Keep mouse within area in Swift

Question

I'm trying to prevent the mouse cursor from leaving a specific area of the screen. I can't find a native method to do this, so I'm trying to do it manually.

So far I have this:

NSEvent.addGlobalMonitorForEvents(matching: [.mouseMoved, .leftMouseDragged], handler: {(event: NSEvent) in
    let x = event.locationInWindow.flipped.x;
    let y = event.locationInWindow.flipped.y;
        
    if (x <= 100) {
        CGWarpMouseCursorPosition(CGPoint(x: 100, y: y))
    }
})

// elsewhere to flip y coordinates
extension NSPoint {
    var flipped: NSPoint {
        let screenFrame = (NSScreen.main?.frame)!
        let screenY = screenFrame.size.height - self.y
        return NSPoint(x: self.x, y: screenY)
    }
}

This stops the cursor from going off the X axis. Great. But it also stops the cursor from sliding along the y axis at X=100.

So I tried to add the delta:

NSEvent.addGlobalMonitorForEvents(matching: [.mouseMoved, .leftMouseDragged], handler: {(event: NSEvent) in
    let x = event.locationInWindow.flipped.x;
    let y = event.locationInWindow.flipped.y;
    let deltaY = event.deltaY;
        
    if (x <= 100) {
        CGWarpMouseCursorPosition(CGPoint(x: 100, y: y + deltaY))
    }
})

Now it does slide along the Y axis. But the acceleration is way off, it's too fast. What I don't get is that if I try to do y - deltaY it slides like I expect, but reversed:

NSEvent.addGlobalMonitorForEvents(matching: [.mouseMoved, .leftMouseDragged], handler: {(event: NSEvent) in
    let x = event.locationInWindow.flipped.x;
    let y = event.locationInWindow.flipped.y;
    let deltaY = event.deltaY;
        
    if (x <= 100) {
        CGWarpMouseCursorPosition(CGPoint(x: 100, y: y - deltaY))
    }
})

Now the cursor is sliding along the Y axis at X=100 with proper acceleration (like sliding the cursor against the edge of the screen), but it's reversed. Moving the mouse up, moves the cursor down.

How do I get proper smooth sliding of the cursor, in the proper direction, at the edge of my custom area?

Or is there a better way to achieve what I'm trying to do?