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

internal/prompt/go_renderer.go

@@ -24,10 +24,6 @@ type goRenderer struct {
 	templates TemplateLookup
 }
 
-func NewGoRenderer() Renderer {
-	return &goRenderer{}
-}
-
 // NewCompiledRenderer renders definitions using templates captured with the
 // configuration snapshot. Per-call clones bind request-specific input helpers.
 func NewCompiledRenderer(templates TemplateLookup) Renderer {
@@ -56,13 +52,12 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 	funcs := template.FuncMap{
 		"input": resolver.resolve,
 	}
-	var compiled CompiledTemplates
+	if r.templates == nil {
-	if r.templates != nil {
+		return nil, fmt.Errorf("%w: captured templates are unavailable", ErrRenderFailure)
-		var found bool
+	}
-		compiled, found = r.templates.GetCompiledTemplates(definition.ID)
+	compiled, found := r.templates.GetCompiledTemplates(definition.ID)
-		if !found || len(compiled.Messages) != len(definition.Templates) {
+	if !found || len(compiled.Messages) != len(definition.Templates) {
-			return nil, fmt.Errorf("%w: captured templates are unavailable", ErrRenderFailure)
+		return nil, fmt.Errorf("%w: captured templates are unavailable", ErrRenderFailure)
-		}
 	}
 
 	if err := ctx.Err(); err != nil {
@@ -70,15 +65,11 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 	}
 	var sessionID string
 	var err error
-	if r.templates != nil {
+	if definition.SessionID != "" {
-		if definition.SessionID != "" {
+		if compiled.Session == nil {
-			if compiled.Session == nil {
+			return nil, fmt.Errorf("%w: captured session template is unavailable", ErrRenderFailure)
-				return nil, fmt.Errorf("%w: captured session template is unavailable", ErrRenderFailure)
-			}
-			sessionID, err = renderCompiledSessionID(ctx, compiled.Session, funcs, vars)
 		}
-	} else {
+		sessionID, err = renderCompiledSessionID(ctx, compiled.Session, funcs, vars)
-		sessionID, err = renderSessionID(ctx, definition.SessionID, funcs, vars)
 	}
 	if err != nil {
 		return nil, err
@@ -102,18 +93,12 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 		if err := ctx.Err(); err != nil {
 			return nil, err
 		}
-		var tmpl *template.Template
+		if compiled.Messages[i] == nil {
-		var parseErr error
+			return nil, fmt.Errorf("%w: captured message template is unavailable", ErrRenderFailure)
-		if r.templates != nil {
+		}
-			if compiled.Messages[i] == nil {
+		tmpl, parseErr := compiled.Messages[i].Clone()
-				return nil, fmt.Errorf("%w: captured message template is unavailable", ErrRenderFailure)
+		if parseErr == nil {
-			}
+			tmpl.Funcs(funcs)
-			tmpl, parseErr = compiled.Messages[i].Clone()
-			if parseErr == nil {
-				tmpl.Funcs(funcs)
-			}
-		} else {
-			tmpl, parseErr = parseTemplate(fmt.Sprintf("msg_%d", i), tmplMsg.Content, funcs)
 		}
 		if err := ctx.Err(); err != nil {
 			return nil, err
@@ -201,20 +186,6 @@ func (r *artifactTextResolver) resolve(name string) (string, error) {
 	return text, nil
 }
 
-func renderSessionID(ctx context.Context, raw string, funcs template.FuncMap, vars map[string]string) (string, error) {
-	if err := ctx.Err(); err != nil {
-		return "", err
-	}
-	tmpl, parseErr := parseTemplate("session_id", raw, funcs)
-	if err := ctx.Err(); err != nil {
-		return "", err
-	}
-	if parseErr != nil {
-		return "", fmt.Errorf("%w: session_id: %v", ErrInvalidTemplate, parseErr)
-	}
-	return executeSessionTemplate(ctx, tmpl, vars)
-}
-
 func renderCompiledSessionID(ctx context.Context, compiled *template.Template, funcs template.FuncMap, vars map[string]string) (string, error) {
 	if err := ctx.Err(); err != nil {
 		return "", err