Make intermediate render results available in python

Sometimes it is useful to do some post-processing with the render results in a script. This is especially true, if you have multiple view_layers with separate outputs, but only the Composite node output is available in bpy.data.images['Render Result'] .

At the moment one has to use a File Output node, write to and reload from disk and handle the temporary files or use a TempDirectory like this:

    with tempfile.TemporaryDirectory() as temp_dir:
       bpy.context.scene.node_tree.nodes["FileOutput"].base_path = temp_dir
       bpy.ops.render.render(write_still=False)
       # load temp files and do stuff here

This approach is inefficient, unintuitive and error-prone (e.g. file names due to wrong frame, etc.)

A way to access these images in code would really be helpful. There is an options in the UI using ViewNode->Rightside Toolbar->"Save this Image", but testing for an extensive period of time I was not able to access this functionality in code (using blender as python module).