Stems must maintain a minimum length where they meet the beam

A note's stem, when extended to reach a sloped or multi-level beam, must not be shortened below a legible minimum length, and multi-level (16th+) beams require progressively longer stems to accommodate each additional beam stroke.

A note's stem is rendered so short under a steep beam slope that the notehead and beam nearly touch, or a 32nd-note group's stem doesn't lengthen enough to clear three beam strokes plus spacing.

Gould, Behind Bars, ch. Beaming/Stems — minimum stem length under beams; Ross, Art of Music Engraving — same, with explicit guidance that stem shortening has a floor. VexFlow's own baseline is `Tables.STEM_HEIGHT = 35` VexFlow units (`tables.ts` line 545) — 3.5 staff-spaces, since `Tables.STAVE_LINE_DISTANCE = 10` (line 573).

This rule is about where marks land on the page, so it can only be judged after engraving. Collision and spacing faults live here.