The leading tone in minor is always spelled as the raised 7th scale-degree letter, never its flat-side enharmonic equivalent

In harmonic and melodic minor, the leading tone is spelled as the letter a diatonic 2nd below tonic (e.g. A minor's leading tone is G#, never Ab, since Ab is a diminished 2nd/near-unison from A).

A cadential V-i in A minor spells the leading tone Ab4 instead of G#4.

Gould, spelling-by-function principle; universal tonal-harmony-pedagogy convention, directly relevant to Gradus's own chorale-harmony/roman-numeral curriculum. No disagreement among authorities.

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