How an upload lands

devmachine upload exists so an app or an agent can hand a file to a workspace and get back a path it can use. Each rule below serves that.

It runs as the account the file is for

With --workspace, the CLI logs in as the workspace’s own account, the same way run --workspace does. Every folder and file it makes is that account’s from the start. Root never writes into a workspace’s home, so there is nothing to hand over with a chown, and nothing root could be tricked into writing somewhere else.

A new name every time, never an overwrite

The time goes before the extension (report-20260930-143012.pdf), so a second upload of the same file does not replace the first, and the file still opens with the right program. When two uploads land in the same second, the second gets -2.

The file arrives under a temporary name and is then linked to its final name. A link fails when the name is taken, instead of replacing what is there, so even two uploads at the same moment cannot overwrite each other. A half-sent file never shows up under its final name.

It stays inside the home

--dir is checked twice. On your computer, a folder that climbs out with ../ is refused before anything connects. On the machine, the nearest existing folder on the way is resolved, and if it leads out of the home through a symbolic link, the upload stops before it writes. A link that stays inside the home is fine.

A folder named with accents is matched the same way download matches one: when --dir as given is not on the machine, its composed form is used, so a Mac app that sends it decomposed does not get a twin folder next to the real one. See how a download lands.

A file name is never a command

The name of a file is whatever its owner typed, and a name like '; rm -rf ~; $(id).txt is legal. The CLI sends names to the machine encoded in base64, and the machine decodes them into variables. The name is never part of a command line, so nothing in it can run.

The file’s content travels on standard input, over the same SSH connection run keeps open, so many uploads in a row share one login.