Removes the HiveCopy hand-off: hive-c0re no longer writes each agent's
entry from swarm-agent-permissions.json into its runtime dir as
swarm-permissions.json, and the harness and subagent daemon no longer
read it. hive-c0re keeps the file as its own last read of the swarm for
the manage_root_agent mounts. Also removes permissions_import::pending(),
its only caller being the hand-off. No nix provisioned the copy, so no
nix option is removed and no tombstone is needed.
Rule after this change: until an agent's first successful read of its
key it holds no permissions (no execution, so no bash), and a subagent it
starts holds the same. After a read a set key wins, [] holds none and an
unset key is the default. A failed read keeps the last value, so an
unreachable queue at start keeps the agent closed until a read succeeds.
The harness logs once at warn that it starts closed.
Fixes#5315
2f00f9041f