Actually a windshirt meets most of those needs. Depends on how long you want for it to keep you dry.

Softshells and such are bulky. Event material is about the best waterproof available but is expensive and again probably a bit bulky as something to stow away as emergency gear.

I use a windshirt from montane. Just do a search for Montane Featherlight gear. My jacket weighs 4 grams, packs as small as an orange so can be perfect for emegency gear. It'll only keep you dry in a light rain for about an hour. If your working hard you'll keep evaporating it out about as fast though.