Per-instance registry of peer state — pubkey → {connection, last-seen address, status} — plus the auto-connect dispatcher.

Sits between PeerNet.Discovery (which emits "this pubkey is at this address") and PeerNet.Connection.Supervisor (which spins up sockets). When a discovery event arrives for a pubkey in the trust list, the Registry dials the address; the resulting Connection registers itself back here once authenticated.

State per peer

%{
  pubkey: <<...>>,
  status: :unknown | :discovered | :connecting | :connected | :disconnected,
  last_address: %{ip: ..., port: ...} | nil,
  last_seen: DateTime.t() | nil,
  conn_pid: pid() | nil
}

Public API

• lookup_connection/2 — returns {:ok, pid} or :not_connected (drop-in replacement for the previous PeerIndex behaviour the public PeerNet.send/4 and PeerNet.call/5 functions use).
• register_connection/3 — called by Connection when its handshake completes.
• list/1 — returns all known peers' state for UI / diagnostics.
• connected?/2 — convenience boolean.

Discovery integration

Receives {:peer_discovered, pubkey, address} and {:peer_lost, pubkey, _} messages from any PeerNet.Discovery implementation. Trust-checks the pubkey before acting.