fix: events don't go through propagation

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

@@ -63,10 +63,21 @@ export function replay_events(dom) {
  * @param {AddEventListenerOptions} [options]
  */
 export function create_event(event_name, dom, handler, options = {}) {
+	// Capture whether a custom renderer is active at creation time (during mount),
+	// since `renderer` will be null when the event actually fires
+	var is_custom_renderer = renderer != null;
+
 	/**
 	 * @this {EventTarget}
 	 */
 	function target_handler(/** @type {Event} */ event) {
+		if (is_custom_renderer) {
+			// Custom renderers don't use DOM event propagation/delegation,
+			// so just call the handler directly
+			return without_reactive_context(() => {
+				return handler?.call(this, event);
+			});
+		}
 		if (!options.capture) {
 			// Only call in the bubble phase, else delegated events would be called before the capturing events
 			handle_event_propagation.call(dom, event);

packages/svelte/tests/custom-renderers/samples/event-handler-no-propagation/_config.js

@@ -0,0 +1,24 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	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 a plain object that is NOT a DOM Event.
+		// If handle_event_propagation is called, it will fail because
+		// it tries to access DOM-specific properties like composedPath, ownerDocument, etc.
+		for (const { handler } of listeners) {
+			handler.call(button, { type: 'click' });
+		}
+		flushSync();
+
+		assert.deepEqual(logs, [{ type: 'click' }]);
+	}
+});

packages/svelte/tests/custom-renderers/samples/event-handler-no-propagation/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	function increment(e) {
+		console.log(e);
+	}
+</script>
+
+<button onclick={increment}>log</button>