dashboard / erock/pico / chore(pubsub): add more tests #105 rss

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diff --git a/pkg/pubsub/regression_test.go b/pkg/pubsub/regression_test.go
new file mode 100644
index 0000000..c595c9b
--- /dev/null
+++ b/pkg/pubsub/regression_test.go
@@ -0,0 +1,408 @@
+package pubsub
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"log/slog"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// TestChannelMessageOrdering verifies that messages are delivered without panics or corruption.
+// This applies to both multicast and round-robin dispatchers.
+func TestChannelMessageOrdering(t *testing.T) {
+	name := "order-test"
+	numMessages := 3
+
+	// Test with Multicast
+	t.Run("Multicast", func(t *testing.T) {
+		cast := NewMulticast(slog.Default())
+		buf := new(Buffer)
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+		syncer := make(chan int)
+
+		// Subscribe
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			syncer <- 0
+			_ = cast.Sub(context.TODO(), "sub", buf, []*Channel{channel}, false)
+		}()
+
+		<-syncer
+
+		// Publish messages
+		for i := 0; i < numMessages; i++ {
+			wg.Add(1)
+			idx := i
+			go func() {
+				defer wg.Done()
+				msg := fmt.Sprintf("msg%d\n", idx)
+				_ = cast.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{channel}, false)
+			}()
+		}
+
+		wg.Wait()
+
+		// Verify at least some messages were received
+		content := buf.String()
+		if len(content) == 0 {
+			t.Error("Multicast: no messages received")
+		}
+	})
+
+	// Test with RoundRobin
+	t.Run("RoundRobin", func(t *testing.T) {
+		rr := NewRoundRobin(slog.Default())
+		buf := new(Buffer)
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+		syncer := make(chan int)
+
+		// Subscribe
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			syncer <- 0
+			_ = rr.Sub(context.TODO(), "sub", buf, []*Channel{channel}, false)
+		}()
+
+		<-syncer
+
+		// Publish messages
+		for i := 0; i < numMessages; i++ {
+			wg.Add(1)
+			idx := i
+			go func() {
+				defer wg.Done()
+				msg := fmt.Sprintf("msg%d\n", idx)
+				_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{channel}, false)
+			}()
+		}
+
+		wg.Wait()
+
+		// Verify at least some messages were received
+		content := buf.String()
+		if len(content) == 0 {
+			t.Error("RoundRobin: no messages received")
+		}
+	})
+}
+
+// TestDispatcherClientDirection verifies that both dispatchers respect client direction.
+// Publishers should not receive messages they publish.
+func TestDispatcherClientDirection(t *testing.T) {
+	name := "direction-test"
+
+	t.Run("Multicast", func(t *testing.T) {
+		cast := NewMulticast(slog.Default())
+		pubBuf := new(Buffer)
+		subBuf := new(Buffer)
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Publisher (input only)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = cast.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString("test")}, []*Channel{channel}, false)
+		}()
+
+		// Subscriber (output only)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = cast.Sub(context.TODO(), "sub", subBuf, []*Channel{channel}, false)
+		}()
+
+		wg.Wait()
+
+		// Publisher should not receive the message
+		if pubBuf.String() != "" {
+			t.Errorf("Publisher received message: %q", pubBuf.String())
+		}
+
+		// Subscriber should receive it
+		if subBuf.String() != "test" {
+			t.Errorf("Subscriber should have received message, got: %q", subBuf.String())
+		}
+	})
+
+	t.Run("RoundRobin", func(t *testing.T) {
+		rr := NewRoundRobin(slog.Default())
+		pubBuf := new(Buffer)
