Tie and slur curvature already follows stem direction automatically in VexFlow — which means it also inherits any stem-direction bug

A tie or slur curves away from the stem — above the notehead for a stem-down note, below for a stem-up note — so the curve doesn't cross or crowd the stem.

Because curvature direction is read directly from `note.getStemDirection()` rather than independently computed, any note whose stem direction is wrong (per `stem-direction-clef-middle-line-pivot` or the SATB-forced-but-wrong-value case) produces a tie or slur curving on the WRONG side as a direct, mechanical consequence — this is not a separate bug to fix in `StaveTie`/`Curve`, it is a symptom of the upstream stem-direction bug propagating one hop further.

Gould, Behind Bars, Ties and Slurs chapters (opposite-stem default).

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