Make configuration values injectable rather than hardcoded

Add config structs with sensible defaults for tunable parameters:
- JetStreamConfig for stream retention (1 year) and replica count (1)
- HashRingConfig for virtual nodes per physical node (150)
- ShardConfig for shard count (1024) and replication factor (1)

Each component gets a new WithConfig constructor that accepts custom
configuration, while the original constructors continue to work with
defaults. Zero values in configs fall back to defaults for backward
compatibility.

Closes #38

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cluster/cluster.go

@@ -44,5 +44,4 @@
 // - Leader election ensures coordination continues despite node failures
 // - Actor migration allows rebalancing when cluster topology changes
 // - Graceful shutdown with proper resource cleanup
-//
+package cluster
-package cluster

cluster/config_test.go

@@ -0,0 +1,125 @@
+package cluster
+
+import (
+	"testing"
+)
+
+func TestDefaultHashRingConfig(t *testing.T) {
+	config := DefaultHashRingConfig()
+
+	if config.VirtualNodes != DefaultVirtualNodes {
+		t.Errorf("expected VirtualNodes=%d, got %d", DefaultVirtualNodes, config.VirtualNodes)
+	}
+}
+
+func TestDefaultShardConfig(t *testing.T) {
+	config := DefaultShardConfig()
+
+	if config.ShardCount != DefaultNumShards {
+		t.Errorf("expected ShardCount=%d, got %d", DefaultNumShards, config.ShardCount)
+	}
+	if config.ReplicationFactor != 1 {
+		t.Errorf("expected ReplicationFactor=1, got %d", config.ReplicationFactor)
+	}
+}
+
+func TestNewConsistentHashRingWithConfig(t *testing.T) {
+	t.Run("custom virtual nodes", func(t *testing.T) {
+		config := HashRingConfig{VirtualNodes: 50}
+		ring := NewConsistentHashRingWithConfig(config)
+
+		ring.AddNode("test-node")
+
+		if len(ring.sortedHashes) != 50 {
+			t.Errorf("expected 50 virtual nodes, got %d", len(ring.sortedHashes))
+		}
+		if ring.GetVirtualNodes() != 50 {
+			t.Errorf("expected GetVirtualNodes()=50, got %d", ring.GetVirtualNodes())
+		}
+	})
+
+	t.Run("zero value uses default", func(t *testing.T) {
+		config := HashRingConfig{VirtualNodes: 0}
+		ring := NewConsistentHashRingWithConfig(config)
+
+		ring.AddNode("test-node")
+
+		if len(ring.sortedHashes) != DefaultVirtualNodes {
+			t.Errorf("expected %d virtual nodes, got %d", DefaultVirtualNodes, len(ring.sortedHashes))
+		}
+	})
+
+	t.Run("default constructor uses default config", func(t *testing.T) {
+		ring := NewConsistentHashRing()
+
+		ring.AddNode("test-node")
+
+		if len(ring.sortedHashes) != DefaultVirtualNodes {
+			t.Errorf("expected %d virtual nodes, got %d", DefaultVirtualNodes, len(ring.sortedHashes))
+		}
+	})
+}
+
+func TestNewShardManagerWithConfig(t *testing.T) {
+	t.Run("custom shard count", func(t *testing.T) {
+		config := ShardConfig{ShardCount: 256, ReplicationFactor: 2}
+		sm := NewShardManagerWithConfig(config)
+
+		if sm.GetShardCount() != 256 {
+			t.Errorf("expected shard count 256, got %d", sm.GetShardCount())
+		}
+		if sm.GetReplicationFactor() != 2 {
+			t.Errorf("expected replication factor 2, got %d", sm.GetReplicationFactor())
+		}
+	})
+
+	t.Run("zero values use defaults", func(t *testing.T) {
+		config := ShardConfig{ShardCount: 0, ReplicationFactor: 0}
+		sm := NewShardManagerWithConfig(config)
+
+		if sm.GetShardCount() != DefaultNumShards {
+			t.Errorf("expected shard count %d, got %d", DefaultNumShards, sm.GetShardCount())
+		}
+		if sm.GetReplicationFactor() != 1 {
+			t.Errorf("expected replication factor 1, got %d", sm.GetReplicationFactor())
+		}
+	})
+
+	t.Run("legacy constructor still works", func(t *testing.T) {
+		sm := NewShardManager(512, 3)
+
+		if sm.GetShardCount() != 512 {
+			t.Errorf("expected shard count 512, got %d", sm.GetShardCount())
+		}
+		if sm.GetReplicationFactor() != 3 {
+			t.Errorf("expected replication factor 3, got %d", sm.GetReplicationFactor())
+		}
+	})
+}
+
+func TestShardManagerGetShard_DifferentShardCounts(t *testing.T) {
+	testCases := []struct {
+		shardCount int
+	}{
+		{shardCount: 16},
+		{shardCount: 64},
+		{shardCount: 256},
+		{shardCount: 1024},
+		{shardCount: 4096},
+	}
+
+	for _, tc := range testCases {
+		t.Run("shardCount="+string(rune(tc.shardCount)), func(t *testing.T) {
+			sm := NewShardManagerWithConfig(ShardConfig{ShardCount: tc.shardCount})
+
+			// Verify all actor IDs map to valid shard range
+			for i := 0; i < 1000; i++ {
+				actorID := "actor-" + string(rune(i))
+				shard := sm.GetShard(actorID)
+				if shard < 0 || shard >= tc.shardCount {
+					t.Errorf("shard %d out of range [0, %d)", shard, tc.shardCount)
+				}
+			}
+		})
+	}
+}