+		subBuf := new(Buffer)
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Publisher (input only)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString("test")}, []*Channel{channel}, false)
+		}()
+
+		// Subscriber (output only)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = rr.Sub(context.TODO(), "sub", subBuf, []*Channel{channel}, false)
+		}()
+
+		wg.Wait()
+
+		// Publisher should not receive the message
+		if pubBuf.String() != "" {
+			t.Errorf("Publisher received message: %q", pubBuf.String())
+		}
+
+		// Subscriber should receive it
+		if subBuf.String() != "test" {
+			t.Errorf("Subscriber should have received message, got: %q", subBuf.String())
+		}
+	})
+}
+
+// TestChannelConcurrentPublishes verifies that concurrent publishes don't cause races or data loss.
+func TestChannelConcurrentPublishes(t *testing.T) {
+	name := "concurrent-test"
+	numPublishers := 10
+	msgsPerPublisher := 5
+	numSubscribers := 3
+
+	t.Run("Multicast", func(t *testing.T) {
+		cast := NewMulticast(slog.Default())
+		buffers := make([]*Buffer, numSubscribers)
+		for i := range buffers {
+			buffers[i] = new(Buffer)
+		}
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Subscribe
+		for i := range buffers {
+			wg.Add(1)
+			idx := i
+			go func() {
+				defer wg.Done()
+				_ = cast.Sub(context.TODO(), fmt.Sprintf("sub-%d", idx), buffers[idx], []*Channel{channel}, false)
+			}()
+		}
+		time.Sleep(100 * time.Millisecond)
+
+		// Concurrent publishers
+		pubCount := int32(0)
+		for p := 0; p < numPublishers; p++ {
+			pubID := p
+			for m := 0; m < msgsPerPublisher; m++ {
+				wg.Add(1)
+				msgNum := m
+				go func() {
+					defer wg.Done()
+					msg := fmt.Sprintf("pub%d-msg%d\n", pubID, msgNum)
+					_ = cast.Pub(context.TODO(), fmt.Sprintf("pub-%d", pubID), &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{channel}, false)
+					atomic.AddInt32(&pubCount, 1)
+				}()
+			}
+		}
+
+		wg.Wait()
+
+		// Verify all messages delivered to all subscribers
+		totalExpectedMessages := numPublishers * msgsPerPublisher
+		for i, buf := range buffers {
+			messageCount := bytes.Count([]byte(buf.String()), []byte("\n"))
+			if messageCount != totalExpectedMessages {
+				t.Errorf("Subscriber %d: expected %d messages, got %d", i, totalExpectedMessages, messageCount)
+			}
+		}
+
+		// Verify all publishes completed
+		if pubCount != int32(totalExpectedMessages) {
+			t.Errorf("Expected %d publishes to complete, got %d", totalExpectedMessages, pubCount)
+		}
+	})
+
+	t.Run("RoundRobin", func(t *testing.T) {
+		rr := NewRoundRobin(slog.Default())
+		buffers := make([]*Buffer, numSubscribers)
+		for i := range buffers {
+			buffers[i] = new(Buffer)
+		}
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Subscribe
+		for i := range buffers {
+			wg.Add(1)
+			idx := i
+			go func() {
+				defer wg.Done()
+				_ = rr.Sub(context.TODO(), fmt.Sprintf("sub-%d", idx), buffers[idx], []*Channel{channel}, false)
+			}()
+		}
+		time.Sleep(100 * time.Millisecond)
+
+		// Concurrent publishers
+		pubCount := int32(0)
+		for p := 0; p < numPublishers; p++ {
+			pubID := p
+			for m := 0; m < msgsPerPublisher; m++ {
+				wg.Add(1)
+				msgNum := m
+				go func() {
+					defer wg.Done()
+					msg := fmt.Sprintf("pub%d-msg%d\n", pubID, msgNum)
+					_ = rr.Pub(context.TODO(), fmt.Sprintf("pub-%d", pubID), &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{channel}, false)
+					atomic.AddInt32(&pubCount, 1)
+				}()
+			}
+		}
+
+		wg.Wait()
+
+		// Verify all messages distributed (one to each subscriber per round-robin cycle)
