Forward progress: questioning `weakly_parallel` guarantee of stream scheduler

We are wondering why the stream scheduler advertises its forward progress guarantee as weakly_parallel:

https://github.com/NVIDIA/stdexec/blob/e5dbe49a5257d29adee456f9f653acb00df634f5/include/nvexec/stream_context.cuh#L47-L49

Indeed, this page on the Cuda execution model,

https://nvidia.github.io/cccl/libcudacxx/extended_api/execution_model.html

mentions that

If the host implementation provides concurrent forward progress, then CUDA C++ provides parallel forward progress for device threads.

As potential reasons for the stream scheduler advertising only weakly_parallel, we have thought about the host implementation not necessarily providing concurrent forward progress and about the cuda architecture not necessarily providing independent thread scheduling prior to volta. But we are not sure. And so hence our question.

Also noting that we did see the same forward progress guarantee used in the new work in cudax.

Thanks in advance!

Joint work with @romintomasetti.

Start with include/nvexec/stream_context.cuh at lines 47-49 and read the linked CUDA execution model documentation, focusing on the conditions for parallel forward progress. Compare that explanation with the stream scheduler and the same guarantee in cudax. Done means the guarantee is clarified or the relevant documentation and declarations are updated.