jademind/slack-files-download ? reverse-engineered prompt

Build me a small Python command line tool that scans a Slack workspace export folder and downloads all attached files from the message JSON files.

It should go through each channel, make a separate folder for it inside an output directory, and save the linked files there. If a file was already downloaded, it should skip it so I can run it again later for incremental backups. I want it to be easy to use from the terminal with a path to the Slack export folder, and an optional way to choose the output folder, plus a help message.

Please keep it simple and reliable, since the main use is backing up my Slack files before closing an account. If you need to check current Python docs or best practices for CLI argument parsing and file downloading, go ahead and look them up.