diff --git a/.changeset/ninety-olives-report.md b/.changeset/ninety-olives-report.md
new file mode 100644
index 0000000000..3e66a41d02
--- /dev/null
+++ b/.changeset/ninety-olives-report.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: replace `undefined` with `void(0)` in CallExpressions
diff --git a/.changeset/wise-schools-report.md b/.changeset/wise-schools-report.md
new file mode 100644
index 0000000000..47ec887256
--- /dev/null
+++ b/.changeset/wise-schools-report.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: place store setup inside async body
diff --git a/documentation/docs/07-misc/04-custom-elements.md b/documentation/docs/07-misc/04-custom-elements.md
index 7e6a17b947..4e5afff7d2 100644
--- a/documentation/docs/07-misc/04-custom-elements.md
+++ b/documentation/docs/07-misc/04-custom-elements.md
@@ -4,7 +4,7 @@ title: Custom elements
 
 <!-- - [basically what we have today](https://svelte.dev/docs/custom-elements-api) -->
 
-Svelte components can also be compiled to custom elements (aka web components) using the `customElement: true` compiler option. You should specify a tag name for the component using the `<svelte:options>` [element](svelte-options).
+Svelte components can also be compiled to custom elements (aka web components) using the `customElement: true` compiler option. You should specify a tag name for the component using the `<svelte:options>` [element](svelte-options). Within the custom element you can access the host element via the [`$host`](https://svelte.dev/docs/svelte/$host) rune.
 
 ```svelte
 <svelte:options customElement="my-element" />
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index fb6b20c489..de94eb1897 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,31 @@
 # svelte
 
+## 5.38.6
+
+### Patch Changes
+
+- fix: don't fail on `flushSync` while flushing effects ([#16674](https://github.com/sveltejs/svelte/pull/16674))
+
+## 5.38.5
+
+### Patch Changes
+
+- fix: ensure async deriveds always get dependencies from thennable ([#16672](https://github.com/sveltejs/svelte/pull/16672))
+
+## 5.38.4
+
+### Patch Changes
+
+- fix: place instance-level snippets inside async body ([#16666](https://github.com/sveltejs/svelte/pull/16666))
+
+- fix: Add check for builtin custom elements in `set_custom_element_data` ([#16592](https://github.com/sveltejs/svelte/pull/16592))
+
+- fix: restore batch along with effect context ([#16668](https://github.com/sveltejs/svelte/pull/16668))
+
+- fix: wait until changes propagate before updating input selection state ([#16649](https://github.com/sveltejs/svelte/pull/16649))
+
+- fix: add "Accept-CH" as valid value for `http-equiv` ([#16671](https://github.com/sveltejs/svelte/pull/16671))
+
 ## 5.38.3
 
 ### Patch Changes
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index f63a31a96b..b0c2fae2de 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -1268,6 +1268,7 @@ export interface HTMLMetaAttributes extends HTMLAttributes<HTMLMetaElement> {
 	charset?: string | undefined | null;
 	content?: string | undefined | null;
 	'http-equiv'?:
+		| 'accept-ch'
 		| 'content-security-policy'
 		| 'content-type'
 		| 'default-style'
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index b7effe35bd..fe42603184 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.38.3",
+  "version": "5.38.6",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
index b7cfd30b7c..35f54a57cb 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js
@@ -362,22 +362,41 @@ export function client_component(analysis, options) {
 
 	let component_block = b.block([
 		store_init,
-		...store_setup,
 		...legacy_reactive_declarations,
-		...group_binding_declarations,
-		...state.instance_level_snippets
+		...group_binding_declarations
 	]);
 
+	const should_inject_context =
+		dev ||
+		analysis.needs_context ||
+		analysis.reactive_statements.size > 0 ||
+		component_returned_object.length > 0;
+
 	if (analysis.instance.has_await) {
+		if (should_inject_context && component_returned_object.length > 0) {
+			component_block.body.push(b.var('$$exports'));
+		}
 		const body = b.block([
+			...store_setup,
