Function diagnostics_help 

pub fn diagnostics_help(layer: &DiagnosticsLayer) -> HelpContent

Build a help buffer listing every workspace diagnostic (Phase 4.1.d.iv). Each diagnostic renders as one [severity] [path:line:col message](file:path:line) row – the markdown link is parsed by extract_links_and_clean into a HelpLinkTarget::Source that the existing do_help_follow_link path knows how to dispatch (jumps to the file at the given line).

URIs sort alphabetically; diagnostics within a URI sort by (line, column). Empty layer renders an explicit “no diagnostics” message so the buffer is always useful as a status read.