As above, cove prior to mist coating the wall. Coving can be a little messy, you’ve got adhesive squishing out from cove edges, (use this to fill any gaps as you clean up), the odd blob dropping onto wall, and sanding down after filling where you’ve got corners and joints along the lengths
All this will make a mess of your mist coat so best to get the messy work out of the way first
Have to disagree with Jord above with using tile adhesive - in my diy experience, tile adhesive on plaster surfaces can affect the paint finish, even with clearing away excess adhesive and wiping down
Powdered Cove adhesive would be my choice, around £12 for 5kg (wickes) goes a long way, easy to work with and clean off excess, can also use to fill gaps / joints / and sand down for a perfect finish