Function pulse_delta 

pub fn pulse_delta(spec: &MotionSpec, painter: Painter, cx: &mut App) -> f32

Current phase [0,1) of a repeating spec, plus a [lease] that keeps the calling view re-rendering at [PULSE_FPS] while its spinner stays mounted. All cells across all views share one epoch, so multi-instance loaders stay phase-locked. Reduced motion returns a static 0 and schedules nothing.