Function groupTraces

packages/cli/src/commands/keyframes.ts:529–554

(tweens: SurfacedTween[])

// (not drawn). Only targets with ≥2 strokes become a composited trace; a single
// stroke stays on the normal per-tween path so existing output is unchanged.
function groupTraces(tweens: SurfacedTween[]): SurfacedTrace[] {
  const byTarget = new Map<string, SurfacedTween[]>();
  for (const t of tweens) {
    if (t.method === "set") continue;
    if (!t.path || t.path.length < 2) continue;
    if (!pathTravels(t.path)) continue; // in-place tween (e.g. opacity carrying a static y) is not a drawn stroke
    const list = byTarget.get(t.target);
    if (list) list.push(t);
    else byTarget.set(t.target, [t]);
  }
  const traces: SurfacedTrace[] = [];
  for (const [target, list] of byTarget) {
    if (list.length < 2) continue;
    const strokes = [...list]
      .sort((a, b) => a.start - b.start)
      .map((t) => ({
        id: t.id,
        start: t.start,
        end: t.end,
        keyframes: t.keyframes,
        points: t.path!,
      }));
    traces.push({ target, strokes });
  }
  return traces;
}

function collectCompositions(indexPath: string): SurfacedComposition[] {
  const html = readFileSync(indexPath, "utf-8");