Instead of adding points to a temporary list stored in the Spline tool, which gets destructively committed when the user is done and turned into a Bezier curve, move that spline -> Bezier logic into a node and make the Spline tool draw a polyline which gets fed into the spline interpolator node.
Instead of adding points to a temporary list stored in the Spline tool, which gets destructively committed when the user is done and turned into a Bezier curve, move that spline -> Bezier logic into a node and make the Spline tool draw a polyline which gets fed into the spline interpolator node.