you could tack the seams back together and embroider a band-aid over it?

mhh.
Either a parachute stitch (but given that there stitching already on one edge it might be unpleasant to do) or a canvas patch (preferably both inside and outside) and running stitch embroidery to keep them in place. Colours and designs of your choice.

duct tape fixes everything 😃

@CrazyDogLadysezPEACE @Saule, anar en Mousses I like the parachute stitch idea, but I don't know how it'll work being so close to the seam.

@heartofcoyote yup. Same. Technically it could work just... ehh. The patch is probably the best option here.

@PeryleneBleu @heartofcoyote not very good. To do it right I think you'd unpick the seams towards the cuff, cut the panel off a thumb's width above the tear around the sleeve and replace it completely.

@PalmAndNeedle Me, I'd unpick the double line of stitches off the cuff, trim away any of the torn fabric from the edge of the sleeve, sew a patch onto the frayed bit of sleeve, tuck those back under the cuff, and topstitch the cuff back on.
Any of this could be done with fun contrasting colours, by hand or by machine!

@Sini Tuulia @PalmAndNeedle Yeah, that's the route I'm currently leaning.

@sinituulia there we go, I didn't picture the construction of this correctly. Sounds like a good plan