Document how the bug-12972b e2e autoloader reproduces the issue

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: phpstan-bot

e2e/bug-12972b/autoloader.php

@@ -2,6 +2,17 @@
 
 require_once __DIR__ . '/vendor/autoload.php';
 
+// Registered *after* Composer's class loader: the third argument (prepend)
+// defaults to false, so this ends up at the back of the spl_autoload queue.
+//
+// \other12972\MyClass is part of Composer's class map (see composer.json), so at
+// runtime Composer's class loader resolves it first and this autoloader is never
+// invoked for it - running `php real-world.php` therefore never throws.
+//
+// PHPStan must mirror that order: the Composer class map source locator has to
+// resolve the class before this bootstrap autoloader is consulted. Analysing the
+// project used to invoke this autoloader first, hitting the LogicException and
+// crashing with an internal error that cannot happen at runtime.
 spl_autoload_register(function($class) {
 	if ($class === \other12972\MyClass::class) {
 		throw new LogicException('this should not happen');