- clone each file with FICLONE, copy the data only where that fails
- skip the salvage when the copy would leave too little free space
- hold a per-container flock and one copy at a time across containers
- run WriteNspawnFlags on the blocking pool
hive-priv copies a stopped container's root to the agent's work dir and
renames it aside before passing nspawn --ephemeral; the agent's nix state
moves to the persistent profiles bind. Adds the agent-ephemeral-rootfs vm
test and a module-eval case for the nix state redirect.