cluster/discovery.go

@@ -115,4 +115,4 @@ func (nd *NodeDiscovery) announceNode(updateType NodeUpdateType) {
 // Stop gracefully stops the node discovery service
 func (nd *NodeDiscovery) Stop() {
 	nd.announceNode(NodeLeft)
-}
+}

cluster/distributed.go

@@ -200,11 +200,11 @@ func (dvm *DistributedVM) GetClusterInfo() map[string]interface{} {
 	nodes := dvm.cluster.GetNodes()
 
 	return map[string]interface{}{
-		"nodeId":     dvm.nodeID,
+		"nodeId":    dvm.nodeID,
-		"isLeader":   dvm.cluster.IsLeader(),
+		"isLeader":  dvm.cluster.IsLeader(),
-		"leader":     dvm.cluster.GetLeader(),
+		"leader":    dvm.cluster.GetLeader(),
-		"nodeCount":  len(nodes),
+		"nodeCount": len(nodes),
-		"nodes":      nodes,
+		"nodes":     nodes,
 	}
 }
 
@@ -218,4 +218,4 @@ func (dvr *DistributedVMRegistry) GetActiveVMs() map[string]interface{} {
 // GetShard returns the shard number for the given actor ID
 func (dvr *DistributedVMRegistry) GetShard(actorID string) int {
 	return dvr.sharding.GetShard(actorID)
-}
+}

cluster/hashring.go

@@ -12,13 +12,24 @@ type ConsistentHashRing struct {
 	ring         map[uint32]string // hash -> node ID
 	sortedHashes []uint32          // sorted hash keys
 	nodes        map[string]bool   // active nodes
+	virtualNodes int               // number of virtual nodes per physical node
 }
 
-// NewConsistentHashRing creates a new consistent hash ring
+// NewConsistentHashRing creates a new consistent hash ring with default configuration
 func NewConsistentHashRing() *ConsistentHashRing {
+	return NewConsistentHashRingWithConfig(DefaultHashRingConfig())
+}
+
+// NewConsistentHashRingWithConfig creates a new consistent hash ring with custom configuration
+func NewConsistentHashRingWithConfig(config HashRingConfig) *ConsistentHashRing {
+	virtualNodes := config.VirtualNodes
+	if virtualNodes == 0 {
+		virtualNodes = DefaultVirtualNodes
+	}
 	return &ConsistentHashRing{
-		ring:  make(map[uint32]string),
+		ring:         make(map[uint32]string),
-		nodes: make(map[string]bool),
+		nodes:        make(map[string]bool),
+		virtualNodes: virtualNodes,
 	}
 }
 
