[php-src] Issue #20999: How to intercept in advance?

Issue: https://github.com/php/php-src/issues/20999
Author: wheakerd

### Description

The following code:

```php
<?php
declare(strict_types=1);

final class ReflectorCollector
{
	private static array $reflections = [
		'class'             => [],
		'class_constant'    => [],
		'constant'          => [],
		'enum'              => [],
		'enum_units'        => [],
		'enum_backed_cases' => [],
	];

	public static function reflectEnum(string $class): ReflectionEnum
	{
		if (!isset(self::$reflections['enum'][$class])) {
			if (!enum_exists($class)) {
				throw new ReflectorException("The enum \"$class\" does not exist.");
			}
			self::$reflections['enum'][$class] = new ReflectionEnum($class);
		}
		return self::$reflections['enum'][$class];
	}

	public static function reflectEnumUnitCase(string $class, string $constant): ReflectionEnumUnitCase
	{
		if (!isset(self::$reflections['enum_units']["$class::$constant"])) {
			$reflectionEnum = self::reflectEnum($class);
			if (!$reflectionEnum->hasCase($constant)) {
				throw new ReflectorException("The case \"$constant\" does not exist in enum \"$class\".");
			}
            // see here
			self::$reflections['enum_units']["$class::$constant"] = $reflectionEnum->getCase($constant);
		}
		return self::$reflections['enum_units']["$class::$constant"];
	}
}
```

Resulted in this output:
```
Why might `self::$reflections['enum_units']["$class::$constant"] = $reflectionEnum->getCase($constant);` throw an exception?
```

But I expected this output instead:
```
No exception was thrown.
```


### PHP Version

```plain
PHP 8.4.14 (cli) (built: Oct 25 2025 03:34:16) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.14, Copyright (c) Zend Technologies
```

### Operating System

24.04.3 LTS (Noble Numbat)