09 Realtime Permissions - Spacetimedb

Canvas creator is the owner
Owner can set collaborator roles: viewer (can only watch) or editor (can draw)
Role changes take effect instantly - if you're demoted to viewer mid-stroke, it cancels
Owner can remove users from the canvas (they're kicked immediately)
Viewers see a "View Only" badge and all tools are disabled
Editors can't change permissions or remove others