Describe the bug

Honestly, the code explains the edge-case better than words:

<script>	
	let index = $state(0);

	function fn(id) {
		// When index changes to from 0 to 1, we explicitly simulate the undefined error
		if (id === 2) throw new Error("Simulated TypeError");
	}
</script>

<button onclick={() => index = 1}>Trigger</button>

<svelte:boundary>
	{#snippet pending()}Loading...{/snippet}
	{#snippet failed(error)}Error Caught: {error.message}{/snippet}

	{#each [[1], [2]][index] as id (id)}
		{@const result = await fn(id)}
	{/each}
</svelte:boundary>

The result isn't even used, and fn isn't actually doing any async work, but the console will still log this cryptic error: TypeError: Cannot read properties of undefined (reading 'e') instead of the real error that was actually thrown.

It requires the error boundary to log (not 100% if that's just in the playground environment) and behaviour does not change by removing the pending snippet.

Also, I'm pretty sure that a $state mutation IS required for this to happen.

Reproduction

Logs

TypeError: Cannot read properties of undefined (reading 'e')
    at reconcile (playground:output:5781:54)
    at commit (playground:output:5604:4)
    at Batch.flush (playground:output:1248:46)
    at Batch.revive (playground:output:1390:9)
    at Array.eval (playground:output:1369:11)
    at run_all (playground:output:126:10)
    at run_micro_tasks (playground:output:752:3)
    at eval (playground:output:770:32)

System Info

playground with svelte `5.53.6`

Severity

annoyance