So I was in the process of hanging drywall in a room in our house, as part of a renovation project (we had to fix a large 4 ft by 2 ft patch). I was in the middle of laminating coats of compound over the joints when I had to leave the house for a couple weeks. To help keep things moving, we asked someone to paint the room our new eggshell color, but avoid the large wall patch area. Well we got back and they painted over my partially finished taping job, despite my specific request they not do so. It's pretty unsightly. Ugh. What should I do? Should I try to sand off the eggshell paint and finish taping? Or should I scuff up the wall with a sanding block and compound over the paint, seal it, and then paint again?
Joint compound will stick to paint with an eggshell sheen just fine.
I am guessing they didn't paint the fresh patch with a PVA primer so the mud on the wall hasn't even been sealed yet. Unless they put a lot coats of topcoat pain over the patch in which case they could of sealed it up with the more expensive paint. But, regardless you can move forward just fine.
To get the new patch though to blend in and not show up later, make sure you use a PVA or similar primer, they even sell some special paint for fresh drywall sealing (which is just a PVA primer anyway with a fancier name). If you don't seal it with a primer, the patch and existing painted surfaces will each take the paint differently and still show. PVA primer is sandable so you can take the primer out onto the wall a bit and sand your patch edges thinner without it peeling up. The PVA will kind glue the thin compound together and bond it to the wall, especially so if you are using a "lite" topping compound.