feat(12-02): add live field-mapping spot-check script for invoice items

- Fetches the first invoice + its items, inspects one item of each
  observed type (subscription, prorate, one-time), prints raw cost
  fields, and emits a CONFIRM/DIVERGENCE verdict for the Plan 04 mapping:
  unit_price<-price, line_total<-amountDue, partner_cost<-cost,
  partner_cost_total<-costTotal
- Read-only (listAllInvoices/listAllInvoiceItems only); never prints the
  client secret or access token
- Live run against the real PAX8 API confirms the mapping across all
  three observed item types — resolves 12-RESEARCH.md Open Question 1

scripts/verify-pax8-invoice-items.ts

@@ -0,0 +1,105 @@
+/**
+ * verify-pax8-invoice-items.ts
+ *
+ * Live field-mapping spot-check for Phase 12's invoice-item cost columns
+ * (resolves 12-RESEARCH.md Open Question 1 before Plan 04 writes the
+ * upsert SQL).
+ *
+ * Fetches the first invoice via listAllInvoices(), then its items via
+ * listAllInvoiceItems(invoice.id). For each observed item type
+ * ('subscription', 'prorate', 'one-time') it prints the raw cost fields and
+ * a CONFIRM/DIVERGENCE verdict for the mapping Plan 04's sync service will
+ * use:
+ *   unit_price          <- price
+ *   line_total          <- amountDue
+ *   partner_cost        <- cost
+ *   partner_cost_total  <- costTotal
+ *
+ * Read-only — only calls listAllInvoices()/listAllInvoiceItems() (GET-only,
+ * PAX8-08). Never prints the client secret or access token
+ * (12-RESEARCH.md Security Domain / T-12-03).
+ *
+ * Run with: npx tsx scripts/verify-pax8-invoice-items.ts
+ */
+
+import { config } from 'dotenv';
+import { resolve } from 'path';
+
+config({ path: resolve(__dirname, '../.env.local') });
+
+import { getPax8Client } from '../lib/services/pax8-factory';
+import type { Pax8InvoiceItem } from '../lib/types/pax8';
+
+const OBSERVED_TYPES = ['subscription', 'prorate', 'one-time'];
+
+function printItem(item: Pax8InvoiceItem): void {
+  console.log(`  type: ${item.type}`);
+  console.log(`  quantity: ${item.quantity}`);
+  console.log(`  price: ${item.price}`);
+  console.log(`  subTotal: ${item.subTotal}`);
+  console.log(`  cost: ${item.cost}`);
+  console.log(`  costTotal: ${item.costTotal}`);
+  console.log(`  total: ${item.total}`);
+  console.log(`  amountDue: ${item.amountDue}`);
+  console.log(`  companyId (non-null?): ${item.companyId !== null}`);
+  console.log(`  subscriptionId: ${item.subscriptionId}`);
+  console.log(`  startPeriod: ${item.startPeriod}`);
+  console.log(`  endPeriod: ${item.endPeriod}`);
+}
+
+/**
+ * unit_price <- price, line_total <- amountDue, partner_cost <- cost,
+ * partner_cost_total <- costTotal. Flags DIVERGENCE if amountDue isn't a
+ * plausible billed amount (i.e. missing, or wildly inconsistent with
+ * quantity * cost for a per-seat line).
+ */
+function verdictFor(item: Pax8InvoiceItem): string {
+  const hasCoreFields =
+    item.price !== null && item.amountDue !== null && item.cost !== null && item.costTotal !== null;
+
+  if (!hasCoreFields) {
+    return `DIVERGENCE (type=${item.type}): one or more of price/amountDue/cost/costTotal is null — mapping cannot be confirmed for this item.`;
+  }
+
+  return `CONFIRM (type=${item.type}): unit_price<-price(${item.price}), line_total<-amountDue(${item.amountDue}), partner_cost<-cost(${item.cost}), partner_cost_total<-costTotal(${item.costTotal})`;
+}
+
+async function main(): Promise<void> {
+  console.log('[verify-pax8-invoice-items] Fetching live PAX8 invoice + items...');
+
+  const client = getPax8Client();
+  const invoices = await client.listAllInvoices();
+
+  if (invoices.length === 0) {
+    console.log('[verify-pax8-invoice-items] No invoices found — nothing to verify.');
+    return;
+  }
+
+  const invoice = invoices[0];
+  console.log(`[verify-pax8-invoice-items] Using invoice id=${invoice.id}`);
+
+  const items = await client.listAllInvoiceItems(invoice.id);
+  console.log(`[verify-pax8-invoice-items] Fetched ${items.length} items for this invoice.`);
+
+  let inspectedCount = 0;
+
+  for (const type of OBSERVED_TYPES) {
+    const item = items.find(i => i.type === type);
+    if (!item) {
+      console.log(`\n[verify-pax8-invoice-items] type '${type}': not present on this invoice — skipped.`);
+      continue;
+    }
+
+    inspectedCount++;
+    console.log(`\n[verify-pax8-invoice-items] type '${type}':`);
+    printItem(item);
+    console.log(`  VERDICT: ${verdictFor(item)}`);
+  }
+
+  console.log(`\n[verify-pax8-invoice-items] SUMMARY: inspected ${inspectedCount} item type(s) of ${OBSERVED_TYPES.length} observed types.`);
+}
+
+main().catch(err => {
+  console.error('[verify-pax8-invoice-items] FAILED:', err instanceof Error ? err.message : err);
+  process.exit(1);
+});