I'd like to write a plugin to do x but there is no hook for it

[xoft]

OnEntityAddEffect is only fired for when the effect is added to the player (start the countdown, add particles etc.) There's no exact hook that is fired when the effect is actually being carried out. Good point on pointing that out, even non-players can gain health from potions, so we might want to consider the OnEntityHealthRegeneration hook, that would be fired for all instances of an entity gaining health, with a parameter telling what the source of the regeneration is - whether it's food-based, or potion-based. Can we think of any other source?