A trill needing a chromatic auxiliary must show the accidental above the trill sign

When the diatonic upper auxiliary of a trill needs raising or lowering to match the harmony (routine in Bach), a small accidental is printed directly above the `tr` sign.

A trill on scale-degree 7 in a minor key needs its upper auxiliary raised a semitone (the leading-tone trill), but `ornament: 'trill'` (Model A) or `ornament: 'trill'` (Model C) has no accompanying accidental field anywhere — the tool can add the `tr` glyph but never the qualifying accidental.

Gould, Behind Bars, ch. Ornaments — shows the accidental-above-trill convention explicitly; this is standard Baroque engraving practice directly relevant to Gradus's Bach-chorale and fugue curriculum.

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