Function render_prompt_tool_carrier 

pub fn render_prompt_tool_carrier(
    body: &str,
    attachments: &[RenderedMarker],
) -> String

Render a prompt-mode carrier: prefix, count header, marker lines, body.

Zero attachments render as a [Tool attachments: 0] count line and the body starting on line 3, so a body whose own first line is a fake count header stays body — the real count line above it already said zero.