+			...state.instance_level_snippets,
 			.../** @type {ESTree.Statement[]} */ (instance.body),
+			...(should_inject_context && component_returned_object.length > 0
+				? [b.stmt(b.assignment('=', b.id('$$exports'), b.object(component_returned_object)))]
+				: []),
 			b.if(b.call('$.aborted'), b.return()),
 			.../** @type {ESTree.Statement[]} */ (template.body)
 		]);
 
 		component_block.body.push(b.stmt(b.call(`$.async_body`, b.arrow([], body, true))));
 	} else {
-		component_block.body.push(.../** @type {ESTree.Statement[]} */ (instance.body));
+		component_block.body.push(
+			...state.instance_level_snippets,
+			.../** @type {ESTree.Statement[]} */ (instance.body)
+		);
+		if (should_inject_context && component_returned_object.length > 0) {
+			component_block.body.push(b.var('$$exports', b.object(component_returned_object)));
+		}
+		component_block.body.unshift(...store_setup);
 
 		if (!analysis.runes && analysis.needs_context) {
 			component_block.body.push(b.stmt(b.call('$.init', analysis.immutable ? b.true : undefined)));
@@ -392,12 +411,6 @@ export function client_component(analysis, options) {
 		);
 	}
 
-	const should_inject_context =
-		dev ||
-		analysis.needs_context ||
-		analysis.reactive_statements.size > 0 ||
-		component_returned_object.length > 0;
-
 	let should_inject_props =
 		should_inject_context ||
 		analysis.needs_props ||
@@ -444,7 +457,7 @@ export function client_component(analysis, options) {
 		let to_push;
 
 		if (component_returned_object.length > 0) {
-			let pop_call = b.call('$.pop', b.object(component_returned_object));
+			let pop_call = b.call('$.pop', b.id('$$exports'));
 			to_push = needs_store_cleanup ? b.var('$$pop', pop_call) : b.return(pop_call);
 		} else {
 			to_push = b.stmt(b.call('$.pop'));
@@ -455,6 +468,7 @@ export function client_component(analysis, options) {
 
 	if (needs_store_cleanup) {
 		component_block.body.push(b.stmt(b.call('$$cleanup')));
+
 		if (component_returned_object.length > 0) {
 			component_block.body.push(b.return(b.id('$$pop')));
 		}
diff --git a/packages/svelte/src/compiler/utils/builders.js b/packages/svelte/src/compiler/utils/builders.js
index 56a5f31ffe..03a946ff9c 100644
--- a/packages/svelte/src/compiler/utils/builders.js
+++ b/packages/svelte/src/compiler/utils/builders.js
@@ -100,7 +100,7 @@ export function call(callee, ...args) {
 	if (typeof callee === 'string') callee = id(callee);
 	args = args.slice();
 
-	// replacing missing arguments with `undefined`, unless they're at the end in which case remove them
+	// replacing missing arguments with `void(0)`, unless they're at the end in which case remove them
 	let i = args.length;
 	let popping = true;
 	while (i--) {
@@ -108,7 +108,7 @@ export function call(callee, ...args) {
 			if (popping) {
 				args.pop();
 			} else {
-				args[i] = id('undefined');
+				args[i] = void0;
 			}
 		} else {
 			popping = false;
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 1866931ef2..60fe2b7d3c 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -1,10 +1,5 @@
 /** @import { Effect, Source, TemplateNode, } from '#client' */
-import {
-	BOUNDARY_EFFECT,
-	EFFECT_PRESERVED,
-	EFFECT_RAN,
-	EFFECT_TRANSPARENT
-} from '#client/constants';
+import { BOUNDARY_EFFECT, EFFECT_PRESERVED, EFFECT_TRANSPARENT } from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
 import { handle_error, invoke_error_boundary } from '../../error-handling.js';
 import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
diff --git a/packages/svelte/src/internal/client/dom/elements/attributes.js b/packages/svelte/src/internal/client/dom/elements/attributes.js
index 2fa5d4541c..a5b7140f25 100644
--- a/packages/svelte/src/internal/client/dom/elements/attributes.js
+++ b/packages/svelte/src/internal/client/dom/elements/attributes.js
@@ -238,10 +238,10 @@ export function set_custom_element_data(node, prop, value) {
 			// Don't compute setters for custom elements while they aren't registered yet,
 			// because during their upgrade/instantiation they might add more setters.
 			// Instead, fall back to a simple "an object, then set as property" heuristic.