@@ -31,7 +42,7 @@ func (chr *ConsistentHashRing) AddNode(nodeID string) {
 	chr.nodes[nodeID] = true
 
 	// Add virtual nodes for better distribution
-	for i := 0; i < VirtualNodes; i++ {
+	for i := 0; i < chr.virtualNodes; i++ {
 		virtualKey := fmt.Sprintf("%s:%d", nodeID, i)
 		hash := chr.hash(virtualKey)
 		chr.ring[hash] = nodeID
@@ -102,4 +113,9 @@ func (chr *ConsistentHashRing) GetNodes() []string {
 // IsEmpty returns true if the ring has no nodes
 func (chr *ConsistentHashRing) IsEmpty() bool {
 	return len(chr.nodes) == 0
-}
+}
+
+// GetVirtualNodes returns the number of virtual nodes per physical node
+func (chr *ConsistentHashRing) GetVirtualNodes() int {
+	return chr.virtualNodes
+}

cluster/hashring_test.go

@@ -42,7 +42,7 @@ func TestAddNode(t *testing.T) {
 	}
 
 	// Verify virtual nodes were added
-	expectedVirtualNodes := VirtualNodes
+	expectedVirtualNodes := DefaultVirtualNodes
 	if len(ring.sortedHashes) != expectedVirtualNodes {
 		t.Errorf("expected %d virtual nodes, got %d", expectedVirtualNodes, len(ring.sortedHashes))
 	}
@@ -86,7 +86,7 @@ func TestAddNode_MultipleNodes(t *testing.T) {
 		t.Errorf("expected 3 nodes, got %d", len(nodes))
 	}
 
-	expectedHashes := VirtualNodes * 3
+	expectedHashes := DefaultVirtualNodes * 3
 	if len(ring.sortedHashes) != expectedHashes {
 		t.Errorf("expected %d virtual nodes, got %d", expectedHashes, len(ring.sortedHashes))
 	}
@@ -118,7 +118,7 @@ func TestRemoveNode(t *testing.T) {
 	}
 
 	// Verify virtual nodes were removed
-	expectedHashes := VirtualNodes
+	expectedHashes := DefaultVirtualNodes
 	if len(ring.sortedHashes) != expectedHashes {
 		t.Errorf("expected %d virtual nodes, got %d", expectedHashes, len(ring.sortedHashes))
 	}
@@ -321,7 +321,7 @@ func TestRingBehavior_ManyNodes(t *testing.T) {
 	}
 
 	// Verify virtual nodes count
-	expectedHashes := numNodes * VirtualNodes
+	expectedHashes := numNodes * DefaultVirtualNodes
 	if len(ring.sortedHashes) != expectedHashes {
 		t.Errorf("expected %d virtual nodes, got %d", expectedHashes, len(ring.sortedHashes))
 	}
@@ -355,7 +355,7 @@ func TestRingBehavior_ManyNodes(t *testing.T) {
 	}
 }
 
-func TestVirtualNodes_ImproveDistribution(t *testing.T) {
+func TestDefaultVirtualNodes_ImproveDistribution(t *testing.T) {
 	// Test that virtual nodes actually improve distribution
 	// by comparing with a theoretical single-hash-per-node scenario
 
@@ -386,7 +386,7 @@ func TestVirtualNodes_ImproveDistribution(t *testing.T) {
 	stdDev := math.Sqrt(sumSquaredDiff / float64(numNodes))
 	coefficientOfVariation := stdDev / expectedPerNode
 
-	// With VirtualNodes=150, we expect good distribution
+	// With DefaultVirtualNodes=150, we expect good distribution
 	// Coefficient of variation should be low (< 15%)
 	if coefficientOfVariation > 0.15 {
 		t.Errorf("distribution has high coefficient of variation: %.2f%% (expected < 15%%)",
@@ -394,8 +394,8 @@ func TestVirtualNodes_ImproveDistribution(t *testing.T) {
 	}
 
