Support for Lending Protocol (XLS-66d) (#866)

* Models and unit tests for LP amendment; 
* fix: add PermissionDelegationV1_1 amendment into the config file for explicit inclusion

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: ckeshava

.ci-config/rippled.cfg

@@ -201,10 +201,11 @@ PermissionedDomains
 SingleAssetVault
 fixFrozenLPTokenTransfer
 fixInvalidTxFlags
-PermissionDelegationV1_1
 PermissionedDEX
 Batch
 TokenEscrow
+LendingProtocol
+PermissionDelegationV1_1
 
 # This section can be used to simulate various FeeSettings scenarios for rippled node in standalone mode
 [voting]

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [[Unreleased]]
 
+### Added
+- Support for the Lending Protocol (XLS-66d)
+
 ## [[4.3.1]] - 2025-11-12
 
 ### Added

tests/integration/reqs/test_sign.py

@@ -0,0 +1,45 @@
+from tests.integration.integration_test_case import IntegrationTestCase
+from tests.integration.it_utils import fund_wallet_async, test_async_and_sync
+from xrpl.asyncio.transaction import autofill_and_sign
+from xrpl.models.requests import Sign
+from xrpl.models.transactions import LoanSet
+from xrpl.wallet import Wallet
+
+_SECRET = "randomsecretkey"
+_LOAN_BROKER_ID = "D1B9DFF432B4F56127BE947281A327B656F202FC1530DD6409D771F7C4CA4F4B"
+_COUNTERPARTY_ADDRESS = "rnFRDVZUV9GmqoUJ65gkaQnMEiAnCdxb2m"
+
+
+class TestSign(IntegrationTestCase):
+    @test_async_and_sync(globals(), ["xrpl.transaction.autofill_and_sign"])
+    async def test_basic_functionality(self, client):
+        loan_issuer = Wallet.create()
+        await fund_wallet_async(loan_issuer)
+
+        loan_issuer_signed_txn = await autofill_and_sign(
+            LoanSet(
+                account=loan_issuer.address,
+                loan_broker_id=_LOAN_BROKER_ID,
+                principal_requested="100",
+                counterparty=_COUNTERPARTY_ADDRESS,
+            ),
+            client,
+            loan_issuer,
+        )
+        response = await client.request(
+            Sign(
+                transaction=loan_issuer_signed_txn,
+                signature_target="CounterpartySignature",
+                secret=_SECRET,
+            )
+        )
+        self.assertTrue(response.is_successful())
+        self.assertTrue(response.result["tx_json"]["CounterpartySignature"] is not None)
+        self.assertTrue(
+            response.result["tx_json"]["CounterpartySignature"]["SigningPubKey"]
+            is not None
+        )
+        self.assertTrue(
+            response.result["tx_json"]["CounterpartySignature"]["TxnSignature"]
+            is not None
+        )