This traces planar lightprobe captures just like the screen-space tracing does. This is implemented as a separate shader that loads the ray before the screen trace and check if it can be traced against any available planar probe. If it does it marks the ray as traced (negative pdf) so that the screen tracing pass does not override the result or try to trace it. Pull Request: https://projects.blender.org/blender/blender/pulls/113453