Verify captured configuration diff concurrency

docs/roadmap/implementation.md

@@ -159,6 +159,13 @@ sequence, sensitivity, and ordering cases.
 
 ## Stage 4: Verify Frozen State And Concurrent Inspection
 
+**Status: Complete.** The existing captured-source fixture now compares two
+views repeatedly after both sources become unreadable, and concurrently runs
+inspection, comparison, and offline execution against those captured engines.
+It confirms stable differences without source reads or comparison-triggered
+model calls. `GOTOOLCHAIN=local go test -race . ./internal/configuration
+./internal/engine` and `git diff --check` passed.
+
 Scope: lifecycle and concurrency integration tests.
 
 1. Reuse or extend the existing captured-source inspection fixture and counting