+		// Allow for some timing variance - expect at least 90% of messages
+		totalExpectedMessages := numPublishers * msgsPerPublisher
+		totalDelivered := int32(0)
+		for _, buf := range buffers {
+			messageCount := bytes.Count([]byte(buf.String()), []byte("\n"))
+			totalDelivered += int32(messageCount)
+		}
+		minExpected := int32(float32(totalExpectedMessages) * 0.9)
+		if totalDelivered < minExpected {
+			t.Errorf("Expected at least %d messages, got %d", minExpected, totalDelivered)
+		}
+
+		// Verify all publishes completed
+		if pubCount != int32(totalExpectedMessages) {
+			t.Errorf("Expected %d publishes to complete, got %d", totalExpectedMessages, pubCount)
+		}
+	})
+}
+
+// TestDispatcherEmptySubscribers verifies that dispatchers handle empty subscriber set without panic.
+func TestDispatcherEmptySubscribers(t *testing.T) {
+	name := "empty-subs-test"
+
+	t.Run("Multicast", func(t *testing.T) {
+		cast := NewMulticast(slog.Default())
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Publish with no subscribers (should not panic)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			defer func() {
+				if r := recover(); r != nil {
+					t.Errorf("Multicast panicked with no subscribers: %v", r)
+				}
+			}()
+			_ = cast.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString("test")}, []*Channel{channel}, false)
+		}()
+
+		wg.Wait()
+		t.Log("Multicast handled empty subscribers correctly")
+	})
+
+	t.Run("RoundRobin", func(t *testing.T) {
+		rr := NewRoundRobin(slog.Default())
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Publish with no subscribers (should not panic)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			defer func() {
+				if r := recover(); r != nil {
+					t.Errorf("RoundRobin panicked with no subscribers: %v", r)
+				}
+			}()
+			_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString("test")}, []*Channel{channel}, false)
+		}()
+
+		wg.Wait()
+		t.Log("RoundRobin handled empty subscribers correctly")
+	})
+}
+
+// TestDispatcherSingleSubscriber verifies that both dispatchers work correctly with one subscriber.
+func TestDispatcherSingleSubscriber(t *testing.T) {
+	name := "single-sub-test"
+	message := "single-sub-message"
+
+	t.Run("Multicast", func(t *testing.T) {
+		cast := NewMulticast(slog.Default())
+		buf := new(Buffer)
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Subscribe
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = cast.Sub(context.TODO(), "sub", buf, []*Channel{channel}, false)
+		}()
+
+		time.Sleep(100 * time.Millisecond)
+
+		// Publish
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = cast.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(message)}, []*Channel{channel}, false)
+		}()
+
+		wg.Wait()
+
+		if buf.String() != message {
+			t.Errorf("Multicast with single subscriber: expected %q, got %q", message, buf.String())
+		}
+	})
+
+	t.Run("RoundRobin", func(t *testing.T) {
+		rr := NewRoundRobin(slog.Default())
+		buf := new(Buffer)
+		channel := NewChannel(name)
+
+		var wg sync.WaitGroup
+
+		// Subscribe
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = rr.Sub(context.TODO(), "sub", buf, []*Channel{channel}, false)
+		}()
+
+		time.Sleep(100 * time.Millisecond)
+
+		// Publish
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(message)}, []*Channel{channel}, false)
+		}()
+
+		wg.Wait()
+
+		if buf.String() != message {
+			t.Errorf("RoundRobin with single subscriber: expected %q, got %q", message, buf.String())
+		}
+	})
+}

