Render only captured prompt templates

docs/internal/runner.md

@@ -42,6 +42,8 @@ Ordinary preparation selects the full prompt definition and construction-time
 hash. It retains its early request-ID check before direct-session
 normalization. Referenced message content and static template syntax were
 captured when the engine was built.
+Rendering uses those captured parses, cloning them per call to bind request
+input helpers; it does not parse templates during execution.
 
 `InspectPrompt` selects captured metadata directly from the repository. It
 returns owned metadata without

docs/roadmap/implementation.md

@@ -165,6 +165,10 @@ inspection tests. Renderer-related failures may be deferred through Stage 6.
 
 ## Stage 5: Keep Only Captured Rendering
 
+**Completed:** Rendering now requires captured templates and no longer parses
+messages or sessions per call. Go 1.27.3 `go build ./...` passed; renderer and
+use-case test migrations and their checks are deferred to the next stage.
+
 **Finding:** 3. **Files:** `internal/prompt/go_renderer.go`, template helpers, engine assembly.
 
 1. Remove `NewGoRenderer` and the nil-template lookup mode. Keep