feat(12-02): add listAllInvoices and listAllInvoiceItems to Pax8Client

- listAllInvoices() pages the flat /invoices header list via paginateAll
- listAllInvoiceItems(invoiceId) pages the nested per-invoice
  /invoices/{id}/items child resource
- Both GET-only, reusing the existing paginateAll helper (PAX8-08)
- Note: no /orders call added (12-RESEARCH.md Pitfall 3 — unreliable/504s)
- Log pre-existing unrelated sync-scheduler.ts TS2307 errors to
  deferred-items.md (appgate-factory/appgate-sync-service not in this
  worktree's git history)

.planning/phases/12-orders-invoices-company-matching/deferred-items.md

@@ -15,3 +15,9 @@ Out-of-scope issues discovered during execution but not fixed (per Scope Boundar
   `lib/types/pax8.ts` reverted to its pre-plan state. Not touched by
   migrations/093 or lib/types/pax8.ts. Someone completing the appgate feature
   branch/commit should resolve this; out of scope for Phase 12.
+
+## Plan 02
+
+- Same pre-existing `sync-scheduler.ts:446`/`:450` TS2307 errors reproduce
+  unchanged after Task 1's `pax8-client.ts` edits (`listAllInvoices` /
+  `listAllInvoiceItems`). Confirmed unrelated to this plan's files.

lib/services/pax8-client.ts

@@ -4,7 +4,14 @@
  * https://devx.pax8.com
  */
 
-import type { Pax8Company, Pax8PageEnvelope, Pax8Subscription, Pax8Product } from '@/lib/types/pax8';
+import type {
+  Pax8Company,
+  Pax8PageEnvelope,
+  Pax8Subscription,
+  Pax8Product,
+  Pax8Invoice,
+  Pax8InvoiceItem,
+} from '@/lib/types/pax8';
 
 export interface Pax8ClientConfig {
   clientId: string;
@@ -120,4 +127,30 @@ export class Pax8Client {
       this.fetchJson<Pax8PageEnvelope<Pax8Product>>(`/products?page=${page}&size=${size}`),
     );
   }
+
+  /**
+   * Read-only: page through every invoice header (PAX8-08 — GET only).
+   * `/invoices` is the partner's own consolidated monthly bill — one row per
+   * billing period, not per end-customer (12-RESEARCH.md Pitfall 1). Do NOT
+   * add an orders-endpoint call — it is unreliable (504s) for this account
+   * (12-RESEARCH.md Pitfall 3).
+   */
+  async listAllInvoices(): Promise<Pax8Invoice[]> {
+    return this.paginateAll<Pax8Invoice>((page, size) =>
+      this.fetchJson<Pax8PageEnvelope<Pax8Invoice>>(`/invoices?page=${page}&size=${size}`),
+    );
+  }
+
+  /**
+   * Read-only: page through every line item of a single invoice
+   * (PAX8-08 — GET only). Invoice items are a per-invoice child resource —
+   * there is no flat `/invoice-items` endpoint (12-RESEARCH.md Pitfall 2).
+   */
+  async listAllInvoiceItems(invoiceId: string): Promise<Pax8InvoiceItem[]> {
+    return this.paginateAll<Pax8InvoiceItem>((page, size) =>
+      this.fetchJson<Pax8PageEnvelope<Pax8InvoiceItem>>(
+        `/invoices/${invoiceId}/items?page=${page}&size=${size}`,
+      ),
+    );
+  }
 }