Stem shortening below the standard length has no code path in Gradus's current pipeline — treat any occurrence as a distinct, deliberate API call

In dense chord voicings, engravers occasionally trim a stem slightly for legibility, but never below a practical floor of roughly 2.5-3 staff-spaces.

A rendered stem measurably shorter than the calibrated floor would require some future code path to call `setStemLength()` (or set `stem_extension_override`) with a negative value; no such call exists today.

Ross, The Art of Music Engraving, stem-length section (practical minimum for legibility).

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