-			(setters_cache.has(node.nodeName) ||
+			(setters_cache.has(node.getAttribute('is') || node.nodeName) ||
 			// customElements may not be available in browser extension contexts
 			!customElements ||
-			customElements.get(node.tagName.toLowerCase())
+			customElements.get(node.getAttribute('is') || node.tagName.toLowerCase())
 				? get_setters(node).includes(prop)
 				: value && typeof value === 'object')
 		) {
@@ -546,9 +546,10 @@ var setters_cache = new Map();
 
 /** @param {Element} element */
 function get_setters(element) {
-	var setters = setters_cache.get(element.nodeName);
+	var cache_key = element.getAttribute('is') || element.nodeName;
+	var setters = setters_cache.get(cache_key);
 	if (setters) return setters;
-	setters_cache.set(element.nodeName, (setters = []));
+	setters_cache.set(cache_key, (setters = []));
 
 	var descriptors;
 	var proto = element; // In the case of custom elements there might be setters on the instance
diff --git a/packages/svelte/src/internal/client/dom/elements/bindings/input.js b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
index 67e6ff1dd2..815acde7c5 100644
--- a/packages/svelte/src/internal/client/dom/elements/bindings/input.js
+++ b/packages/svelte/src/internal/client/dom/elements/bindings/input.js
@@ -6,7 +6,7 @@ import * as e from '../../../errors.js';
 import { is } from '../../../proxy.js';
 import { queue_micro_task } from '../../task.js';
 import { hydrating } from '../../hydration.js';
-import { untrack } from '../../../runtime.js';
+import { tick, untrack } from '../../../runtime.js';
 import { is_runes } from '../../../context.js';
 import { current_batch, previous_batch } from '../../../reactivity/batch.js';
 
@@ -17,11 +17,9 @@ import { current_batch, previous_batch } from '../../../reactivity/batch.js';
  * @returns {void}
  */
 export function bind_value(input, get, set = get) {
-	var runes = is_runes();
-
 	var batches = new WeakSet();
 
-	listen_to_event_and_reset_event(input, 'input', (is_reset) => {
+	listen_to_event_and_reset_event(input, 'input', async (is_reset) => {
 		if (DEV && input.type === 'checkbox') {
 			// TODO should this happen in prod too?
 			e.bind_invalid_checkbox_value();
@@ -36,9 +34,13 @@ export function bind_value(input, get, set = get) {
 			batches.add(current_batch);
 		}
 
-		// In runes mode, respect any validation in accessors (doesn't apply in legacy mode,
-		// because we use mutable state which ensures the render effect always runs)
-		if (runes && value !== (value = get())) {
+		// Because `{#each ...}` blocks work by updating sources inside the flush,
+		// we need to wait a tick before checking to see if we should forcibly
+		// update the input and reset the selection state
+		await tick();
+
+		// Respect any validation in accessors
+		if (value !== (value = get())) {
 			var start = input.selectionStart;
 			var end = input.selectionEnd;
 
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
index 0b404920b8..6dc1dce543 100644
--- a/packages/svelte/src/internal/client/reactivity/async.js
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -73,11 +73,13 @@ function capture() {
 	var previous_effect = active_effect;
 	var previous_reaction = active_reaction;
 	var previous_component_context = component_context;
+	var previous_batch = current_batch;
 
 	return function restore() {
 		set_active_effect(previous_effect);
 		set_active_reaction(previous_reaction);
 		set_component_context(previous_component_context);
+		previous_batch?.activate();
 
 		if (DEV) {
 			set_from_async_derived(null);
@@ -176,8 +178,8 @@ export function unset_context() {
  * @param {() => Promise<void>} fn
  */
 export async function async_body(fn) {
-	const unsuspend = suspend();
-	const active = /** @type {Effect} */ (active_effect);
+	var unsuspend = suspend();
+	var active = /** @type {Effect} */ (active_effect);
 
 	try {
 		await fn();
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 60fa03c56c..82f1de67a9 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -76,8 +76,8 @@ let queued_root_effects = [];
 let last_scheduled_effect = null;
 
 let is_flushing = false;
-
 let is_flushing_sync = false;
+
 export class Batch {
 	/**
 	 * The current values of any sources that are updated in this batch
@@ -187,7 +187,7 @@ export class Batch {
 		// if there are multiple batches, we are 'time travelling' —
 		// we need to undo the changes belonging to any batch
 		// other than the current one
-		if (batches.size > 1) {
+		if (async_mode_flag && batches.size > 1) {
 			current_values = new Map();
 			batch_deriveds = new Map();
 
@@ -484,6 +484,7 @@ export class Batch {
  */
 export function flushSync(fn) {
 	if (async_mode_flag && active_effect !== null) {
+		// We disallow this because it creates super-hard to reason about stack trace and because it's generally a bad idea
 		e.flush_sync_in_effect();
 	}
 
@@ -622,7 +623,9 @@ function flush_queued_effects(effects) {
 				}
 			}
 
-			if (eager_block_effects.length > 0) {
+			// If update_effect() has a flushSync() in it, we may have flushed another flush_queued_effects(),
+			// which already handled this logic and did set eager_block_effects to null.
