How do I configure a light's colorContribution attribute to render only shadows in TSL?

Hello community,

I am porting a legacy architecture to the new TSL system and trying to implement a colorContribution property on lighting to configure a light that produces only shadows for real-time rendering. I attempted to bypass the color rendering by modifying the setup of a directional light node as shown below:

JAVASCRIPTCopied
setup( builder ) {

    super.setup( builder );

    const lightingModel = builder.context.lightingModel;

    const lightColor = this.colorNode;
    const lightDirection = lightTargetDirection( this.light );
    const reflectedLight = builder.context.reflectedLight;

    if( this.light.colorContribution == true ){
        lightingModel.direct( {
            lightDirection,
            lightColor,
            reflectedLight
        }, builder.stack, builder );
    }
}

However, bypassing the call to lightingModel.direct prevents the corresponding shadow node from being pushed into the updateBeforeNodes map, which in turn disrupts shadow updates. I have been debugging this issue extensively without success and suspect there may be underlying internal mechanisms I am not aware of.

Any help or insights would be greatly appreciated.