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diff --git a/pkg/apps/pipe/cli.go b/pkg/apps/pipe/cli.go
index 32f1ec8..d8df279 100644
--- a/pkg/apps/pipe/cli.go
+++ b/pkg/apps/pipe/cli.go
@@ -600,6 +600,7 @@ func (handler *CliHandler) pub(cmd *CliCmd, topic string, clientID string) error
 	block := pubCmd.Bool("b", true, "Block writes until a subscriber is available")
 	timeout := pubCmd.Duration("t", 30*24*time.Hour, "Timeout as a Go duration to block for a subscriber to be available. Valid time units are 'ns', 'us' (or 'µs'), 'ms', 's', 'm', 'h'. Default is 30 days.")
 	clean := pubCmd.Bool("c", false, "Don't send status messages")
+	broker := pubCmd.String("bk", "multicast", "Type of broker (e.g. multicast, round_robin)")
 
 	if !flagCheck(pubCmd, topic, cmd.args) {
 		return fmt.Errorf("invalid cmd args")
@@ -619,6 +620,7 @@ func (handler *CliHandler) pub(cmd *CliCmd, topic string, clientID string) error
 		"topic", topic,
 		"access", *access,
 		"clean", *clean,
+		"broker", *broker,
 	)
 
 	var accessList []string
@@ -795,13 +797,20 @@ func (handler *CliHandler) pub(cmd *CliCmd, topic string, clientID string) error
 
 	throttledRW := newThrottledMonitorRW(rw, handler, cmd, name)
 
+	var bk psub.MessageDispatcher
+	bk = &psub.MulticastDispatcher{}
+	if *broker == "round_robin" {
+		fmt.Println("BROKER ROUND ROBIN")
+		bk = &psub.RoundRobinDispatcher{}
+	}
+	channel := psub.NewChannel(name)
+	channel.Dispatcher = bk
+
 	err := handler.PubSub.Pub(
 		cmd.pipeCtx,
 		clientID,
 		throttledRW,
-		[]*psub.Channel{
-			psub.NewChannel(name),
-		},
+		[]*psub.Channel{channel},
 		*block,
 	)
 

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diff --git a/pkg/pubsub/broker.go b/pkg/pubsub/broker.go
index e966c86..a523a81 100644
--- a/pkg/pubsub/broker.go
+++ b/pkg/pubsub/broker.go
@@ -196,6 +196,11 @@ func (b *BaseBroker) Connect(client *Client, channels []*Channel) (error, error)
 
 func (b *BaseBroker) ensureChannel(channel *Channel) *Channel {
 	dataChannel, _ := b.Channels.LoadOrStore(channel.Topic, channel)
+	// Allow overwriting the dispatcher
+	if channel.Dispatcher != nil && dataChannel.Dispatcher == nil {
+		dataChannel.Dispatcher = channel.Dispatcher
+	}
+
 	dataChannel.Handle()
 	return dataChannel
 }

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diff --git a/pkg/pubsub/channel.go b/pkg/pubsub/channel.go
index e8f4c3b..753b7eb 100644
--- a/pkg/pubsub/channel.go
+++ b/pkg/pubsub/channel.go
@@ -57,6 +57,7 @@ type Channel struct {
 	Clients     *syncmap.Map[string, *Client]
 	handleOnce  sync.Once
 	cleanupOnce sync.Once
+	Dispatcher  MessageDispatcher
 }
 
 func (c *Channel) GetClients() iter.Seq2[string, *Client] {
@@ -83,30 +84,21 @@ func (c *Channel) Handle() {
 				case <-c.Done:
 					return
 				case data, ok := <-c.Data:
-					var wg sync.WaitGroup
-					for _, client := range c.GetClients() {
-						if client.Direction == ChannelDirectionInput || (client.ID == data.ClientID && !client.Replay) {
-							continue
+					if !ok {
+						// Channel is closing, close all client data channels
+						for _, client := range c.GetClients() {
+							client.onceData.Do(func() {
+								close(client.Data)
+							})
 						}
-
-						wg.Add(1)
-						go func() {
-							defer wg.Done()
-							if !ok {
-								client.onceData.Do(func() {
-									close(client.Data)
-								})
-								return
-							}
-
-							select {
-							case client.Data <- data:
-							case <-client.Done:
-							case <-c.Done:
-							}
-						}()
+						return
 					}
-					wg.Wait()
+
+					// Collect eligible subscribers
+					subscribers := dispatcherForGetClients(c.GetClients(), data)
+
+					// Dispatch message using the configured dispatcher
+					_ = c.Dispatcher.Dispatch(data, subscribers, c.Done)
 				}
 			}
 		}()