 	// Verify that the actual number of virtual nodes matches expected
-	if len(ring.sortedHashes) != numNodes*VirtualNodes {
+	if len(ring.sortedHashes) != numNodes*DefaultVirtualNodes {
-		t.Errorf("expected %d virtual node hashes, got %d", numNodes*VirtualNodes, len(ring.sortedHashes))
+		t.Errorf("expected %d virtual node hashes, got %d", numNodes*DefaultVirtualNodes, len(ring.sortedHashes))
 	}
 }
 

cluster/leader.go

@@ -44,8 +44,8 @@ func NewLeaderElection(nodeID string, natsConn *nats.Conn, callbacks LeaderElect
 		Bucket:      "aether-leader-election",
 		Description: "Aether cluster leader election coordination",
 		TTL:         LeaderLeaseTimeout * 2, // Auto-cleanup expired leases
-		MaxBytes:    1024 * 1024,           // 1MB max
+		MaxBytes:    1024 * 1024,            // 1MB max
-		Replicas:    1,                     // Single replica for simplicity
+		Replicas:    1,                      // Single replica for simplicity
 	})
 	if err != nil {
 		// Try to get existing KV store
@@ -411,4 +411,4 @@ func (le *LeaderElection) updateCurrentLeader(leaderID string, term uint64) {
 			le.callbacks.OnNewLeader(leaderID)
 		}
 	}
-}
+}

cluster/manager.go

@@ -20,17 +20,17 @@ type VMRegistry interface {
 
 // ClusterManager coordinates distributed VM operations across the cluster
 type ClusterManager struct {
-	nodeID       string
+	nodeID      string
-	nodes        map[string]*NodeInfo
+	nodes       map[string]*NodeInfo
-	nodeUpdates  chan NodeUpdate
+	nodeUpdates chan NodeUpdate
-	shardMap     *ShardMap
+	shardMap    *ShardMap
-	hashRing     *ConsistentHashRing
+	hashRing    *ConsistentHashRing
-	election     *LeaderElection
+	election    *LeaderElection
-	natsConn     *nats.Conn
+	natsConn    *nats.Conn
-	ctx          context.Context
+	ctx         context.Context
-	mutex        sync.RWMutex
+	mutex       sync.RWMutex
-	logger       *log.Logger
+	logger      *log.Logger
-	vmRegistry   VMRegistry // Interface to access local VMs
+	vmRegistry  VMRegistry // Interface to access local VMs
 }
 
 // NewClusterManager creates a cluster coordination manager
@@ -328,4 +328,4 @@ func (cm *ClusterManager) GetShardMap() *ShardMap {
 		Nodes:      make(map[string]NodeInfo),
 		UpdateTime: cm.shardMap.UpdateTime,
 	}
-}
+}

cluster/shard.go

@@ -33,8 +33,26 @@ type ShardManager struct {
 	replication int
 }
 
-// NewShardManager creates a new shard manager
+// NewShardManager creates a new shard manager with default configuration
 func NewShardManager(shardCount, replication int) *ShardManager {
+	return NewShardManagerWithConfig(ShardConfig{
+		ShardCount:        shardCount,
+		ReplicationFactor: replication,
+	})
+}
+
+// NewShardManagerWithConfig creates a new shard manager with custom configuration
+func NewShardManagerWithConfig(config ShardConfig) *ShardManager {
+	// Apply defaults for zero values
+	shardCount := config.ShardCount
+	if shardCount == 0 {
+		shardCount = DefaultNumShards
+	}
+	replication := config.ReplicationFactor
+	if replication == 0 {
+		replication = 1
+	}
+
 	return &ShardManager{
 		shardCount:  shardCount,
 		shardMap:    &ShardMap{Shards: make(map[int][]string), Nodes: make(map[string]NodeInfo)},
@@ -149,6 +167,15 @@ func (sm *ShardManager) GetActorsInShard(shardID int, nodeID string, vmRegistry
 	return actors
 }
 
