Initial aether repository structure

Distributed actor system with event sourcing for Go:
- event.go - Event, ActorSnapshot, EventStore interface
- eventbus.go - EventBus, EventBroadcaster for pub/sub
- nats_eventbus.go - NATS-backed cross-node event broadcasting
- store/ - InMemoryEventStore (testing), JetStreamEventStore (production)
- cluster/ - Node discovery, leader election, shard distribution
- model/ - EventStorming model types

Extracted from arcadia as open-source infrastructure component.

Co-Authored-By: Claude <noreply@anthropic.com>

cluster/types.go

@@ -0,0 +1,110 @@
+package cluster
+
+import (
+	"time"
+)
+
+const (
+	// NumShards defines the total number of shards in the cluster
+	NumShards = 1024
+	// VirtualNodes defines the number of virtual nodes per physical node for consistent hashing
+	VirtualNodes = 150
+	// Leadership election constants
+	LeaderLeaseTimeout = 10 * time.Second // How long a leader lease lasts
+	HeartbeatInterval  = 3 * time.Second  // How often leader sends heartbeats
+	ElectionTimeout    = 2 * time.Second  // How long to wait for election
+)
+
+// NodeStatus represents the health status of a node
+type NodeStatus string
+
+const (
+	NodeStatusActive   NodeStatus = "active"
+	NodeStatusDraining NodeStatus = "draining"
+	NodeStatusFailed   NodeStatus = "failed"
+)
+
+// NodeInfo represents information about a cluster node
+type NodeInfo struct {
+	ID        string            `json:"id"`
+	Address   string            `json:"address"`
+	Port      int               `json:"port"`
+	Status    NodeStatus        `json:"status"`
+	Capacity  float64           `json:"capacity"`  // Maximum load capacity
+	Load      float64           `json:"load"`      // Current CPU/memory load
+	LastSeen  time.Time         `json:"lastSeen"`  // Last heartbeat timestamp
+	Timestamp time.Time         `json:"timestamp"`
+	Metadata  map[string]string `json:"metadata"`
+	IsLeader  bool              `json:"isLeader"`
+	VMCount   int               `json:"vmCount"`   // Number of VMs on this node
+	ShardIDs  []int             `json:"shardIds"`  // Shards assigned to this node
+}
+
+// NodeUpdateType represents the type of node update
+type NodeUpdateType string
+
+const (
+	NodeJoined  NodeUpdateType = "joined"
+	NodeLeft    NodeUpdateType = "left"
+	NodeUpdated NodeUpdateType = "updated"
+)
+
+// NodeUpdate represents a node status update
+type NodeUpdate struct {
+	Type NodeUpdateType `json:"type"`
+	Node *NodeInfo      `json:"node"`
+}
+
+// ShardMap represents the distribution of shards across cluster nodes
+type ShardMap struct {
+	Version    uint64              `json:"version"`    // Incremented on each change
+	Shards     map[int][]string    `json:"shards"`     // shard ID -> [primary, replica1, replica2]
+	Nodes      map[string]NodeInfo `json:"nodes"`      // node ID -> node info
+	UpdateTime time.Time           `json:"updateTime"`
+}
+
+// ClusterMessage represents inter-node communication
+type ClusterMessage struct {
+	Type      string      `json:"type"`
+	From      string      `json:"from"`
+	To        string      `json:"to"`
+	Payload   interface{} `json:"payload"`
+	Timestamp time.Time   `json:"timestamp"`
+}
+
+// RebalanceRequest represents a request to rebalance shards
+type RebalanceRequest struct {
+	RequestID   string            `json:"requestId"`
+	FromNode    string            `json:"fromNode"`
+	ToNode      string            `json:"toNode"`
+	ShardIDs    []int             `json:"shardIds"`
+	Reason      string            `json:"reason"`
+	Migrations  []ActorMigration  `json:"migrations"`
+}
+
+// ActorMigration represents the migration of an actor between nodes
+type ActorMigration struct {
+	ActorID     string            `json:"actorId"`
+	FromNode    string            `json:"fromNode"`
+	ToNode      string            `json:"toNode"`
+	ShardID     int               `json:"shardId"`
+	State       map[string]interface{} `json:"state"`
+	Version     int64             `json:"version"`
+	Status      string            `json:"status"` // "pending", "in_progress", "completed", "failed"
+}
+
+// LeaderElectionCallbacks defines callbacks for leadership changes
+type LeaderElectionCallbacks struct {
+	OnBecameLeader func()
+	OnLostLeader   func()
+	OnNewLeader    func(leaderID string)
+}
+
+// LeadershipLease represents a leadership lease in the cluster
+type LeadershipLease struct {
+	LeaderID  string    `json:"leaderId"`
+	Term      uint64    `json:"term"`
+	ExpiresAt time.Time `json:"expiresAt"`
+	StartedAt time.Time `json:"startedAt"`
+}
+