fix: locking

mount_test.go

@@ -104,6 +104,16 @@ func TestLazyByIDShardFetchesMatchingPrefix(t *testing.T) {
 	if _, err := shard.(*lazyByIDShardNode).Lookup(context.Background(), "it-item-1.pdf"); err != nil {
 		t.Fatal(err)
 	}
+	lookupAgain, err := byID.(*lazyByIDNode).Lookup(context.Background(), "it")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if lookupAgain != shard {
+		t.Fatal("expected repeated shard lookup to return its cached node")
+	}
+	if _, err := lookupAgain.(*lazyByIDShardNode).Lookup(context.Background(), "it-item-1.pdf"); err != nil {
+		t.Fatal(err)
+	}
 	if len(queries) != 2 || queries[0] != "id:it*" || queries[1] != "id:it*" {
 		t.Fatalf("unexpected queries: %v", queries)
 	}