+			if (eager_block_effects?.length > 0) {
 				// TODO this feels incorrect! it gets the tests passing
 				old_values.clear();
 
@@ -678,6 +681,8 @@ export function suspend() {
 		if (!pending) {
 			batch.activate();
 			batch.decrement();
+		} else {
+			batch.deactivate();
 		}
 
 		unset_context();
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index 7f730e365e..31dc267960 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -120,6 +120,9 @@ export function async_derived(fn, location) {
 
 		try {
 			var p = fn();
+			// Make sure to always access the then property to read any signals
+			// it might access, so that we track them as dependencies.
+			if (prev) Promise.resolve(p).catch(() => {}); // avoid unhandled rejection
 		} catch (error) {
 			p = Promise.reject(error);
 		}
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 815b25bf1f..67c586790f 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.38.3';
+export const VERSION = '5.38.6';
 export const PUBLIC_VERSION = '5';
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-reverse-order/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-reverse-order/_config.js
new file mode 100644
index 0000000000..bd0dd753c2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-reverse-order/_config.js
@@ -0,0 +1,41 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [increment, pop] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+
+		pop.click();
+		await tick();
+
+		pop.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>pop</button>
+				<p>1</p>
+			`
+		);
+
+		increment.click();
+		await tick();
+
+		pop.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>pop</button>
+				<p>2</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-reverse-order/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-reverse-order/main.svelte
new file mode 100644
index 0000000000..b9f6c26c2a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-reverse-order/main.svelte
@@ -0,0 +1,35 @@
+
+<script>
+	let count = $state(0);
+
+	let deferreds = [];
+
+	class X {
+		constructor(promise) {
+			this.promise = promise;
+		}
+		
+		get then() {
+			count;
+
+			return (resolve) => this.promise.then(() => count).then(resolve)
+		}
+	}
+
+	function push() {
+		const deferred = Promise.withResolvers();
+		deferreds.push(deferred);
+		return new X(deferred.promise);
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => deferreds.pop()?.resolve(count)}>pop</button>
+
+<svelte:boundary>
+	<p>{await push()}</p>
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/Bar.svelte b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/Bar.svelte
new file mode 100644
index 0000000000..f1ac9ab760
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/Bar.svelte
@@ -0,0 +1,7 @@
+<script lang="ts">
+	import { resolve } from './main.svelte';
+
+	const bar = await new Promise((r) => resolve.push(() => r('bar')));
+</script>
+
+<p>bar: {bar}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/Foo.svelte b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/Foo.svelte
new file mode 100644
index 0000000000..e2029a3033
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/Foo.svelte
@@ -0,0 +1,10 @@
+<script lang="ts">
+	import { resolve } from './main.svelte';
+	import Bar from './Bar.svelte';
+
+	const foo = await new Promise((r) => resolve.push(() => r('foo')));
+</script>
+
+<p>foo: {foo}</p>
+
+<Bar/>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/_config.js b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/_config.js
new file mode 100644
index 0000000000..ca7965bf79
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/_config.js
@@ -0,0 +1,42 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [show, resolve] = target.querySelectorAll('button');
+
+		show.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>show</button>
+				<button>resolve</button>
+				<p>pending...</p>
+			`
+		);
+
+		resolve.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>show</button>
+				<button>resolve</button>
+				<p>pending...</p>
+			`
+		);
+
+		resolve.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>show</button>
+				<button>resolve</button>
+				<p>foo: foo</p>
+				<p>bar: bar</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/main.svelte
new file mode 100644
index 0000000000..bd0efaa4f8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-nested-top-level/main.svelte
@@ -0,0 +1,31 @@
+<script module>
+	export let resolve = [];
+</script>
+
+<script>
+	import Foo from './Foo.svelte';
+	
+	let show = $state(false);
+</script>
+
+<button onclick={() => show = true}>
+	show
+</button>
+
+<button onclick={() => resolve.shift()()}>
+	resolve
+</button>
+
+<svelte:boundary>
+	{#if show}
+		<Foo/>
+	{/if}
+
+	{#if $effect.pending()}
