Function count_user_image_markers 

pub fn count_user_image_markers(messages: &[ChatMessage]) -> usize

Count image markers that originate from genuine user messages (i.e. inbound attachments), excluding tool-result carriers (role == "tool" and [Tool results] user messages).

Callers use this to distinguish “the user sent an image we cannot see” (which should surface a user-facing capability error so the attachment is not silently ignored) from “an image marker arrived only via a tool result” (e.g. image_info/screenshot/image_gen), which can degrade to text-only on a non-vision provider without misleading the user.