Preserve cache control in rendered prompts

internal/prompt/go_renderer.go

@@ -75,8 +75,9 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 		}
 
 		renderedMessages = append(renderedMessages, domain.RenderedMessage{
-			Role:    tmplMsg.Role,
-			Content: buf.String(),
+			Role:         tmplMsg.Role,
+			Content:      buf.String(),
+			CacheControl: cloneCacheControl(tmplMsg.CacheControl),
 		})
 	}
 
@@ -84,3 +85,11 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 		Messages: renderedMessages,
 	}, nil
 }
+
+func cloneCacheControl(in *domain.CacheControl) *domain.CacheControl {
+	if in == nil {
+		return nil
+	}
+	out := *in
+	return &out
+}