Function simplifyStable

test/compute-engine/fungrim-loops.test.ts:118–127

* simplify(simplify(x)): assert termination within the time budget, a stable * (idempotent) endpoint, and return the result + elapsed time.

(expr: ReturnType<ComputeEngine['box']>)

 * (idempotent) endpoint, and return the result + elapsed time.
 */
function simplifyStable(expr: ReturnType<ComputeEngine['box']>): {
  result: ReturnType<ComputeEngine['box']>;
  stable: boolean;
  elapsedMs: number;
} {
  const t0 = Date.now();
  const s1 = expr.simplify();
  const s2 = s1.simplify();
  return { result: s1, stable: s2.isSame(s1), elapsedMs: Date.now() - t0 };
}

// ---------------------------------------------------------------------------
// 1. Artifact inverse-pair invariant (standing test, §2.5 layer 1)