Ornament glyphs (trill, turn, mordent) need horizontal room above the note distinct from the notehead's own footprint

An ornament glyph sits above the staff and can be visually wider than the notehead it decorates — if the note's own spacing doesn't leave room, the ornament collides with the ornament (or accidental, or slur) on the adjacent note. A sustained trill additionally draws a wavy extension line for its full duration, a horizontal-space commitment the note's own duration-based space may not otherwise provide.

`n.ornament` (lines 1025-1033) maps to a single VexFlow `Ornament` glyph ('tr', 'turn', 'mordent') with NO wavy trill-extension-line support at all (Gradus's ornament model is a single point-glyph, not a duration-spanning one), and — as with grace notes — the pre-render width estimate has no ornament term whatsoever.

Gould, Behind Bars, ornaments chapter (trill-extension-line spacing); Ross, The Art of Music Engraving (ornament clearance rules); SMuFL/Bravura glyph metrics measured directly.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.