fix: event listeners in spread

packages/svelte/src/internal/client/dom/elements/attributes.js

@@ -395,7 +395,7 @@ function set_attributes(
 			const opts = {};
 			const event_handle_key = '$$' + key;
 			let event_name = key.slice(2);
-			var is_delegated = can_delegate_event(event_name);
+			var is_delegated = renderer == null && can_delegate_event(event_name);
 
 			if (is_capture_event(event_name)) {
 				event_name = event_name.slice(0, -7);
@@ -419,10 +419,10 @@ function set_attributes(
 			} else if (value != null) {
 				/**
 				 * @this {any}
-				 * @param {Event} evt
+				 * @param {...any} args
 				 */
-				function handle(evt) {
+				function handle(...args) {
-					current[key].call(this, evt);
+					current[key].apply(this, args);
 				}
 
 				current[event_handle_key] = create_event(event_name, element, handle, opts);

packages/svelte/tests/custom-renderers/samples/event-handler-spread/_config.js

@@ -0,0 +1,29 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: '<button>click me</button> <p>0</p>',
+	test({ assert, target, serialize, logs }) {
+		const button = target.children.find(
+			(/** @type {any} */ n) => n.type === 'element' && n.name === 'button'
+		);
+		assert.ok(button);
+
+		const listeners = button.listeners?.click;
+		assert.ok(listeners, 'button should have click listeners');
+
+		// Call the handler with multiple arguments.
+		// Custom renderers may pass multiple arguments to event handlers,
+		// so we need to make sure all arguments are forwarded through spreads too.
+		for (const { handler } of listeners) {
+			handler.call(button, { type: 'click' }, 'extra', 42);
+		}
+		flushSync();
+
+		const html = serialize(target);
+		assert.equal(html, '<button>click me</button> <p>1</p>');
+
+		// Verify all arguments were forwarded to the actual handler
+		assert.deepEqual(logs, [{ type: 'click' }, 'extra', 42]);
+	}
+});

packages/svelte/tests/custom-renderers/samples/event-handler-spread/main.svelte

@@ -0,0 +1,13 @@
+<script>
+	let count = $state(0);
+
+	const spread = {
+		onclick(...args) {
+			count++;
+			console.log(...args);
+		}
+	};
+</script>
+
+<button {...spread}>click me</button>
+<p>{count}</p>