fix: properly hydrate await in `{@html}`

.changeset/bright-pants-send.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: properly hydrate await in `{@html}`

packages/svelte/src/internal/client/dom/blocks/async.js

@@ -1,4 +1,6 @@
 /** @import { Blocker, TemplateNode, Value } from '#client' */
+import { COMMENT_NODE } from '#client/constants';
+import { HYDRATION_START, HYDRATION_START_ELSE } from '../../../../constants.js';
 import { flatten } from '../../reactivity/async.js';
 import { Batch, current_batch } from '../../reactivity/batch.js';
 import { get } from '../../runtime.js';
@@ -34,10 +36,17 @@ export function async(node, blockers = [], expressions = [], fn) {
 	var was_hydrating = hydrating;
 
 	if (was_hydrating) {
+		// Check if this is an `@html` block by looking at the current comment
+		// `@html` uses a hash comment (not `[` or `[!`) with empty comment as end marker
+		var is_html =
+			hydrate_node.nodeType === COMMENT_NODE &&
+			/** @type {Comment} */ (hydrate_node).data !== HYDRATION_START &&
+			/** @type {Comment} */ (hydrate_node).data !== HYDRATION_START_ELSE;
+
 		hydrate_next();
 
 		var previous_hydrate_node = hydrate_node;
-		var end = skip_nodes(false);
+		var end = skip_nodes(false, is_html);
 		set_hydrate_node(end);
 	}
 

packages/svelte/src/internal/client/dom/hydration.js

@@ -83,8 +83,9 @@ export function next(count = 1) {
 /**
  * Skips or removes (depending on {@link remove}) all nodes starting at `hydrate_node` up until the next hydration end comment
  * @param {boolean} remove
+ * @param {boolean} [is_html] - If true, look for empty comment end marker (used by `@html` blocks)
  */
-export function skip_nodes(remove = true) {
+export function skip_nodes(remove = true, is_html = false) {
 	var depth = 0;
 	var node = hydrate_node;
 
@@ -97,6 +98,9 @@ export function skip_nodes(remove = true) {
 				depth -= 1;
 			} else if (data === HYDRATION_START || data === HYDRATION_START_ELSE) {
 				depth += 1;
+			} else if (is_html && data === '' && depth === 0) {
+				// `@html` blocks use an empty comment as end marker
+				return node;
 			}
 		}
 

packages/svelte/tests/runtime-runes/samples/await-html-hydration/_config.js

@@ -0,0 +1,6 @@
+import { test } from '../../test';
+
+export default test({
+	mode: ['hydrate'],
+	async test() {}
+});

packages/svelte/tests/runtime-runes/samples/await-html-hydration/main.svelte

@@ -0,0 +1 @@
+<div>{@html await Promise.resolve(`<span>Foo</span>`)}</div>