Function windowed_fraction_for 

pub fn windowed_fraction_for(kind: BreakKind, s: &Settings) -> f64

Resolve the windowed-overlay size fraction for a break kind: the per-kind override when set, otherwise the global windowed_fraction. The result is clamped to [0.1, 1.0] (matching crate::scheduler::overlay::centered_windowed_rect) so a corrupt on-disk value can’t size the overlay off-screen. Sleep has no override and falls back to the global value (it never renders windowed anyway).