Constant PROVIDER_COST_CATEGORIES 

pub const PROVIDER_COST_CATEGORIES: [&str; 3];

The provider families that carry [cost.rates.providers.*] rate sheets, as the trailing segment shared by their [providers.<category>] section. One entry per #[nested] field on ProviderCostRates; this list is the registry the TUI and web surfaces resolve cost tabs from, never a per-surface literal.