Masking problem in SwiftUI

I am engaged on a customized slider utilizing a RoundedRectangle for the monitor with one other Rectangle for the progress with a masks utilized. This largely works high quality so long as the thumb shouldn’t be near the tip. Because the thumb is dragged near the fitting aspect edge, the RoundedRectangle seems to be rounded at each ends. How can I repair it such that solely the fitting finish of the rounded rectangle reveals as rounded ?

struct Slider: View {
    @Binding var progress: CGFloat
    non-public let stroke: CGFloat = 5.0
    non-public var thumbWidth: CGFloat { stroke * 2 }
    non-public var thumbHeight: CGFloat { thumbWidth * 3.5 }
    
    var physique: some View {
        GeometryReader { geometry in
            
            ZStack {
                Shade.black.ignoresSafeArea()
                
                VStack {
                    let progressWidth = geometry.measurement.width * progress
                    let sliderWidth = geometry.measurement.width - thumbWidth
                    
                    ZStack(alignment: .main) {
                        RoundedRectangle(cornerRadius: stroke)
                            .body(peak: stroke)
                            .foregroundStyle(Shade.white.opacity(0.5))
                            .padding(.main, progressWidth)
                        
                        Rectangle()
                            .fill(Shade.white.opacity(0.5))
                            .masks(alignment: .main) {
                                Rectangle()
                                    .body(width: progressWidth)
                            }
                        
                        Capsule()
                            .fill(.purple)
                            .body(width: thumbWidth, peak: thumbHeight)
                            .offset(x: progress * (geometry.measurement.width - thumbWidth))
                            .gesture(
                                DragGesture()
                                    .onChanged { gesture in
                                        let newProgress = min(max(gesture.location.x / sliderWidth, 0), 1)
                                        progress = newProgress
                                    }
                            )
                    }
                    .body(peak: thumbHeight)
                }
            }
        }
    }
}

struct SliderView: View {
    @State non-public var progress: CGFloat = 0.0
    var physique: some View {
        ZStack {
            Shade.black.ignoresSafeArea()
            Slider(progress: $progress)
        }
    }
}

With thumb within the center:

With thumb near the tip: