I am in the process of migrating some QGIS 2.x processing toolbox script to QGIS 3.x.
I have a collection of scripts that helps in the seismic 3D planning and geometry processing.
One of the scripts is partially working, that is it generates the output layer as expected. For the version 2.x framework I had defined:
##CSV_for_SPS_Generation=output table ##Generated_Lines_Layer=output vector
That CSV is, in reality, a log of the run. It is not meant to be a layer in itself. When running the script the file was generated and automagically loaded as a table without geometry, even as a temporary file.
I was not able to find a solution that could define a file, temporary or otherwise, that would be loaded at the end of the process as a table.