Final update - as suggested I did redo the job, and used a new filter from the dealer. Nothing got knocked loose or some other random mistake.
All signs point to the pump. Pulled the lines to the cooler and gave it quick start, expecting fluid to spray everywhere ... not a drop.
Therefore my only conclusion is pump shaft, unless anyone else can offer an easy possibility for why the pump may have spontaneously stopped working.
Thanks for all the advice.