I managed to cut the tenons pretty close to the stool, but I had a devil of a time getting the stubs to be flush with the seat; I also really messed up the surface finish of the seat in the process with scratches and digs from the saw and, later, the handplane.
The stool seat is hard maple, and the legs are ash - it's my first time working with ash and I found the end-grain very difficult to plane or pare with any degree of control.
The spelching you can see here was really disheartening - it happened at the end of a paring cut with the chisel. However, I got similar results with the plane (but not as severe, since the tenon-stubs were taller when I was trying the plane).
I'm relatively sure sharpness isn't at issue; I sharpened my plane iron and the chisel right before trying this (I knew planing endgrain was a pain) to the extent they were both able to take hairs off my arm.
I know from the Paul Sellers video that too-tall tenon stubs are quite tricky, so I'm sure this was part of my issue, although I don't see how I could cut any closer to the seat without completely marring the surface.
Eventually I gave up and flattened the last bits with a sandpaper-block, even though I was trying to avoid using any abrasives and achieve an OK finish with the plane. However, the sandpaper (400 grit) scuffed up the maple figure and I had to do a finishing pass with the plane afterwards. (This was its own challenge, probably best for another question though).
So my question is, what should I have done here? How do I trim the tenons so they are flush without messing up the surface of the seat? Alternately, if it's a foregone conclusion that the seat will be marred, how do I plane it so I'm not catching on the tenon-grain as I'm planing with the seat-grain?
Thanks for any help you can provide!