test: cover shared multi-directory package builds

lib/encoding/hex/hex_test.ww

@@ -9,7 +9,11 @@ package hex_test;
 
 import bytes;
 import errors;
-import hex;
+// Use the directory package's canonical identity. A recursive lib/... test
+// request also reaches this production package through crypto.sha256's
+// encoding.hex import, and one physical package must retain one identity in
+// the command-scoped package universe.
+import encoding.hex;
 import io;
 import memio;