Reserve Promptkit catalog profile names

docs/internal/sources.md

@@ -72,6 +72,10 @@ manifest, layout, profile ownership, inheritance, and secret-safety rules
 before returning raw catalog sources. Internal engine assembly uses those validated
 catalogs as the maintained lowest-precedence profile source.
 
+Normalized external catalog profile IDs with the exact `promptkit-` prefix are
+rejected at this adapter boundary. That reservation applies only to imported
+catalogs; configured consumer sources retain the ordinary profile-ID rules.
+
 The overlay repository consults the next repository only when the
 higher-precedence repository reports that a profile is absent. A reliably
 selected malformed profile stops fallback, while an unrelated malformed file

docs/roadmap/implementation.md

@@ -128,6 +128,8 @@ checkouts, workspaces, or replacements.
 
 ## Stage 3: Enforce The External Catalog Namespace
 
+**Completed:** 2026-09-22
+
 Repository: Promptkit. Keep current v1 dependencies during this stage;
 dependency adoption remains atomic in Stage 5.