Add regression test for #13358

Closes phpstan/phpstan#13358

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

tests/PHPStan/Analyser/nsrt/bug-13358.php

@@ -0,0 +1,45 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13358;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @phpstan-sealed SystemActor|AnonymousVisitorActor
+ */
+abstract class Actor
+{
+	/**
+	 * @phpstan-assert-if-true SystemActor $this
+	 */
+	public function isSystem() : bool
+	{
+		return $this instanceof SystemActor;
+	}
+
+	/**
+	 * @phpstan-assert-if-true AnonymousVisitorActor $this
+	 */
+	public function isAnonymousVisitor() : bool
+	{
+		return $this instanceof AnonymousVisitorActor;
+	}
+}
+
+class SystemActor extends Actor
+{
+}
+
+class AnonymousVisitorActor extends Actor
+{
+}
+
+function (AnonymousVisitorActor|SystemActor $actor): void {
+	assertType('Bug13358\AnonymousVisitorActor|Bug13358\SystemActor', $actor);
+
+	if ($actor->isSystem()) {
+		assertType('Bug13358\SystemActor', $actor);
+	} else {
+		assertType('Bug13358\AnonymousVisitorActor', $actor);
+	}
+};