+1 for prompts as depicted by The Composer.

I wonder how the Portent ability would work under that system.

Portent is an ability granted to 2nd level wizards in the divination school of magic. At the start of every day, they roll 2 d20s and record the results. They can then use those results on anyone they can see making an attack roll, saving throw or ability check. The target uses the recorded d20 roll instead of rolling themselves.
I’m all for maximum control over reactive abilities (though this one doesn’t technically use a reaction) but Portent would trigger a prompt any time anyone does anything. Is this ability in Solasta? How does it work there?