Model A cannot author ANY repeat structure beyond a single whole-block repeat pair

Full repeat-structure notation (mid-piece repeat barlines, first/second endings, D.C./D.S./coda/segno) is standard for fugue expositions, Baroque dance forms, and sectional chorale settings — all genres Gradus's curriculum explicitly teaches.

Gould, Behind Bars, ch. Repeat Barlines and ch. Repeat Marks — these devices are described as ordinary, frequently-needed notation, not advanced/rare cases, for exactly the repertoire (fugue, Baroque forms, chorale) Gradus's curriculum covers.

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