diff --git a/test/e2e/sub2api_callback_flow_test.go b/test/e2e/sub2api_callback_flow_test.go
index 99345b0..d0b4576 100644
--- a/test/e2e/sub2api_callback_flow_test.go
+++ b/test/e2e/sub2api_callback_flow_test.go
@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
-	"sync"
 	"testing"
 	"time"
 
@@ -63,7 +62,7 @@ func resetE2EPlatformDB(t *testing.T, db *sql.DB) {
 	}
 }
 
-func newSub2APIE2EApp(t *testing.T, callbackURL string, callbackSecret string, maxRetries int) *app.App {
+func newSub2APIE2EApp(t *testing.T, db *sql.DB, callbackURL string, callbackSecret string, maxRetries int) *app.App {
 	t.Helper()
 	cfg := &config.Config{}
 	cfg.HTTP.Addr = ":0"
@@ -101,6 +100,9 @@ func newSub2APIE2EApp(t *testing.T, callbackURL string, callbackSecret string, m
 	}
 	t.Cleanup(func() {
 		_ = application.Shutdown(context.Background())
+		if db != nil {
+			_ = db.Close()
+		}
 	})
 	return application
 }
@@ -117,56 +119,52 @@ func eventually(t *testing.T, timeout time.Duration, fn func() bool) {
 	t.Fatal("condition not satisfied before timeout")
 }
 
-func waitForSessionEvents(t *testing.T, timeout time.Duration, mu *sync.Mutex, received *[]platformevent.Event, sessionID string, want int) []platformevent.Event {
+func waitForSessionEvents(t *testing.T, timeout time.Duration, eventsCh <-chan platformevent.Event, sessionID string, want int) []platformevent.Event {
 	t.Helper()
 	deadline := time.Now().Add(timeout)
+	var filtered []platformevent.Event
 	for time.Now().Before(deadline) {
-		mu.Lock()
-		filtered := make([]platformevent.Event, 0, len(*received))
-		for _, event := range *received {
+		select {
+		case event := <-eventsCh:
 			if event.SessionID == sessionID {
 				filtered = append(filtered, event)
 			}
+			if len(filtered) == want {
+				return filtered
+			}
+		case <-time.After(200 * time.Millisecond):
 		}
-		mu.Unlock()
-		if len(filtered) == want {
-			return filtered
-		}
-		time.Sleep(200 * time.Millisecond)
 	}
 
-	mu.Lock()
-	defer mu.Unlock()
-	snapshot := make([]string, 0, len(*received))
-	for _, event := range *received {
-		snapshot = append(snapshot, fmt.Sprintf("%s/%s", event.SessionID, event.EventType))
+	snapshot := make([]string, 0)
+	for {
+		select {
+		case event := <-eventsCh:
+			snapshot = append(snapshot, fmt.Sprintf("%s/%s", event.SessionID, event.EventType))
+		default:
+		}
+		break
 	}
-	t.Fatalf("session %s received %d events, want %d; snapshot=%v", sessionID, len(snapshot), want, snapshot)
+	t.Fatalf("session %s received %d events, want %d; snapshot=%v", sessionID, len(filtered), want, snapshot)
 	return nil
 }
 
 func TestSub2APICallbackFlow_ShouldDeliverOrderedEventsWithStableEventIDs(t *testing.T) {
 	db := openE2EPlatformDB(t)
-	defer db.Close()
 	resetE2EPlatformDB(t, db)
 
-	var (
-		mu       sync.Mutex
-		received []platformevent.Event
-	)
+	eventsCh := make(chan platformevent.Event)
 	callbackServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		mu.Lock()
-		defer mu.Unlock()
 		var event platformevent.Event
 		if err := json.NewDecoder(r.Body).Decode(&event); err != nil {
 			t.Fatalf("decode callback body failed: %v", err)
 		}
-		received = append(received, event)
+		eventsCh <- event
 		w.WriteHeader(http.StatusOK)
 	}))
 	defer callbackServer.Close()
 
-	application := newSub2APIE2EApp(t, callbackServer.URL, "sub2api-callback-secret", 3)
+	application := newSub2APIE2EApp(t, db, callbackServer.URL, "sub2api-callback-secret", 3)
 	server := httptest.NewServer(application.Server.Handler)
 	defer server.Close()
 
@@ -206,7 +204,7 @@ func TestSub2APICallbackFlow_ShouldDeliverOrderedEventsWithStableEventIDs(t *tes
 		t.Fatalf("ack session_id = %v, want non-empty", ack["session_id"])
 	}
 
-	filtered := waitForSessionEvents(t, 8*time.Second, &mu, &received, sessionID, 6)
+	filtered := waitForSessionEvents(t, 8*time.Second, eventsCh, sessionID, 6)
 	wantTypes := []string{
 		platformevent.TypeMessageReceived,
 		platformevent.TypeMessageProcessing,
@@ -247,7 +245,6 @@ func TestSub2APICallbackFlow_ShouldDeliverOrderedEventsWithStableEventIDs(t *tes
 
 func TestSub2APICallbackFlow_ShouldDeadLetterAfterMaxRetries(t *testing.T) {
 	db := openE2EPlatformDB(t)
-	defer db.Close()
 	resetE2EPlatformDB(t, db)
 
 	callbackServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
@@ -256,7 +253,7 @@ func TestSub2APICallbackFlow_ShouldDeadLetterAfterMaxRetries(t *testing.T) {
 	}))
 	defer callbackServer.Close()
 
-	application := newSub2APIE2EApp(t, callbackServer.URL, "sub2api-callback-secret", 1)
+	application := newSub2APIE2EApp(t, db, callbackServer.URL, "sub2api-callback-secret", 1)
 	server := httptest.NewServer(application.Server.Handler)
 	defer server.Close()