A rest opening or closing a bar must use the single largest legal value reaching the nearest primary beat or the barline, not remain fragmented

A rest immediately after a barline (opening a bar) and a rest immediately before the next barline (closing a bar) are exactly the positions where the general consolidation rule above is most visible to a reader — an un-consolidated bar-edge rest run reads as sloppy engraving even when each individual rest is otherwise legal, because a reader's eye lands on bar edges first when scanning for silence.

A 4/4 bar whose only content is two eighth rests followed by a half note, i.e. the bar OPENS with `e, e` where a single `q` rest would do (and the run starts exactly on the downbeat, a quarter-grid position) — legal per rest-no-cross-primary-beat but not consolidated.

Gould, Behind Bars, ch. 'Rests'; Read, Music Notation, rest-placement conventions at bar boundaries.

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