await_waterfall suggested fix does not work due to lazy evaluation

[RuthgerD]

Describe the bug

According to:
https://svelte.dev/docs/svelte/runtime-warnings#Client-warnings-await_waterfall

You can start concurrent promises by creating them prior to awaiting them, on paper this seems fine however $derived values are lazy meaning it can't really work conceptually:

let aPromise = $derived(one());
let bPromise = $derived(two());

// at this point one() and two() have not been called yet

let a = $derived(await aPromise); // aPromise is evaluated, one() is called (async derived is eager)
let b = $derived(await bPromise); // bPromise is only evaluated once `a` is done

forcing evaluation of the derived values "fixes this" (e.g $inspect(aPromise, bPromise)), but that is a bit dumb.

What is the expected behavior here?

Reproduction

https://svelte.dev/playground/d3a249ca4fd44e24b6f83e66375cbc22?version=5.36.13

Severity

annoyance

[sillvva]

Also, when navigating to a page that has this await_waterfall issue, I've noticed that an error like this may occur:

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'increment')

Under async_effect

    if (should_suspend) {
      boundary2.update_pending_count(1);
      if (!pending2) batch.increment();
    }

It only happens when navigating to a page that has multiple query functions, awaited or not.