A tie or slur must not cross a repeat barline

A tie or slur written across a repeat barline is ambiguous: on the first pass it connects to the material after the repeat sign, but on the repeated pass it would need to connect back to the start of the repeated section — a different note. Standard practice re-articulates instead (no tie) or uses a different device (a footnote, or simply not tying).

The last note of a measure whose `barlineEnd === 'repeat-end'` has `tiedToNext: true` (or `slurEnd`/`slurStart` spanning across it) into the first note of the FOLLOWING measure, which on the repeat pass is actually reached from the start of the repeated section, not from the tied note.

Gould, Behind Bars, ch. Repeat Barlines, and Ross, The Art of Music Engraving, both caution against tying/slurring across a repeat sign for exactly this ambiguity.

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