🐛 Fix sync from zero

internal/store/sync_store_test.go

@@ -76,8 +76,8 @@ func TestSyncPruneStaleClient(t *testing.T) {
 		t.Fatalf("Prune: %v", err)
 	}
 
-	// A stale client (since=0) should get ErrSyncStale.
-	_, _, err := s.Pull(ctx, 0)
+	// A client with an existing sync position behind the marker is stale.
+	_, _, err := s.Pull(ctx, 1)
 	if !errors.Is(err, store.ErrSyncStale) {
 		t.Fatalf("expected ErrSyncStale, got %v", err)
 	}