A Proxmox tag. Template VMs on the configured node carrying this exact tag are candidates; the comparison is case-insensitive (Proxmox stores tags lowercase by default, as a semicolon-separated list).
The tag is re-evaluated every time an agent is provisioned. When several templates match, the most recently
created wins: highest ctime from the VM config's meta property; templates without a
ctime (created before PVE 7.1, or restored from a backup) count as oldest; ties go to the highest
VM id. This suits templates that are rebuilt on a schedule under fresh VM ids: new agents pick up the newest
build automatically.
Provisioning fails when no template matches, so saving with zero current matches is allowed (the match count shown below this field is informational).