Deploy GAE app with some composer packages outside vendor folder – SEO

I’m trying to install some packages outside the /vendor folder via the installer-paths composer directive.

After the deploy those packages aren’t installed in the deployment, but the ones in the vendor folders are.

There is any way to allow the Cloud build to install composer packages outside vendor folder?

I’m deploying a WordPress website to GAE php72, using a composer based boilerplate Bedrock.

I’ve tried to set the those paths to target custom folders inside the /vendor folder and it works, maybe there is some sort of security rules that allows composer install only to write into vendor?

Here is part of composer.json:

{
  // ...
  {
    "composer/installers": "^1.7",
    "wpackagist-plugin/wordpress-seo": ">=6.0",
    "wpackagist-theme/twentynineteen":"1.0"
  },
  "extra": {
    "installer-paths": {
      "web/app/mu-plugins/{$name}/": ["type:wordpress-muplugin"],
      "web/app/plugins/{$name}/": ["type:wordpress-plugin"],    
      "web/app/themes/{$name}/": ["type:wordpress-theme"]
    },
    "wordpress-install-dir": "web/wp"
  }
  //...
}

I’ve also tried to use composer post-install-cmd scripts to copy the packages from /vendor folder to the desired location, but the build fails with message:

Step #1 - "builder": Script cp vendor/plugins/* web/app/plugins handling the post-install-cmd event returned with error code 1
Step #1 - "builder": cp: target 'web/app/plugins' is not a directory
Step #1 - "builder": > cp vendor/plugins/* web/app/plugins