more robust Position.setmp_thread_data, independently of Output.debugging (essentially reverts f9ec18f7c0f6, which was motivated by clean exception_trace, but without transaction positions the Isabelle_Process protocol breaks down);
more robust Position.setmp_thread_data, independently of Output.debugging (essentially reverts f9ec18f7c0f6, which was motivated by clean exception_trace, but without transaction positions the Isabelle_Process protocol breaks down);

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle