GlobalPid
GlobalPid: a serializable, cluster-wide process handle (P1 L4 prerequisite).
Location-transparent send/cast/call need a process identity that survives the wire. A global Pid is {NodeId, local_pid, creation}: the owning node, the node-local scheduler pid (the runtime's integer PID), and a creation counter that distinguishes a restarted node's reused local pids from the originals (so a stale Pid from before a restart is detectably stale). It round-trips through MessagePack to ride inside a NetFrame.