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diff --git a/pkg/pubsub/dispatcher.go b/pkg/pubsub/dispatcher.go
new file mode 100644
index 0000000..df21854
--- /dev/null
+++ b/pkg/pubsub/dispatcher.go
@@ -0,0 +1,26 @@
+package pubsub
+
+import (
+	"iter"
+)
+
+// MessageDispatcher defines how messages are dispatched to subscribers.
+type MessageDispatcher interface {
+	// Dispatch sends a message to the appropriate subscriber(s).
+	// It receives the message, all subscribers, and the channel's sync primitives.
+	Dispatch(msg ChannelMessage, subscribers []*Client, channelDone chan struct{}) error
+}
+
+// dispatcherForGetClients collects eligible clients for dispatching.
+// Returns clients that should receive messages (output direction, not the sender unless replay).
+func dispatcherForGetClients(getClients iter.Seq2[string, *Client], msg ChannelMessage) []*Client {
+	subscribers := make([]*Client, 0)
+	for _, client := range getClients {
+		// Skip input-only clients and senders (unless replay is enabled)
+		if client.Direction == ChannelDirectionInput || (client.ID == msg.ClientID && !client.Replay) {
+			continue
+		}
+		subscribers = append(subscribers, client)
+	}
+	return subscribers
+}

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diff --git a/pkg/pubsub/multicast.go b/pkg/pubsub/multicast.go
index 23d5a71..180c20b 100644
--- a/pkg/pubsub/multicast.go
+++ b/pkg/pubsub/multicast.go
@@ -6,6 +6,7 @@ import (
 	"io"
 	"iter"
 	"log/slog"
+	"sync"
 
 	"github.com/antoniomika/syncmap"
 )
@@ -81,4 +82,24 @@ func (p *Multicast) Sub(ctx context.Context, ID string, rw io.ReadWriter, channe
 	return errors.Join(p.connect(ctx, ID, rw, channels, ChannelDirectionOutput, false, false, keepAlive))
 }
 
+// MulticastDispatcher sends each message to all eligible subscribers.
+type MulticastDispatcher struct{}
+
+func (d *MulticastDispatcher) Dispatch(msg ChannelMessage, subscribers []*Client, channelDone chan struct{}) error {
+	var wg sync.WaitGroup
+	for _, client := range subscribers {
+		wg.Add(1)
+		go func(cl *Client) {
+			defer wg.Done()
+			select {
+			case cl.Data <- msg:
+			case <-cl.Done:
+			case <-channelDone:
+			}
+		}(client)
+	}
+	wg.Wait()
+	return nil
+}
+
 var _ PubSub = (*Multicast)(nil)

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diff --git a/pkg/pubsub/roundrobin.go b/pkg/pubsub/roundrobin.go
new file mode 100644
index 0000000..e14db1f
--- /dev/null
+++ b/pkg/pubsub/roundrobin.go
@@ -0,0 +1,51 @@
+package pubsub
+
+import (
+	"slices"
+	"strings"
+	"sync"
+)
+
+/*
+RoundRobin is a load-balancing broker that distributes published messages
+to subscribers using a round-robin algorithm.
+
+Unlike Multicast which sends each message to all subscribers, RoundRobin
+sends each message to exactly one subscriber, rotating through the available
+subscribers for each published message. This provides load balancing for
+message processing.
+
+It maintains independent round-robin state per channel/topic.
+*/
+type RoundRobinDispatcher struct {
+	index uint32
+	mu    sync.Mutex
+}
+
+func (d *RoundRobinDispatcher) Dispatch(msg ChannelMessage, subscribers []*Client, channelDone chan struct{}) error {
+	// If no subscribers, nothing to dispatch
+	// BlockWrite behavior at publish time ensures subscribers are present when needed
+	if len(subscribers) == 0 {
+		return nil
+	}
+
+	slices.SortFunc(subscribers, func(a, b *Client) int {
+		return strings.Compare(a.ID, b.ID)
+	})
+
+	// Select the next subscriber in round-robin order
+	d.mu.Lock()
+	selectedIdx := int(d.index % uint32(len(subscribers)))
+	d.index++
+	d.mu.Unlock()
+
+	selectedClient := subscribers[selectedIdx]
+
+	select {
+	case selectedClient.Data <- msg:
+	case <-selectedClient.Done:
+	case <-channelDone:
+	}
+
+	return nil
+}

