Constant MIN_USEFUL_THICKNESS 

pub const MIN_USEFUL_THICKNESS: f32 = _; // 0.166666672f32

The thickness at which MIN_HALF_WIDTH stops binding — about 0.167.

Below this every value renders identically, because they all clamp to the same floor: a dead zone about 0.27 px wide at 1080p, which rasterizes as a broken dotted line rather than as a stroke. Derived from the two constants above rather than written out, so the load-time warning that quotes it (preset::schema) cannot drift from the floor it describes.