The files API reads and writes the sandbox filesystem as the sandbox user. Paths are absolute, or relative to /home/user.

Watch a directory

watch.py

Signed upload and download URLs

Hand a URL to a browser or another service so it can move a file without your API key. The URL is signed for one path and expires.
signed_urls.py

Copy files with the CLI

Over SSH (see SSH):
scp.sh
Coming soon: anona-compute push, which copies a git working tree into a sandbox.