Appreciate the response! You're right on Svelte v5; I just confirmed that Svelte's new runes are indeed reactive:

    let count = $state(0);
    
    function increment() {
      count += 1;
      console.log(count + " + 1 = " + countPlusOne);  // prints "1 + 1 = 2"
     }

    let countPlusOne = $derived(count + 1);