fix: wrap implicit children into `renderer_snippet`

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js

@@ -1,7 +1,7 @@
 /** @import { BlockStatement, Expression, ExpressionStatement, Identifier, MemberExpression, Pattern, Property, SequenceExpression, SourceLocation, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../../types.js' */
-import { dev, is_ignored } from '../../../../../state.js';
+import { custom_renderer, dev, is_ignored } from '../../../../../state.js';
 import { get_attribute_chunks, object } from '../../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { add_svelte_meta, build_bind_this, Memoizer, validate_binding } from '../shared/utils.js';
@@ -391,13 +391,16 @@ export function build_component(node, component_name, loc, context) {
 						!node.attributes.some((attr) => attr.type === 'LetDirective')
 				)
 			) {
+				let children_fn = dev
+					? b.call('$.wrap_snippet', b.id(context.state.analysis.name), slot_fn)
+					: slot_fn;
+
+				if (custom_renderer) {
+					children_fn = b.call('$.renderer_snippet', b.id('$renderer'), children_fn);
+				}
+
 				// create `children` prop...
-				push_prop(
-					b.init(
-						'children',
-						dev ? b.call('$.wrap_snippet', b.id(context.state.analysis.name), slot_fn) : slot_fn
-					)
-				);
+				push_prop(b.init('children', children_fn));
 
 				// and `$$slots.default: true` so that `<slot>` on the child works
 				serialized_slots.push(b.init(slot_name, b.true));

packages/svelte/tests/custom-renderers/samples/single-node/Component.svelte

@@ -0,0 +1,5 @@
+<script lang="ts">
+	let { children } = $props();
+</script>
+
+{@render children?.()}

packages/svelte/tests/custom-renderers/samples/single-node/_config.js

@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	html: 'test'
+});

packages/svelte/tests/custom-renderers/samples/single-node/main.svelte

@@ -0,0 +1,5 @@
+<script>
+	import Component from "./Component.svelte";
+</script>
+
+<Component>test</Component>