Constant PRIORITY_LEVELS 

pub const PRIORITY_LEVELS: [Priority; 4];

The four priorities a board option can hold, in the order a new Priority field lists them. none is not among them: it is the field holding no value.

This list mirrors Priority, so it carries its own drift gate, in the shape CATEGORIES does: level_position is a wildcard-free match, so a priority added to the shared vocabulary fails to compile until it is placed there, and this crate’s suite reconciles this list and PriorityMappingConfig’s members against that enum’s own derived schema.