Maintains the cluster membership list and the partition → primary/replica mapping.

Responsibilities

1. Membership tracking — reacts to :nodeup / :nodedown events forwarded by SuperCache.Cluster.NodeMonitor.
2. Partition map — builds and republishes a %{partition_idx => {primary, [replicas]}} map whenever membership changes. The map is stored in :persistent_term so hot-path reads are allocation-free (no GenServer hop).
3. Full sync — when a new node joins, triggers Replicator.push_partition/2 for every partition that this node owns (as primary or replica) so the joining node receives a consistent snapshot.

Cold-start behaviour

During application boot, SuperCache.Cluster.Bootstrap.start!/1 has not been called yet, so node_running?/1 returns false even for node() itself. The manager therefore always seeds the membership list with node() regardless of the health-check result, so the partition map is never built from an empty list. Remote peers are added only when the health-check confirms they are running.

Adding nodes at runtime

Nodes are added automatically via :nodeup events delivered by SuperCache.Cluster.NodeMonitor. You can also add a node manually:

SuperCache.Cluster.Manager.node_up(:peer@host)

Partition assignment

Partitions are assigned by rotating the sorted node list. With N nodes and replication factor R, partition idx gets:

• primary — sorted_nodes[idx mod N]
• replicas — the next min(R-1, N-1) nodes in the rotated list

This gives a balanced, deterministic assignment with no external coordination.