Add PromptKit requirements validation command

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # PromptKit request validation implementation plan
 
-Status: Stages 1–3 complete; implementation is ongoing.
+Status: Stages 1–4 complete; implementation is ongoing.
 
 ## Authority, scope, and baseline
 
@@ -265,6 +265,16 @@ Run focused tests and the ckprompt suite.
 **Complete when:** the new command invokes the selected provider and produces
 the agreed YAML confirmation using existing core mechanics.
 
+**Completed:** 2026-10-12. Added `requirements validate` with typed selector
+preparation, presence-aware configuration selection, PromptKit request flags,
+repeatable variable and file bindings, and YAML confirmation output. `Command`
+now composes supplied show and validate declarations in one requirements group
+and retains issue reporting for absent capabilities. The assembled command test
+verifies callback values, first-`=` file paths, semantic YAML output, and both
+operations in help. Focused command tests and
+`GOTOOLCHAIN=local go test -count=1 ./...` passed from
+`integrations/ckprompt`.
+
 ## Stage 5: Cover command grammar, capability availability, and input lifetimes
 
 **Primary files:** a focused `integrations/ckprompt/validation_command_test.go`