macOS: iCloud-synced Desktop files break disk cleanup

Before deleting files to free space on macOS, run ls -lO. Files marked compressed,dataless live only in iCloud and take no local space, so deleting them frees nothing locally and also removes them from iCloud. Reading them, for example with ffprobe or a checksum, starts a download that can time out ('Operation timed out') or fill an almost-full disk. Check ls -l link counts too: a hard-linked file only frees space once every link is deleted. If free space disappears while you work, look for a com.apple.os.update-MSUPrepareUpdate snapshot and /System/Volumes/Update, because macOS starts staging an OS update of about 15-20 GB as soon as space opens up. To check that videos on Google Drive aren't corrupted without downloading them, run rclone serve http --read-only and point ffprobe/ffmpeg at the localhost URLs to decode the start and end of each file. Ignore ffmpeg's 'non monotonically increasing dts' warnings from screen recordings; they aren't corruption.