Function validate_answer_feedback_shape 

pub fn validate_answer_feedback_shape(
    mode: ClassifierTrainingMode,
    feedback: [u32; 3],
    reference: [u32; 3],
    output_shapes: &[[u32; 3]],
) -> Result<(), String>

Answer feedback must match the classifier output.

Kernel mode compares the class area. Scanner mode compares each detection twin. With no twin yet, the mask width, height, and depth are that output.