Multiple grace notes in one group must be beamed together with an explicit boundary, not left to auto-beam heuristics

When 2+ grace notes precede one principal note, they are beamed together as a single figure; the beam must not extend into or merge with a neighboring grace group belonging to a DIFFERENT principal note.

Gould, Behind Bars, ch. Grace Notes — multiple grace notes are always beamed as one group, never given individual flags; Ross, The Art of Music Engraving, shows the same grouping convention.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.