test(dogfood): the persona matrix hangs its invoice lines off an unpaid invoice

The admin payload control created a showcase_invoice_line under
firstId('showcase_invoice'), whichever invoice a limit-1 read returned.
With random ids that is a different invoice on every boot, and several
seeded invoices are paid. Since the showcase locks a paid invoice's lines
(its showcase_guard_paid_invoice_line_* hooks), the control answered 400
"This invoice is paid, so its lines are locked" on some boots and not
others.

The seeded parent is now chosen by the state the lock reads (status not
paid), the way the account above it is chosen by its rule. Every line the
file creates under a seeded invoice hangs off this one parent. The lock is
unchanged.

Claude-Session: https://claude.ai/code/session_01LmjU2x1faLZ39DVTFyVca6
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/qa/dogfood/test/showcase-crud-persona-matrix.dogfood.test.ts

@@ -324,7 +324,19 @@ describe('showcase: persona × CRUD-cell matrix (#9481)', () => {
     );
     seed.productId = await firstId('showcase_product');
     seed.projectId = await firstId('showcase_project');
-    seed.invoiceId = await firstId('showcase_invoice');
+    // NOT `firstId` either, for the same reason as the account: the showcase
+    // locks a PAID invoice's lines (its `showcase_guard_paid_invoice_line_*`
+    // hooks), so a line can be neither added under one nor removed from one.
+    // `firstId` takes whichever invoice a `limit: 1` read returns, and with
+    // random ids that is a different invoice on every boot — several seeded
+    // invoices are paid, so the admin control below failed on some boots and
+    // not others. Every line this file creates under a seeded invoice hangs
+    // off this one, so the parent is chosen by the state the lock reads.
+    seed.invoiceId = String(
+      (await ql.find('showcase_invoice', {
+        where: { status: { $ne: 'paid' } }, limit: 1, context: SYS,
+      }))?.[0]?.id ?? '',
+    );
     seed.expenseReportId = await firstId('showcase_expense_report');
     seed.teamId = await firstId('showcase_team');
     expect(