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diff --git a/pkg/pubsub/roundrobin_test.go b/pkg/pubsub/roundrobin_test.go
new file mode 100644
index 0000000..ca4618c
--- /dev/null
+++ b/pkg/pubsub/roundrobin_test.go
@@ -0,0 +1,354 @@
+package pubsub
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"log/slog"
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestRoundRobinSingleSub(t *testing.T) {
+	// Single publisher, single subscriber
+	// Should work like normal pub/sub
+	orderActual := ""
+	orderExpected := "sub-pub-"
+	actual := new(Buffer)
+	expected := "some test data"
+	name := "test-channel"
+	syncer := make(chan int)
+
+	rr := NewRoundRobin(slog.Default())
+
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	channel := NewChannel(name)
+
+	go func() {
+		orderActual += "sub-"
+		syncer <- 0
+		fmt.Println(rr.Sub(context.TODO(), "1", actual, []*Channel{channel}, false))
+		wg.Done()
+	}()
+
+	<-syncer
+
+	go func() {
+		orderActual += "pub-"
+		fmt.Println(rr.Pub(context.TODO(), "2", &Buffer{b: *bytes.NewBufferString(expected)}, []*Channel{channel}, true))
+		wg.Done()
+	}()
+
+	wg.Wait()
+
+	if orderActual != orderExpected {
+		t.Fatalf("\norderActual:(%s)\norderExpected:(%s)", orderActual, orderExpected)
+	}
+	if actual.String() != expected {
+		t.Fatalf("\nactual:(%s)\nexpected:(%s)", actual.String(), expected)
+	}
+}
+
+func TestRoundRobinMultipleSubs(t *testing.T) {
+	// Single publisher, multiple subscribers
+	// Verify round-robin distributes across subscribers
+	name := "test-channel"
+
+	rr := NewRoundRobin(slog.Default())
+
+	buffers := []*Buffer{new(Buffer), new(Buffer), new(Buffer)}
+	channel := NewChannel(name)
+
+	var wg sync.WaitGroup
+
+	// Subscribe three clients sequentially with sync point
+	syncer := make(chan int, 3)
+	for i := range buffers {
+		idx := i
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			clientID := fmt.Sprintf("sub-%d", idx)
+			_ = rr.Sub(context.TODO(), clientID, buffers[idx], []*Channel{channel}, false)
+		}()
+		syncer <- i
+	}
+
+	// Wait for all subscribers to connect
+	for i := 0; i < 3; i++ {
+		<-syncer
+	}
+	time.Sleep(200 * time.Millisecond)
+
+	// Publish many messages to verify distribution
+	numMsgs := 9
+	for i := 0; i < numMsgs; i++ {
+		wg.Add(1)
+		idx := i
+		go func() {
+			defer wg.Done()
+			msg := fmt.Sprintf("msg%d\n", idx)
+			_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{channel}, false)
+		}()
+	}
+
+	wg.Wait()
+
+	// Verify that messages were distributed across all subscribers
+	for i, buf := range buffers {
+		content := buf.String()
+		t.Logf("sub-%d received %d bytes", i, len(content))
+		if len(content) == 0 {
+			t.Logf("WARNING: sub-%d received no messages", i)
+		}
+	}
+
+	// At least one subscriber should have received messages
+	totalLen := 0
+	for _, buf := range buffers {
+		totalLen += len(buf.String())
+	}
+	if totalLen == 0 {
+		t.Fatal("No messages were delivered to any subscriber")
+	}
+}
+
+func TestRoundRobinDistribution(t *testing.T) {
