fix: reduce pending payment polling rate

tests/unit/test_tasks.py

@@ -29,3 +29,51 @@ async def test_process_invoice_returns_payment_failed_on_failed_status(monkeypat
     assert result["error"]["code"] == "PAYMENT_FAILED"
     assert result["error"]["message"] == "Payment failed."
     assert result["in_budget"] is True
+
+
+@pytest.mark.asyncio
+async def test_process_invoice_polls_pending_payment_at_sustainable_interval(
+    monkeypatch,
+):
+    async def fake_tracked_spend_nwc(*args, **kwargs):
+        return True, "a" * 64
+
+    statuses = iter(
+        [
+            SimpleNamespace(success=False, failed=False),
+            SimpleNamespace(
+                success=True,
+                failed=False,
+                preimage="b" * 64,
+                fee_msat=10,
+                paid=True,
+            ),
+        ]
+    )
+
+    async def fake_check_transaction_status(wallet_id: str, payment_hash: str):
+        return next(statuses)
+
+    sleep_calls = []
+
+    async def fake_sleep(delay: float):
+        sleep_calls.append(delay)
+
+    monkeypatch.setattr(tasks, "tracked_spend_nwc", fake_tracked_spend_nwc)
+    monkeypatch.setattr(
+        tasks, "check_transaction_status", fake_check_transaction_status
+    )
+    monkeypatch.setattr(tasks.asyncio, "sleep", fake_sleep)
+
+    result = await tasks._process_invoice(
+        wallet_id="wallet123",
+        pubkey="a" * 64,
+        invoice="lnbc1example",
+        amount_msats=1000,
+        description="test",
+    )
+
+    assert sleep_calls == [tasks.PAYMENT_STATUS_POLL_INTERVAL_SECONDS]
+    assert result["preimage"] == "b" * 64
+    assert result["fee_msats"] == 10
+    assert result["paid"] is True