+		<p>pending...</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>initializing...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js b/packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js
index ebbe642860..fe92977c21 100644
--- a/packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/async-redirect/_config.js
@@ -29,6 +29,7 @@ export default test({
 				<button>c</button>
 				<button>ok</button>
 				<p>c</p>
+				<p>b or c</p>
 			`
 		);
 
@@ -46,6 +47,7 @@ export default test({
 				<button>c</button>
 				<button>ok</button>
 				<p>b</p>
+				<p>b or c</p>
 			`
 		);
 	}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte
index bf5fdf9ed3..aead1b00e5 100644
--- a/packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/async-redirect/main.svelte
@@ -33,6 +33,10 @@
 		<p>c</p>
 	{/if}
 
+	{#if route === 'b' || route === 'c'}
+		<p>b or c</p>
+	{/if}
+
 	{#snippet pending()}
 		<p>pending...</p>
 	{/snippet}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/_config.js b/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/_config.js
new file mode 100644
index 0000000000..c6903c3eed
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/_config.js
@@ -0,0 +1,9 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, 'value');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/app.svelte b/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/app.svelte
new file mode 100644
index 0000000000..27b29cfe50
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/app.svelte
@@ -0,0 +1,9 @@
+<script>
+	const value = await 'value';
+</script>
+
+{#snippet valueSnippet()}
+	{value}
+{/snippet}
+
+{@render valueSnippet()}
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/main.svelte
new file mode 100644
index 0000000000..c251a5645b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-reference-in-snippet/main.svelte
@@ -0,0 +1,8 @@
+<script>
+    import App from './app.svelte';
+</script>
+<svelte:boundary>
+    {#snippet pending()}
+    {/snippet}
+    <App />
+</svelte:boundary>
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/Foo.svelte b/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/Foo.svelte
new file mode 100644
index 0000000000..e8a7c84137
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/Foo.svelte
@@ -0,0 +1,8 @@
+<script lang="ts">
+	import { resolve } from './main.svelte';
+
+	const foo = $derived(await new Promise((r) => resolve.push(() => r('foo'))));
+	const bar = $derived(await new Promise((r) => resolve.push(() => r('bar'))));
+</script>
+
+<p>{foo} {bar}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/_config.js b/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/_config.js
new file mode 100644
index 0000000000..2c7ffd3952
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/_config.js
@@ -0,0 +1,41 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [show, resolve] = target.querySelectorAll('button');
+
+		show.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>show</button>
+				<button>resolve</button>
+				<p>pending...</p>
+			`
+		);
+
+		resolve.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>show</button>
+				<button>resolve</button>
+				<p>pending...</p>
+			`
+		);
+
+		resolve.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>show</button>
+				<button>resolve</button>
+				<p>foo bar</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/main.svelte
new file mode 100644
index 0000000000..bd0efaa4f8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-top-level-deriveds/main.svelte
@@ -0,0 +1,31 @@
+<script module>
+	export let resolve = [];
+</script>
+
+<script>
+	import Foo from './Foo.svelte';
+	
+	let show = $state(false);
+</script>
+
+<button onclick={() => show = true}>
+	show
+</button>
+
+<button onclick={() => resolve.shift()()}>
+	resolve
+</button>
+
+<svelte:boundary>
+	{#if show}
+		<Foo/>
+	{/if}
+
+	{#if $effect.pending()}
+		<p>pending...</p>
+	{/if}
+
+	{#snippet pending()}
+		<p>initializing...</p>
+	{/snippet}
+</svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-in-each/_config.js b/packages/svelte/tests/runtime-runes/samples/binding-update-in-each/_config.js
new file mode 100644
index 0000000000..b6371ce11c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-in-each/_config.js
@@ -0,0 +1,28 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+
+	html: `<input><p>a</a>`,
+
+	async test({ assert, target }) {
+		const [input] = target.querySelectorAll('input');
+
+		input.focus();
+		input.value = 'ab';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, `<input><p>ab</a>`);
+		assert.equal(input.value, 'ab');
+
+		input.focus();
+		input.value = 'abc';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, `<input><p>abc</a>`);
+		assert.equal(input.value, 'abc');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-in-each/main.svelte b/packages/svelte/tests/runtime-runes/samples/binding-update-in-each/main.svelte
new file mode 100644
index 0000000000..7925195ee1