+	// Verify that messages are distributed evenly across subscribers
+	expected := "msg"
+	name := "test-channel"
+	numSubs := 3
+	numMessages := 9
+
+	rr := NewRoundRobin(slog.Default())
+
+	buffers := make([]*Buffer, numSubs)
+	for i := 0; i < numSubs; i++ {
+		buffers[i] = new(Buffer)
+	}
+	channels := []*Channel{NewChannel(name)}
+
+	var wg sync.WaitGroup
+
+	// Subscribe clients
+	for i := 0; i < numSubs; i++ {
+		wg.Add(1)
+		idx := i
+		go func() {
+			defer wg.Done()
+			clientID := fmt.Sprintf("sub-%d", idx)
+			_ = rr.Sub(context.TODO(), clientID, buffers[idx], channels, false)
+		}()
+	}
+
+	time.Sleep(100 * time.Millisecond)
+
+	// Publish multiple messages
+	for i := 0; i < numMessages; i++ {
+		wg.Add(1)
+		msgIdx := i
+		go func() {
+			defer wg.Done()
+			msg := fmt.Sprintf("%s%d\n", expected, msgIdx)
+			_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(msg)}, channels, false)
+		}()
+	}
+
+	wg.Wait()
+
+	// Count messages per subscriber
+	msgCounts := make(map[int]int)
+	for i, buf := range buffers {
+		// Count occurrences of "msg" in the buffer
+		content := buf.String()
+		count := 0
+		for j := 0; j < numMessages; j++ {
+			marker := fmt.Sprintf("msg%d", j)
+			if bytes.Contains([]byte(content), []byte(marker)) {
+				count++
+			}
+		}
+		msgCounts[i] = count
+		t.Logf("sub-%d received %d messages", i, count)
+	}
+
+	// Verify relatively even distribution (within 1 message difference due to concurrency)
+	minCount := msgCounts[0]
+	maxCount := msgCounts[0]
+	for i := 1; i < numSubs; i++ {
+		if msgCounts[i] < minCount {
+			minCount = msgCounts[i]
+		}
+		if msgCounts[i] > maxCount {
+			maxCount = msgCounts[i]
+		}
+	}
+
+	if maxCount-minCount > 2 {
+		t.Fatalf("Uneven distribution: min=%d, max=%d, difference=%d", minCount, maxCount, maxCount-minCount)
+	}
+}
+
+func TestRoundRobinSubscriberJoinLeave(t *testing.T) {
+	// Test behavior when subscribers join and leave mid-stream
+	// Verify the broker gracefully handles subscriber changes
+	name := "test-channel"
+
+	rr := NewRoundRobin(slog.Default())
+	channel := NewChannel(name)
+
+	buf1 := new(Buffer)
+	buf2 := new(Buffer)
+	buf3 := new(Buffer)
+
+	var wg sync.WaitGroup
+
+	ctx1, cancel1 := context.WithCancel(context.Background())
+	ctx2, cancel2 := context.WithCancel(context.Background())
+
+	// Start with 2 subscribers
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		_ = rr.Sub(ctx1, "sub-1", buf1, []*Channel{channel}, false)
+	}()
+	go func() {
+		defer wg.Done()
+		_ = rr.Sub(ctx2, "sub-2", buf2, []*Channel{channel}, false)
+	}()
+
+	time.Sleep(200 * time.Millisecond)
+
+	// Publish some messages with 2 subscribers
+	for i := 0; i < 2; i++ {
+		wg.Add(1)
+		idx := i
+		go func() {
+			defer wg.Done()
+			msg := fmt.Sprintf("msg%d\n", idx)
+			_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{channel}, false)
+		}()
+	}
+	time.Sleep(100 * time.Millisecond)
+
+	// Remove sub-1
+	cancel1()
+	time.Sleep(200 * time.Millisecond)
+
+	// Add sub-3
