title: How to examine the contents of Heroku's build CACHE_DIR
body: <p>I have a production python app running in Heroku. I am able to update this app using git push. However, if I create a copy of this app, and clear the build cache by changing stack/python version to something else, then back, the app now generates errors that look like library dependency mismatches</p>
  <p>This means that my requirements.txt file seems to be incorrect, and the only way to build the app correctly is via whatever is in heroku's build cache. I'd like to download and examine the contents of the CACHE_DIR so I can fix my requirements.txt file so that it builds correctly from scratch</p>
  <p>I can find instructions on how to clear the build cache, but not how to download it and examine it.</p>