It turns out the library hiccups when using a RAM buffer. I now save the files to /tmp, and create a ReadStream, and now it works! The rest of the time was spent writing a Nix flake, which both wraps the package (currently using a shell script, until I figure out how to run deno compile in the offline sandbox), and contains a NixOS module, which creates a systemd timer to run the bot as a oneshot service.