fix: ensure `$$slots` exists in runes mode (#9718)

fixes #9683

.changeset/flat-melons-protect.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure `$$slots` exists in runes mode

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -892,6 +892,11 @@ const common_visitors = {
 		const parent = /** @type {import('estree').Node} */ (context.path.at(-1));
 		if (!is_reference(node, parent)) return;
 
+		if (node.name === '$$slots') {
+			context.state.analysis.uses_slots = true;
+			return;
+		}
+
 		const binding = context.state.scope.get(node.name);
 
 		// if no binding, means some global variable

packages/svelte/tests/runtime-runes/samples/slot/_config.js

@@ -0,0 +1,6 @@
+import { test } from '../../test';
+
+// Test that $$slots exists in runes mode
+export default test({
+	html: `<p>bar</p>`
+});

packages/svelte/tests/runtime-runes/samples/slot/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	import Slot from './slot.svelte';
+</script>
+
+<Slot>
+	<p>bar</p>
+</Slot>

packages/svelte/tests/runtime-runes/samples/slot/slot.svelte

@@ -0,0 +1,3 @@
+{#if $$slots}
+	<slot></slot>
+{/if}