Where to put temporary files when deploying?

Questions & Help Questions
,
1

I have a simple LiveView app that

  1. write user input to a temporary markup file (content.typ),
  2. drops to System.cmd/2 to process this markup with a CLI (typst), and
  3. deliver the output (content.png) to the client

In dev, I specify the path for the temporary files as

Application.app_dir(:typeset, "priv/static/uploads/")

and this works on my machine™.

I then have this dockerized and deployed on Fly, copying the Typst CLI to /bin and verified the CLI works by ssh in.

However, the temp files are now written to a directory that does not exist.

** (File.Error) could not write to file "/app/_build/prod/lib/typeset/priv/static/uploads/content.typ"

What is the proper way of handling temporary files, to be processed with a CLI, when deploying?