Add attention inbox and AI usage observability

tests/outbox.test.ts

@@ -70,4 +70,17 @@ describe('DeliveryOutboxRepository', () => {
     expect(outbox.markSent(delivery.id, 'worker-a', sentMessageId, 130)).toBe(true);
     expect(outbox.get(delivery.id)).toMatchObject({ status: 'sent', sentMessageId, leaseOwner: null });
   });
+
+  it('surfaces failed deliveries for the attention inbox', () => {
+    const delivery = outbox.discover({
+      postId: 'post-1', recipient: 'recipient', subject: 'subject', message: 'message', idempotencyKey: 'post-1:v1', now: 100,
+    });
+    outbox.markPrepared(delivery.id, 110);
+    outbox.claim(delivery.id, 'worker-a', 50, 120);
+    outbox.markFailed(delivery.id, 'worker-a', 'Reddit rejected the invitation', 130);
+
+    expect(outbox.getFailed()).toEqual([
+      expect.objectContaining({ id: delivery.id, status: 'failed', lastError: 'Reddit rejected the invitation' }),
+    ]);
+  });
 });