Incipit — opening-bars reference snippet

An incipit is a short (2-6 note) excerpt of a melody's opening, notated without a full time/key-signature commitment, used purely as a label/identifier. It is explicitly NOT meant to be played through as a complete musical statement.

Not representable as a distinct device — a short `notes` array could fake it, but nothing marks it as 'this is a label snippet,' so it is indistinguishable from an unusually short real exercise and might get graded/played/looped as complete.

Gould (Behind Bars, incipit conventions in reference/thematic contexts); standard musicological/thematic-catalogue practice.

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