Complete procedures with a way back.

Add a reviewed global IPv6 address alongside existing IPv4, learn the default route through authenticated network ownership rather than assumption, preserve Neighbor Discovery and Path MTU Discovery, and apply one consistent nftables policy to both families with timed recovery.

Build a redundant active-backup bond, carry a tagged service VLAN over it, terminate the host address on a Linux bridge, and introduce the topology through `netplan try` with automatic rollback, console recovery, and explicit switch-side evidence.