Capture an immutable rate-quote snapshot for disclosure

Pricing-derived TRID disclosure fields (rate, points, lender credit) should reference an immutable quote snapshot. The pattern:

// At the moment of disclosure
const quote = await ratestack.pricing(input, { mode: "BEST_EX" });
const snapshot = {
  quoteId: quote.id,
  ratesheetVersion: quote.ratesheetVersion,
  capturedAt: new Date().toISOString(),
  correlationId: quote.correlationId,
  // The full trace for audit reproducibility
  trace: quote.bestEx.adjustments,
};
// Persist the snapshot keyed to the LE/CD record
await db.disclosures.insert({ leId, cdId, snapshot });

// To reproduce later: replay against the captured ratesheetVersion
const replayed = await ratestack.pricing(input, {
  mode: "BEST_EX",
  asOf: snapshot.capturedAt,  // engine resolves the active ratesheet at that time
});
// replayed.bestEx.finalPrice should equal the disclosed price

The replay endpoint guarantees reproduction so long as the underlying ratesheet versions remain accessible (indefinite retention is the default).