Document PromptKit catalogs and smoke testing

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Dependency upgrades, discovery, and smoke testing implementation plan
 
-Status: Stages 1–16 complete; Stage 17 is next.
+Status: Stages 1–17 complete; Stage 18 is next.
 
 ## Authority and baseline
 
@@ -829,6 +829,16 @@ is required.
 **Complete when:** current contracts describe implemented behavior under their
 canonical owners and historical references remain correctly scoped.
 
+**Completed:** 2026-10-17. GoDoc, module summaries, the README, CLI reference,
+consumer guide, development commands, and internal inventory now describe the
+adopted source evidence, eight `FromEngine` callbacks, five catalogs, optional
+request validation, and native smoke behavior. Smoke examples and catalog
+commands were run against the maintained composed consumer; `go doc` confirmed
+the exported helper and request documentation. Local Markdown links/fragments,
+stale upstream revision references, and whitespace checks passed. Deferred-work
+scope and historical implementation-plan links were reconciled without changing
+historical API examples or release notes.
+
 ## Stage 18: Verify the complete target and finish
 
 1. Format all changed Go files and inspect the full diff for unrelated changes,