Draw paylines yourself from win:group

The minimum code

const lineLayer = new PIXI.Container();
reelSet.addChild(lineLayer);

reelSet.events.on('win:group', (win, cells) => {
  const gfx = new PIXI.Graphics();
  const pts = cells.map(c => {
    const b = reelSet.getCellBounds(c.reelIndex, c.rowIndex);
    return { x: b.x + b.width / 2, y: b.y + b.height / 2 };
  });
  gfx.moveTo(pts[0].x, pts[0].y);
  for (let i = 1; i < pts.length; i++) gfx.lineTo(pts[i].x, pts[i].y);
  gfx.stroke({ color: paletteFor(win), width: 6 });
  lineLayer.addChild(gfx);
  fadeOutAfter(gfx, 1200);
});

const presenter = new WinPresenter(reelSet);   // no line drawing in core
await presenter.show(wins);

Why events, not an injected renderer

Overlays vary: payline polylines, cluster outlines, numbered badges, Spine line rigs, particle trails. Baking any one into the core API would either force a single look on every game, or grow a config surface that outlasts the feature. Events plus reelSet.getCellBounds keeps the decision on your side. draw whatever fits the art.

The event contract

Dim is applied before win:group fires, so a listener taking a snapshot sees the live state.