feat: storage sync/async funcs

pkg/storage/fs/fs_test.go

@@ -22,6 +22,39 @@ type callbackResult[T any] struct {
 	err   error
 }
 
+func TestStateRoundTrip(t *testing.T) {
+	s := newTestStorage(t)
+	want := sampleState()
+
+	exists, err := s.StateExists()
+	if err != nil {
+		t.Fatalf("state exists before save: %v", err)
+	}
+	if exists {
+		t.Fatal("state file should not exist before save")
+	}
+
+	if err := s.SaveState(want); err != nil {
+		t.Fatalf("save state: %v", err)
+	}
+
+	exists, err = s.StateExists()
+	if err != nil {
+		t.Fatalf("state exists after save: %v", err)
+	}
+	if !exists {
+		t.Fatal("state file should exist after save")
+	}
+
+	got, err := s.LoadState()
+	if err != nil {
+		t.Fatalf("load state: %v", err)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("loaded state mismatch\nwant: %#v\ngot:  %#v", want, got)
+	}
+}
+
 func TestStateRoundTripAsync(t *testing.T) {
 	s := newTestStorage(t)
 	want := sampleState()