The previous owner of a recumbent trike I'm renovating had cut a slice off both the upright seat frame tubes. With additional scrapes around top of each tube I'd surmise it was done to avoid the need to remove the seat when moving the trike from the back to the front of his terrace house.
Whilst that may well have eased movement through his back passage (sorry for that one), it does mean the top of the mesh seat covering can't be correctly tensioned.
Using metal bonding resin as glue, two support tubes were inserted to an appropriate depth first, then a correctly-sized and shaped "crown" was bonded onto the support on each side.
File/sand to flush, now the frame is ready for some paint.