Async component initialization crashes when current_batch is null

Describe the bug

I've been getting random Uncaught TypeError: can't access property "increment", batch is null errors, I have no idea how that happens, my best guess is that an async component was mounted or destroyed while another update was still being processed, I can’t confirm the exact action that caused it so I tried to slop distill a reproduction and codex found a reproduction that reliably gets me the same error. My app extensively uses mount api to launch modals that use async inside so that can be related somehow.

Reproduction

This fails on Svelte 5.57.0, #18558, and #18726.

<!-- Child.svelte -->

<script>
  const value = $derived(await Promise.resolve('child'));
</script>

<p data-child>{value}</p>

<!-- Main.svelte -->
<script>
  import Child from './Child.svelte';

  let anchor;
  let run = $state(false);

  $effect(() => {
  	if (run && anchor) Child(anchor, {});
  });
</script>

<button onclick={() => (run = !run)}>run</button>
<span bind:this={anchor}></span>

Logs

Uncaught TypeError: can't access property "increment", batch is null

  in $effect
  in App.svelte
  in __wrapper.svelte
  in undefined

System Info

N/A

Severity

annoyance