Function show_model_input 

pub async fn show_model_input(agent: &mut SdkAgent, prompt: &str) -> Value

BP-5 (catalog D2 “Prompt-input debugging”): render the exact model-visible input prompt would produce, as JSON, without sending anything.

The prompt is expanded exactly as submit_agent would expand it and the request is assembled by the loop’s own chat_request, so this is the real input rather than a second rendering of it. Nothing is recorded, nothing is persisted, and no provider request is issued.