Function get_watch_volume_data 

fn get_watch_volume_data(disks: &Disks, values: &mut HashMap<String, f64>)

Unix watch volume: the mount backing AgentMux’s data dir — where the store, logs and packaged builds land, so it is the volume whose filling up actually breaks this app.

Emits the same disk:watch:* summary and disk:vol:<mount>:watch / :is_system_drive markers the Windows path emits, so the status bar is platform-agnostic. Costs no syscall: it reads the Disks list already refreshed this tick, and reuses the free/total get_disk_data just computed rather than re-reading them.