hand the shifted value back
to weight_dtype when it still sits at its default, then reset the
control mode to 'fixed' so old workflows keep loading deterministically.
Will Miao