OK, snapshot 0 can be used in snapper commands and it indeed refers to the current active root:
bor@uefi:~> sudo snapper diff 777..0
--- /.snapshots/777/snapshot/etc/cups/subscriptions.conf 2025-12-09 20:53:12.908924143 +0300
+++ /etc/cups/subscriptions.conf 2025-12-11 20:54:13.229494997 +0300
@@ -1,21 +1,21 @@
# Subscription configuration file for CUPS v2.4.14
# Written by cupsd
...
I am not going to perform rollback to test what happens when the current root is not the snapshot 1 ![]()