composer-install of Drupal8 creates a tmp####/ folder. How to manage & clean it? I'm working with Drupal, with v8, using Composer to install &amp; manage it.

I create a new Drupal8 project using the 'drupal-composer/drupal-project' template,

composer create-project --keep-vcs --stability dev --no-interaction drupal-composer/drupal-project:8.x-dev mysite


That installs

tree mysite  -L 1
    mysite
    ├── composer.json
    ├── composer.lock
    ├── drush
    ├── LICENSE
    ├── phpunit.xml.dist
    ├── README.md
    ├── scripts
    ├── tmp12972441691459034756
    ├── vendor
    └── web


If you look inside that 'tmp#' folder

tree mysite/tmp12972441691459034756 -L 2
    mysite/tmp12972441691459034756
    └── drupal-8.0.5
        ├── autoload.php
        ├── composer.json
        ├── composer.lock
        ├── core
        ├── example.gitignore
        ├── index.php
        ├── LICENSE.txt
        ├── modules
        ├── profiles
        ├── README.txt
        ├── robots.txt
        ├── sites
        ├── themes
        ├── update.php
        ├── vendor
        └── web.config


it looks like a complete copy of the source.

Afaict, it's used only on the first install, and doesn't ever seem to get cleaned up or deleted (by cron etc).

Do I need to keep those files around for some reason?  Or is it safe to just delete that folder?

Is there a Drupal8 maintenance task, maybe cron, that should be cleaning it out?

I've read older comments on this, and there's references to old versions' "/tmp" usage, but this is not that I guess, and this has a hash.  Anyway, I don't see the Drupal8-specific usage instructions anywhere.
You shouldn't keep the tmp folder. The scaffolding plugin should delete tmp folder after it copied the necessary files into the web folder. Not sure what went wrong on your machine.

Fixed in https://github.com/drupal-composer/drupal-scaffold/issues/33