fix: skip sync.Once in snapshotStruct to prevent false-positive divergence (#87)

Author: qj0r9j0vc2

tracker/tracker.go

@@ -128,11 +128,12 @@ func snapshotVal(v reflect.Value, buf *bytes.Buffer, visited map[uintptr]bool, d
 var (
 	mutexType   = reflect.TypeOf(sync.Mutex{})
 	rwMutexType = reflect.TypeOf(sync.RWMutex{})
+	onceType    = reflect.TypeOf(sync.Once{})
 )
 
 func snapshotStruct(v reflect.Value, buf *bytes.Buffer, visited map[uintptr]bool, depth int, trk *KeeperReflectTracker) {
 	typ := v.Type()
-	if typ == mutexType || typ == rwMutexType {
+	if typ == mutexType || typ == rwMutexType || typ == onceType {
 		return
 	}
 

tracker/tracker_test.go

@@ -179,6 +179,19 @@ func TestSnapshot_DeepNesting_NoPanic(t *testing.T) {
 
 // ── Filtering: mutex and function fields ─────────────────────────────────────
 
+func TestSnapshot_OnceNotTracked(t *testing.T) {
+	type S struct {
+		once sync.Once
+		N    int
+	}
+	s := &S{N: 5}
+	tr := New(s)
+	snap1 := tr.SnapshotOutOfKVStoreState()
+	s.once.Do(func() {}) // transitions done: 0 → 1
+	snap2 := tr.SnapshotOutOfKVStoreState()
+	require.Equal(t, snap1, snap2, "sync.Once state must not affect snapshot")
+}
+
 func TestSnapshot_MutexNotTracked(t *testing.T) {
 	type S struct {
 		mu sync.Mutex