Verify configuration diff disclosure semantics

docs/roadmap/implementation.md

@@ -121,6 +121,12 @@ still behave as before. No runner or domain-package integration is needed.
 
 ## Stage 3: Verify Result Semantics And Sensitive Changes
 
+**Status: Complete.** Facade tests cover distinct source labels with equal
+effective values, absent versus null, atomic sequence changes, paired secret
+masking, sensitive shape replacement, and mutation of returned records.
+`GOTOOLCHAIN=local go test . ./internal/configuration` and
+`git diff --check` passed.
+
 Scope: focused facade integration tests, not a second comparator test suite.
 
 1. Extend the comparison tests with two valid engine configurations whose