+// GetShardCount returns the total number of shards
+func (sm *ShardManager) GetShardCount() int {
+	return sm.shardCount
+}
+
+// GetReplicationFactor returns the replication factor
+func (sm *ShardManager) GetReplicationFactor() int {
+	return sm.replication
+}
 
 // ConsistentHashPlacement implements PlacementStrategy using consistent hashing
 type ConsistentHashPlacement struct{}
@@ -185,4 +212,4 @@ func (chp *ConsistentHashPlacement) RebalanceShards(currentMap *ShardMap, nodes
 	// This is a simplified implementation
 	// In practice, this would implement sophisticated rebalancing logic
 	return currentMap, nil
-}
+}

cluster/types.go

@@ -4,17 +4,47 @@ import (
 	"time"
 )
 
+// Default configuration values
 const (
-	// NumShards defines the total number of shards in the cluster
+	// DefaultNumShards defines the default total number of shards in the cluster
-	NumShards = 1024
+	DefaultNumShards = 1024
-	// VirtualNodes defines the number of virtual nodes per physical node for consistent hashing
+	// DefaultVirtualNodes defines the default number of virtual nodes per physical node
-	VirtualNodes = 150
+	DefaultVirtualNodes = 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
 )
 
+// HashRingConfig holds configuration for the consistent hash ring
+type HashRingConfig struct {
+	// VirtualNodes is the number of virtual nodes per physical node (default: 150)
+	VirtualNodes int
+}
+
+// DefaultHashRingConfig returns the default hash ring configuration
+func DefaultHashRingConfig() HashRingConfig {
+	return HashRingConfig{
+		VirtualNodes: DefaultVirtualNodes,
+	}
+}
+
+// ShardConfig holds configuration for shard management
+type ShardConfig struct {
+	// ShardCount is the total number of shards (default: 1024)
+	ShardCount int
+	// ReplicationFactor is the number of replicas per shard (default: 1)
+	ReplicationFactor int
+}
+
+// DefaultShardConfig returns the default shard configuration
+func DefaultShardConfig() ShardConfig {
+	return ShardConfig{
+		ShardCount:        DefaultNumShards,
+		ReplicationFactor: 1,
+	}
+}
+
 // NodeStatus represents the health status of a node
 type NodeStatus string
 
@@ -30,14 +60,14 @@ type NodeInfo struct {
 	Address   string            `json:"address"`
 	Port      int               `json:"port"`
 	Status    NodeStatus        `json:"status"`
-	Capacity  float64           `json:"capacity"`  // Maximum load capacity
+	Capacity  float64           `json:"capacity"` // Maximum load capacity
-	Load      float64           `json:"load"`      // Current CPU/memory load
+	Load      float64           `json:"load"`     // Current CPU/memory load
-	LastSeen  time.Time         `json:"lastSeen"`  // Last heartbeat timestamp
+	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
+	VMCount   int               `json:"vmCount"`  // Number of VMs on this node
-	ShardIDs  []int             `json:"shardIds"`  // Shards assigned to this node
+	ShardIDs  []int             `json:"shardIds"` // Shards assigned to this node
 }
 
 // NodeUpdateType represents the type of node update
@@ -57,9 +87,9 @@ type NodeUpdate struct {
 
 // ShardMap represents the distribution of shards across cluster nodes
 type ShardMap struct {
-	Version    uint64              `json:"version"`    // Incremented on each change
+	Version    uint64              `json:"version"` // Incremented on each change
-	Shards     map[int][]string    `json:"shards"`     // shard ID -> [primary, replica1, replica2]
+	Shards     map[int][]string    `json:"shards"`  // shard ID -> [primary, replica1, replica2]
-	Nodes      map[string]NodeInfo `json:"nodes"`      // node ID -> node info
+	Nodes      map[string]NodeInfo `json:"nodes"`   // node ID -> node info
 	UpdateTime time.Time           `json:"updateTime"`
 }
 
