Verify PromptKit comparison through config commands

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implement PromptKit comparison and catalogs
 
-Status: Stages 1–3 complete; remaining stages are planned.
+Status: Stages 1–4 complete; remaining stages are planned.
 
 ## Scope and authority
 
@@ -268,6 +268,26 @@ expectation is knowingly pending Stage 9; do not report the whole suite as passi
 while it remains. Keep assertions on semantic reports and supported outcomes,
 not exact diagnostic snapshots or private layout.
 
+**Completion evidence (2026-10-12)**
+
+- Added external-package integration coverage that installs `ckconfig.Command`
+  with the real `ckprompt.ConfigScope`, an app scope, and a public
+  `commandkit.App`. It compares two native PromptKit engines and decodes the
+  existing additions/changes/deletions YAML report, including a meaningful
+  change.
+- Verified explicit left/right selection, omitted-right inheritance, and a
+  supplied empty right override. The same captured campaign selector reaches
+  separately prepared left/right inputs; both checks finish before shared state
+  creation, and the provider receives those inputs and state.
+- Confirmed bare diff uses the app scope, scope `all` is rejected before engine
+  loading, installed ConfigKit failure preserves its `LoadError` identity and
+  left-side diagnostic heading, and help/version/scope discovery do not load an
+  engine. Narrowed discovery lists only enabled operations, and Show remains
+  usable after Diff is cleared.
+- `GOTOOLCHAIN=local go test -count=1 .` passed in `integrations/ckprompt`.
+  The composed example's obsolete negative expectation remains assigned to
+  Stage 9; no full-module pass is claimed here.
+
 ## Stage 5: Add optional catalog providers to the public suite
 
 **Outcome:** either catalog can be supplied independently, and `FromEngine`