fix: never consider inert boundary effects

.changeset/healthy-hairs-run.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: never consider inert boundary effects

packages/svelte/src/internal/client/reactivity/effects.js

@@ -35,7 +35,8 @@ import {
 	INSPECT_EFFECT,
 	HEAD_EFFECT,
 	MAYBE_DIRTY,
-	EFFECT_HAS_DERIVED
+	EFFECT_HAS_DERIVED,
+	BOUNDARY_EFFECT
 } from '../constants.js';
 import { set } from './sources.js';
 import * as e from '../errors.js';
@@ -142,7 +143,7 @@ function create_effect(type, fn, sync, push = true) {
 		effect.first === null &&
 		effect.nodes_start === null &&
 		effect.teardown === null &&
-		(effect.f & EFFECT_HAS_DERIVED) === 0;
+		(effect.f & (EFFECT_HAS_DERIVED | BOUNDARY_EFFECT)) === 0;
 
 	if (!inert && !is_root && push) {
 		if (parent_effect !== null) {

packages/svelte/tests/runtime-runes/samples/error-boundary-21/Child.svelte

@@ -0,0 +1,3 @@
+<script>
+	throw new Error();
+</script>

packages/svelte/tests/runtime-runes/samples/error-boundary-21/_config.js

@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: '<button></button><div>0</div>',
+	mode: ['client'],
+	test({ assert, target }) {
+		let btn = target.querySelector('button');
+		let div = target.querySelector('div');
+
+		flushSync(() => {
+			btn?.click();
+		});
+
+		assert.equal(div?.innerHTML, `1`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/error-boundary-21/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	import Child from "./Child.svelte"
+
+	let count = $state(0);
+</script>
+
+<button onclick={()=>count++}></button>
+<svelte:boundary>
+	<Child />
+
+	{#snippet failed()}
+		<div>{count}</div>
+	{/snippet}
+</svelte:boundary>