@@ -74,23 +104,23 @@ type ClusterMessage struct {
 
 // RebalanceRequest represents a request to rebalance shards
 type RebalanceRequest struct {
-	RequestID   string            `json:"requestId"`
+	RequestID  string           `json:"requestId"`
-	FromNode    string            `json:"fromNode"`
+	FromNode   string           `json:"fromNode"`
-	ToNode      string            `json:"toNode"`
+	ToNode     string           `json:"toNode"`
-	ShardIDs    []int             `json:"shardIds"`
+	ShardIDs   []int            `json:"shardIds"`
-	Reason      string            `json:"reason"`
+	Reason     string           `json:"reason"`
-	Migrations  []ActorMigration  `json:"migrations"`
+	Migrations []ActorMigration `json:"migrations"`
 }
 
 // ActorMigration represents the migration of an actor between nodes
 type ActorMigration struct {
-	ActorID     string            `json:"actorId"`
+	ActorID  string                 `json:"actorId"`
-	FromNode    string            `json:"fromNode"`
+	FromNode string                 `json:"fromNode"`
-	ToNode      string            `json:"toNode"`
+	ToNode   string                 `json:"toNode"`
-	ShardID     int               `json:"shardId"`
+	ShardID  int                    `json:"shardId"`
-	State       map[string]interface{} `json:"state"`
+	State    map[string]interface{} `json:"state"`
-	Version     int64             `json:"version"`
+	Version  int64                  `json:"version"`
-	Status      string            `json:"status"` // "pending", "in_progress", "completed", "failed"
+	Status   string                 `json:"status"` // "pending", "in_progress", "completed", "failed"
 }
 
 // LeaderElectionCallbacks defines callbacks for leadership changes
@@ -107,4 +137,3 @@ type LeadershipLease struct {
 	ExpiresAt time.Time `json:"expiresAt"`
 	StartedAt time.Time `json:"startedAt"`
 }
-

nats_eventbus.go

@@ -13,11 +13,11 @@ import (
 
 // NATSEventBus is an EventBus that broadcasts events across all cluster nodes using NATS
 type NATSEventBus struct {
-	*EventBus                             // Embed base EventBus for local subscriptions
+	*EventBus                       // Embed base EventBus for local subscriptions
-	nc                   *nats.Conn       // NATS connection
+	nc                   *nats.Conn // NATS connection
 	subscriptions        []*nats.Subscription
-	namespaceSubscribers map[string]int   // Track number of subscribers per namespace
+	namespaceSubscribers map[string]int // Track number of subscribers per namespace
-	nodeID               string           // Unique ID for this node
+	nodeID               string         // Unique ID for this node
 	mutex                sync.Mutex
 	ctx                  context.Context
 	cancel               context.CancelFunc

store/config_test.go

@@ -0,0 +1,46 @@
+package store
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDefaultJetStreamConfig(t *testing.T) {
+	config := DefaultJetStreamConfig()
+
+	if config.StreamRetention != DefaultStreamRetention {
+		t.Errorf("expected StreamRetention=%v, got %v", DefaultStreamRetention, config.StreamRetention)
+	}
+	if config.ReplicaCount != DefaultReplicaCount {
+		t.Errorf("expected ReplicaCount=%d, got %d", DefaultReplicaCount, config.ReplicaCount)
+	}
+}
+
+func TestJetStreamConfigDefaults(t *testing.T) {
+	t.Run("default stream retention is 1 year", func(t *testing.T) {
+		expected := 365 * 24 * time.Hour
+		if DefaultStreamRetention != expected {
+			t.Errorf("expected DefaultStreamRetention=%v, got %v", expected, DefaultStreamRetention)
+		}
+	})
+
+	t.Run("default replica count is 1", func(t *testing.T) {
+		if DefaultReplicaCount != 1 {
+			t.Errorf("expected DefaultReplicaCount=1, got %d", DefaultReplicaCount)
+		}
+	})
+}
+
+func TestJetStreamConfigCustomValues(t *testing.T) {
+	config := JetStreamConfig{
+		StreamRetention: 30 * 24 * time.Hour, // 30 days
+		ReplicaCount:    3,
+	}
+
+	if config.StreamRetention != 30*24*time.Hour {
+		t.Errorf("expected StreamRetention=30 days, got %v", config.StreamRetention)
+	}
+	if config.ReplicaCount != 3 {
+		t.Errorf("expected ReplicaCount=3, got %d", config.ReplicaCount)
+	}
+}

