Installer.php

<?php

namespace Foobar;

use Composer\Installers;
use Composer\Package\PackageInterface;
use Composer\Repository\InstalledRepositoryInterface;

class Installer extends \Composer\Installers\Installer {
  public function uninstall(InstalledRepositoryInterface $repo, PackageInterface $package) {
    echo "A1\n";
    if ('web/core' != substr($this->getInstallPath($package), -8)) {
      return parent::uninstall($repo, $package);
    }
    echo "B1\n";
    return NULL;
  }

  public function cleanup($type, PackageInterface $package, ?PackageInterface $prevPackage = null) {
    echo "A2\n";
    if ('web/core' != substr($this->getInstallPath($package), -8)) {
      return parent::cleanup($type, $package, $prevPackage);
    }
    echo "B2\n";
    return NULL;
  }
  
}