Constant QUANT_SCALES 

pub const QUANT_SCALES: [&str; 7];

The scales quiver’s ScaleQuantizer selects between, in its own index order — which is not quiver::modules::Scale’s.

ScaleQuantizer does not use that enum at all: it matches on (scale_cv · 6.99) as u8 against its own inline table of seven scales (utilities.rs), and Mixolydian — index 6 of the eight-member Scale enum — is simply absent from it. Taking Scale’s order would have selected blues whenever the plate said mixolydian, and nothing at all for blues.