store/jetstream.go

@@ -11,29 +11,65 @@ import (
 	"github.com/nats-io/nats.go"
 )
 
+// Default configuration values for JetStream event store
+const (
+	DefaultStreamRetention = 365 * 24 * time.Hour // 1 year
+	DefaultReplicaCount    = 1
+)
+
+// JetStreamConfig holds configuration options for JetStreamEventStore
+type JetStreamConfig struct {
+	// StreamRetention is how long to keep events (default: 1 year)
+	StreamRetention time.Duration
+	// ReplicaCount is the number of replicas for high availability (default: 1)
+	ReplicaCount int
+}
+
+// DefaultJetStreamConfig returns the default configuration
+func DefaultJetStreamConfig() JetStreamConfig {
+	return JetStreamConfig{
+		StreamRetention: DefaultStreamRetention,
+		ReplicaCount:    DefaultReplicaCount,
+	}
+}
+
 // JetStreamEventStore implements EventStore using NATS JetStream for persistence
 type JetStreamEventStore struct {
 	js         nats.JetStreamContext
 	streamName string
-	mu         sync.Mutex                // Protects version checks during SaveEvent
+	config     JetStreamConfig
-	versions   map[string]int64          // actorID -> latest version cache
+	mu         sync.Mutex       // Protects version checks during SaveEvent
+	versions   map[string]int64 // actorID -> latest version cache
 }
 
-// NewJetStreamEventStore creates a new JetStream-based event store
+// NewJetStreamEventStore creates a new JetStream-based event store with default configuration
 func NewJetStreamEventStore(natsConn *nats.Conn, streamName string) (*JetStreamEventStore, error) {
+	return NewJetStreamEventStoreWithConfig(natsConn, streamName, DefaultJetStreamConfig())
+}
+
+// NewJetStreamEventStoreWithConfig creates a new JetStream-based event store with custom configuration
+func NewJetStreamEventStoreWithConfig(natsConn *nats.Conn, streamName string, config JetStreamConfig) (*JetStreamEventStore, error) {
 	js, err := natsConn.JetStream()
 	if err != nil {
 		return nil, fmt.Errorf("failed to get JetStream context: %w", err)
 	}
 
+	// Apply defaults for zero values
+	if config.StreamRetention == 0 {
+		config.StreamRetention = DefaultStreamRetention
+	}
+	if config.ReplicaCount == 0 {
+		config.ReplicaCount = DefaultReplicaCount
+	}
+
 	// Create or update the stream
 	stream := &nats.StreamConfig{
 		Name:      streamName,
 		Subjects:  []string{fmt.Sprintf("%s.events.>", streamName), fmt.Sprintf("%s.snapshots.>", streamName)},
 		Storage:   nats.FileStorage,
 		Retention: nats.LimitsPolicy,
-		MaxAge:    365 * 24 * time.Hour, // Keep events for 1 year
+		MaxAge:    config.StreamRetention,
-		Replicas:  1,                    // Can be increased for HA
+		Replicas:  config.ReplicaCount,
 	}
 
 	_, err = js.AddStream(stream)
@@ -44,6 +80,7 @@ func NewJetStreamEventStore(natsConn *nats.Conn, streamName string) (*JetStreamE
 	return &JetStreamEventStore{
 		js:         js,
 		streamName: streamName,
+		config:     config,
 		versions:   make(map[string]int64),
 	}, nil
 }