Add PromptKit catalog YAML encoders

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implement PromptKit comparison and catalogs
 
-Status: Stages 1–5 complete; remaining stages are planned.
+Status: Stages 1–6 complete; remaining stages are planned.
 
 ## Scope and authority
 
@@ -369,6 +369,19 @@ in Stage 8 once helpers are wired. Test decoded types, fields, sequence order,
 and empty inventories; incidental quoting style, private names, and indentation
 are not new contracts.
 
+**Completion evidence (2026-10-12)**
+
+- Added private YAML encoders that map native prompt identities to entries with
+  explicit string `id` and `version` fields and encode profile IDs as a bare
+  string sequence. Both return fully prepared bytes using the existing YAML
+  encoder; nil and allocated empty catalogs normalize to empty sequences.
+- Unit coverage decodes prompt entries and profile values to check field names,
+  string types, order, duplicates, whitespace, and numeric-looking values. Nil
+  and allocated empty inputs both encode as `[]`.
+- `GOTOOLCHAIN=local go test -count=1 .` passed in `integrations/ckprompt`.
+  Command-boundary schema coverage remains assigned to Stage 8; command wiring
+  and delivery remain assigned to Stage 7.
+
 ## Stage 7: Assemble and execute independent catalog commands
 
 **Outcome:** catalog commands and optional named-show commands share existing