The number of bars per system must be chosen by that system's own note density, not a single fixed count applied to the whole block

Gould is explicit that the number of measures per line is governed by how much content those measures contain, not a target count decided in advance — a system of eighth-note-dense bars legitimately holds fewer bars than a system of half-note-sparse bars, on the SAME page.

`barsPerSystem` (declared ~line 334, used lines 719-721) is a SINGLE number applied uniformly across the ENTIRE block via `systemBeats = barsPerSystem * beatsPerBar` — there is no mechanism for system 1 to hold 4 bars of sparse half notes while system 2 holds 2 bars of dense sixteenth-note runs, which is exactly what good engraving would choose for genuinely uneven-density content (a common shape in fugue expositions, alternating slow subject entries with faster episodic material).

Gould, Behind Bars, system-layout chapter (bars-per-system determined by content density, an explicit per-line editorial judgment); Ross, The Art of Music Engraving (same principle, framed around avoiding both cramped and sparse lines).

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