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-in-each/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	let array = $state([{ value: 'a' }]);
+</script>
+
+{#each array as obj}
+	<input bind:value={() => obj.value, (value) => array = [{ value }]} />
+	<p>{obj.value}</p>
+{/each}
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-3/_config.js b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-3/_config.js
new file mode 100644
index 0000000000..0909dee7a8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-3/_config.js
@@ -0,0 +1,30 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+
+	async test({ assert, target }) {
+		const [input] = target.querySelectorAll('input');
+
+		input.focus();
+		input.value = 'Ab';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+
+		await tick();
+		await tick();
+
+		assert.equal(input.value, 'AB');
+		assert.htmlEqual(target.innerHTML, `<input /><p>AB</p>`);
+
+		input.focus();
+		input.value = 'ABc';
+		input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+
+		await tick();
+		await tick();
+
+		assert.equal(input.value, 'ABC');
+		assert.htmlEqual(target.innerHTML, `<input /><p>ABC</p>`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-3/main.svelte b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-3/main.svelte
new file mode 100644
index 0000000000..b61bfe4e67
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/binding-update-while-focused-3/main.svelte
@@ -0,0 +1,6 @@
+<script>
+	let text = $state('A');
+</script>
+
+<input bind:value={() => text, (v) => text = v.toUpperCase()} />
+<p>{text}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/_config.js b/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/_config.js
index 7f406d8f0d..3d8917c147 100644
--- a/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/_config.js
@@ -20,5 +20,8 @@ export default test({
 		const [value1, value2] = target.querySelectorAll('value-element');
 		assert.equal(value1.shadowRoot?.innerHTML, '<span>test</span>');
 		assert.equal(value2.shadowRoot?.innerHTML, '<span>test</span>');
+
+		const value_builtin = target.querySelector('div');
+		assert.equal(value_builtin?.shadowRoot?.innerHTML, '<span>test</span>');
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/main.svelte b/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/main.svelte
index 82774f160d..badb8f96c7 100644
--- a/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/custom-element-attributes/main.svelte
@@ -15,6 +15,24 @@
 			}
 		});
 	}
+	if(!customElements.get('value-builtin')) {
+		customElements.define('value-builtin', class extends HTMLDivElement {
+
+			constructor() {
+				super();
+				this.attachShadow({ mode: 'open' });
+			}
+
+			set value(v) {
+				if (this.__value !== v) {
+					this.__value = v;
+					this.shadowRoot.innerHTML = `<span>${v}</span>`;
+				}
+			}
+		}, {
+			extends: 'div'
+		});
+	}
 </script>
 
 <my-element string="test" object={{ test: true }}></my-element>
@@ -22,3 +40,4 @@
 
 <value-element value="test"></value-element>
 <value-element {...{value: "test"}}></value-element>
+<div is="value-builtin" value="test"></div>
diff --git a/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/Child.svelte b/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/Child.svelte
new file mode 100644
index 0000000000..44447e4f36
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/Child.svelte
@@ -0,0 +1,7 @@
+<script>
+    let { text } = $props();
+
+    $effect(() => console.log(text));
+</script>
+
+{text}
diff --git a/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/_config.js b/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/_config.js
new file mode 100644
index 0000000000..ec8858b2c6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/_config.js
@@ -0,0 +1,12 @@
+import { async_mode } from '../../../helpers';
+import { test } from '../../test';
+
+export default test({
+	// In legacy mode this succeeds and logs 'hello'
+	// In async mode this throws an error because flushSync is called inside an effect
+	async test({ assert, target, logs }) {
+		assert.htmlEqual(target.innerHTML, `<button>show</button> <div>hello</div>`);
+		assert.deepEqual(logs, ['hello']);
+	},
+	runtime_error: async_mode ? 'flush_sync_in_effect' : undefined
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/main.svelte b/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/main.svelte
new file mode 100644
index 0000000000..bef820376b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/flush-sync-inside-attachment/main.svelte
@@ -0,0 +1,13 @@
+<script>
+	import { flushSync, mount } from 'svelte'
+	import Child from './Child.svelte';
+
+	let show = $state(false);
+</script>
+
+<button onclick={() => show = true}>show</button>
+
+<div {@attach (target) => {
+	mount(Child, { target, props: { text: 'hello' }  });
+	flushSync();
+}}></div>