Implement WHOIS referral chain collection and merging logic (fixes #11)

- Introduced `collectWhoisReferralChain` to gather WHOIS responses while avoiding contradictory data from registrars.
- Updated `lookupDomain` to utilize the new chain collection method, ensuring TLD responses are prioritized.
- Added `mergeWhoisRecords` function to consolidate WHOIS data from multiple sources.
- Enhanced tests for referral handling and merging behavior, ensuring accurate data retention across scenarios.

src/whois/referral.ts

@@ -46,6 +46,50 @@ export async function followWhoisReferrals(
   return current;
 }
 
+/**
+ * Collect the WHOIS referral chain starting from the TLD server.
+ * Always includes the initial TLD response; may include one or more registrar responses.
+ * Stops on contradiction (registrar claims availability) or failures.
+ */
+export async function collectWhoisReferralChain(
+  initialServer: string,
+  domain: string,
+  opts?: LookupOptions,
+): Promise<WhoisQueryResult[]> {
+  const results: WhoisQueryResult[] = [];
+  const maxHops = Math.max(0, opts?.maxWhoisReferralHops ?? 2);
+  const first = await whoisQuery(initialServer, domain, opts);
+  results.push(first);
+  if (opts?.followWhoisReferral === false || maxHops === 0) return results;
+
+  const visited = new Set<string>([normalize(first.serverQueried)]);
+  let current = first;
+  let hops = 0;
+  while (hops < maxHops) {
+    const next = extractWhoisReferral(current.text);
+    if (!next) break;
+    const normalized = normalize(next);
+    if (visited.has(normalized)) break;
+    visited.add(normalized);
+    try {
+      const res = await whoisQuery(next, domain, opts);
+      // If registrar claims availability while TLD indicated registered, stop.
+      const registeredBefore = !isWhoisAvailable(current.text);
+      const registeredAfter = !isWhoisAvailable(res.text);
+      if (registeredBefore && !registeredAfter) {
+        // Do not adopt or append contradictory registrar; keep authoritative TLD only.
+        break;
+      }
+      results.push(res);
+      current = res;
+    } catch {
+      break;
+    }
+    hops += 1;
+  }
+  return results;
+}
+
 function normalize(server: string): string {
   return server.replace(/^whois:\/\//i, "").toLowerCase();
 }