pub fn format_diagnostic_popup_lines(diags: &[Diagnostic]) -> Vec<(String, u8)>Expand description
L4b: format the cursor line’s diagnostics into one popup line each:
<severity glyph> <message> [source:code] (+N related). The glyph
is the BMP-fallback severity mark (degrade-safe per the icon-palette
rule); the message is collapsed to its first line. Empty input →
empty Vec (the host echoes “no diagnostics on line”).