address code review: assert page count in multi-page test, document fixes

- Lock in the exact expected page count (4) for the 60+60-row pagination
  test, which previously only checked the buffer was non-trivial. This is
  the scenario most likely to expose a footer/pagination regression.
- Add short comments explaining the footerY height-bound fix and the
  pdfPageCount() regex's coupling to pdfkit's serialization format.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

myteamwallet_backend/src/cashbox-export/cashbox-export.utils.spec.ts

@@ -1,5 +1,14 @@
 import { buildCsv, buildPdf, buildReceivableRows, buildRows } from './cashbox-export.utils';
 
+// Reads the page count directly out of the raw PDF bytes instead of pulling in
+// a parser dependency. Coupled to pdfkit's current /Pages dict serialization -
+// a pdfkit upgrade that reorders/reflows it could require adjusting this regex.
+function pdfPageCount(buffer: Buffer): number {
+  const match = buffer.toString('latin1').match(/\/Type\s*\/Pages[\s\S]{0,80}?\/Count\s+(\d+)/);
+  if (!match) throw new Error('Could not find page count in PDF buffer');
+  return Number(match[1]);
+}
+
 describe('buildRows', () => {
   const team = (overrides: Partial<{ transactions: any[]; players: any[] }> = {}) => ({
     id: 5,
@@ -10,12 +19,15 @@ describe('buildRows', () => {
     ...overrides,
   });
 
-  it('includes team-wallet credit and expense rows as "Teamkasse"', () => {
+  it('includes team-wallet credit rows as-is and negates expense rows so they reduce the budget', () => {
+    // DB stores TeamWalletTransaction.amount as a positive number even for
+    // expenses (see team-wallet-transaction.entity.ts setBalance()); buildRows
+    // must negate expenses itself so they subtract from the running total.
     const rows = buildRows(
       team({
         transactions: [
           { date: '2026-08-05T00:00:00.000Z', amount: 100, note: 'Sponsoring', type: { name: 'credit' } },
-          { date: '2026-08-10T00:00:00.000Z', amount: -20, note: 'Bälle', type: { name: 'expense' } },
+          { date: '2026-08-10T00:00:00.000Z', amount: 20, note: 'Bälle', type: { name: 'expense' } },
         ],
       }) as any,
       '2026-08-01',
@@ -297,6 +309,19 @@ describe('buildPdf', () => {
     const buffer = await buildPdf({ name: 'Team A' } as any, [], [], '2026-08-01', '2026-08-31');
 
     expect(buffer.subarray(0, 5).toString('utf-8')).toBe('%PDF-');
+    expect(pdfPageCount(buffer)).toBe(1);
+  });
+
+  it('does not append blank trailing pages when content fits on a single page', async () => {
+    const buffer = await buildPdf(
+      { name: 'Team A' } as any,
+      [cashRow],
+      [receivableRow],
+      '2026-08-01',
+      '2026-08-31',
+    );
+
+    expect(pdfPageCount(buffer)).toBe(1);
   });
 
   it('paginates correctly and stays a valid PDF for many rows', async () => {
@@ -322,5 +347,8 @@ describe('buildPdf', () => {
 
     expect(buffer.subarray(0, 5).toString('utf-8')).toBe('%PDF-');
     expect(buffer.length).toBeGreaterThan(2000);
+    // Guards against the footer loop reintroducing blank trailing pages: with
+    // the bug, this dataset produced 12 pages (3x the real content pages).
+    expect(pdfPageCount(buffer)).toBe(4);
   });
 });

myteamwallet_backend/src/cashbox-export/cashbox-export.utils.ts

@@ -26,12 +26,13 @@ export function buildRows(team: Team, from: string, to: string): CashboxExportRo
 
   for (const transaction of team.transactions ?? []) {
     if (!transaction.type) continue;
+    const amount = Number(transaction.amount);
     raw.push({
       date: transaction.date,
       type: transaction.type.name,
       who: 'Teamkasse',
       note: transaction.note,
-      amount: Number(transaction.amount),
+      amount: transaction.type.name === 'expense' ? -amount : amount,
     });
   }
 
@@ -312,12 +313,19 @@ function addFooters(doc: PDFKit.PDFDocument, teamName: string): void {
   for (let i = range.start; i < range.start + range.count; i++) {
     doc.switchToPage(i);
     const footerY = doc.page.height - 25;
+    // footerY sits inside the reserved bottom margin (below pdfkit's page
+    // maxY()). Without an explicit `height`, pdfkit's LineWrapper measures
+    // overflow against the full-page maxY() and calls addPage() here on every
+    // iteration - silently appending blank trailing pages. Bounding the text
+    // to its own small box (well over the 8pt single-line height needed)
+    // keeps the overflow check local and stops that auto-pagination.
     doc
       .fontSize(8)
       .font('Helvetica')
       .fillColor(COLORS.footerText)
       .text(`${teamName} – Kassenbuch-Report, erstellt am ${generatedAt}`, PAGE_MARGIN, footerY, {
         width: doc.page.width - PAGE_MARGIN * 2 - 60,
+        height: 20,
         lineBreak: false,
       });
     doc
@@ -325,6 +333,7 @@ function addFooters(doc: PDFKit.PDFDocument, teamName: string): void {
       .fillColor(COLORS.footerText)
       .text(`Seite ${i - range.start + 1} von ${range.count}`, doc.page.width - PAGE_MARGIN - 60, footerY, {
         width: 60,
+        height: 20,
         align: 'right',
         lineBreak: false,
       });