I think what you are describing looks a lot like what the Svelte team is trying to achieve with the reactive assignments "$:" A couple years ago, that feature

I think what you are describing looks a lot like what the Svelte team is trying to achieve with the reactive assignments "$:" A couple years ago, that feature used to work similar as useEffect, so I got used to use it for transitions, and now is biting my ass because the Svelte team are breaking my transition use-cases