+	ctx3, cancel3 := context.WithCancel(context.Background())
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		_ = rr.Sub(ctx3, "sub-3", buf3, []*Channel{channel}, false)
+	}()
+
+	time.Sleep(200 * time.Millisecond)
+
+	// Publish more messages with different subscriber set
+	for i := 2; i < 4; i++ {
+		wg.Add(1)
+		idx := i
+		go func() {
+			defer wg.Done()
+			msg := fmt.Sprintf("msg%d\n", idx)
+			_ = rr.Pub(context.TODO(), "pub", &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{channel}, false)
+		}()
+	}
+
+	wg.Wait()
+	cancel2()
+	cancel3()
+
+	t.Logf("sub-1: %d bytes", len(buf1.String()))
+	t.Logf("sub-2: %d bytes", len(buf2.String()))
+	t.Logf("sub-3: %d bytes", len(buf3.String()))
+
+	// Verify that messages were delivered (exact distribution depends on timing)
+	totalLen := len(buf1.String()) + len(buf2.String()) + len(buf3.String())
+	if totalLen == 0 {
+		t.Fatal("No messages were delivered after subscriber changes")
+	}
+}
+
+func TestRoundRobinMultipleChannels(t *testing.T) {
+	// Test that each channel maintains independent round-robin state
+	rr := NewRoundRobin(slog.Default())
+
+	ch1 := NewChannel("topic-1")
+	ch2 := NewChannel("topic-2")
+
+	buf1ch1 := new(Buffer)
+	buf2ch1 := new(Buffer)
+	buf1ch2 := new(Buffer)
+	buf2ch2 := new(Buffer)
+
+	var wg sync.WaitGroup
+
+	// Subscribe to channel 1
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		_ = rr.Sub(context.TODO(), "sub-1-ch1", buf1ch1, []*Channel{ch1}, false)
+	}()
+	go func() {
+		defer wg.Done()
+		_ = rr.Sub(context.TODO(), "sub-2-ch1", buf2ch1, []*Channel{ch1}, false)
+	}()
+
+	// Subscribe to channel 2
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		_ = rr.Sub(context.TODO(), "sub-1-ch2", buf1ch2, []*Channel{ch2}, false)
+	}()
+	go func() {
+		defer wg.Done()
+		_ = rr.Sub(context.TODO(), "sub-2-ch2", buf2ch2, []*Channel{ch2}, false)
+	}()
+
+	time.Sleep(100 * time.Millisecond)
+
+	// Publish to channel 1
+	wg.Add(2)
+	for i := 0; i < 2; i++ {
+		idx := i
+		go func() {
+			defer wg.Done()
+			msg := fmt.Sprintf("ch1-msg%d\n", idx)
+			_ = rr.Pub(context.TODO(), "pub-1", &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{ch1}, false)
+		}()
+	}
+
+	// Publish to channel 2
+	wg.Add(2)
+	for i := 0; i < 2; i++ {
+		idx := i
+		go func() {
+			defer wg.Done()
+			msg := fmt.Sprintf("ch2-msg%d\n", idx)
+			_ = rr.Pub(context.TODO(), "pub-2", &Buffer{b: *bytes.NewBufferString(msg)}, []*Channel{ch2}, false)
+		}()
+	}
+
+	wg.Wait()
+
+	t.Logf("ch1-buf1: %s", buf1ch1.String())
+	t.Logf("ch1-buf2: %s", buf2ch1.String())
+	t.Logf("ch2-buf1: %s", buf1ch2.String())
+	t.Logf("ch2-buf2: %s", buf2ch2.String())
+
+	// Both channels should have distributed messages independently
+	ch1Total := len(buf1ch1.String()) + len(buf2ch1.String())
+	ch2Total := len(buf1ch2.String()) + len(buf2ch2.String())
+
+	if ch1Total == 0 {
+		t.Fatal("Channel 1 should have received messages")
+	}
+	if ch2Total == 0 {
+		t.Fatal("Channel 2 should have received messages")
+	}
+}