fix: stop writes to closed cluster sessions

server/cluster_order_test.go

@@ -4,6 +4,7 @@ import (
 	"net"
 	"net/rpc"
 	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -83,3 +84,31 @@ func TestClusterWriteLoopPreservesTopicOrder(t *testing.T) {
 		t.Fatalf("cluster responses arrived out of order: %v", proxy.received)
 	}
 }
+
+func TestClusterWriteLoopRejectsWritesAfterTermination(t *testing.T) {
+	previousSessionStore := globals.sessionStore
+	globals.sessionStore = NewSessionStore(time.Minute)
+	t.Cleanup(func() { globals.sessionStore = previousSessionStore })
+
+	sess := &Session{
+		sid:    "multiplex-termination-test",
+		proto:  MULTIPLEX,
+		send:   make(chan any, 1),
+		stop:   make(chan any, 1),
+		detach: make(chan string, 1),
+		subs:   make(map[string]*Subscription),
+	}
+	sess.stop <- nil
+
+	sess.clusterWriteLoop("grp-termination-test")
+
+	if atomic.LoadInt32(&sess.terminating) == 0 {
+		t.Fatal("terminated multiplexing session still accepts writes")
+	}
+	if !sess.queueOut(&ServerComMessage{TenantID: types.TenantID(1)}) {
+		t.Fatal("write to terminated multiplexing session should be discarded")
+	}
+	if len(sess.send) != 0 {
+		t.Fatalf("terminated multiplexing session retained %d outbound messages", len(sess.send))
+	}
+}