From 9d014fc5208f6489e6b08fb8f8ad9169281f7d52 Mon Sep 17 00:00:00 2001
From: Elman Badalov <40571118+thebadalov@users.noreply.github.com>
Date: Sat, 24 Oct 2026 18:17:42 +0400
Subject: [PATCH] fix(idempotency): keep the payload hash when completing
 records in the Redis layer

CachePersistenceLayer._update_record overwrote the record with a new SET
that only had data, status and expiration, dropping the validation hash
written by _put_in_progress_record. With payload_validation_jmespath set,
a retry with the same payload then raised IdempotencyValidationError
instead of returning the stored response.

Write the validation key in _update_record when payload validation is
enabled, as the DynamoDB layer already does.
---
 .../idempotency/persistence/redis.py          |  4 +++
 .../idempotency/_redis/test_redis_layer.py    | 33 +++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/aws_lambda_powertools/utilities/idempotency/persistence/redis.py b/aws_lambda_powertools/utilities/idempotency/persistence/redis.py
index 7b4688beca7..bc3d626f3c6 100644
--- a/aws_lambda_powertools/utilities/idempotency/persistence/redis.py
+++ b/aws_lambda_powertools/utilities/idempotency/persistence/redis.py
@@ -492,6 +492,10 @@ def _update_record(self, data_record: DataRecord) -> None:
                 self.expiry_attr: data_record.expiry_timestamp,
             },
         }
+
+        if self.payload_validation_enabled:
+            item["mapping"][self.validation_key_attr] = data_record.payload_hash
+
         logger.debug(f"Updating record for idempotency key: {data_record.idempotency_key}")
         encoded_item = self._json_serializer(item["mapping"])
         ttl = self._get_expiry_second(data_record.expiry_timestamp)
diff --git a/tests/functional/idempotency/_redis/test_redis_layer.py b/tests/functional/idempotency/_redis/test_redis_layer.py
index e83d2603b61..254ca94f580 100644
--- a/tests/functional/idempotency/_redis/test_redis_layer.py
+++ b/tests/functional/idempotency/_redis/test_redis_layer.py
@@ -615,6 +615,39 @@ def lambda_handler(event, context):
         lambda_handler(mock_event, lambda_context)
 
 
+def test_idempotent_function_and_lambda_handler_redis_validation_same_payload(
+    persistence_store_standalone_redis: RedisCachePersistenceLayer,
+    lambda_context,
+):
+    mock_event = {"user_id": "xyz", "time": "1234"}
+    persistence_layer = persistence_store_standalone_redis
+    expected_result = {"message": "Foo"}
+    config = IdempotencyConfig(event_key_jmespath="user_id", payload_validation_jmespath="time")
+    calls = 0
+
+    @idempotent(persistence_store=persistence_layer, config=config)
+    def lambda_handler(event, context):
+        nonlocal calls
+        calls += 1
+        return expected_result
+
+    # WHEN calling the handler with payload validation enabled
+    first_result = lambda_handler(mock_event, lambda_context)
+
+    # THEN the completed record keeps the payload hash
+    stored_record = json.loads(next(iter(persistence_layer.client.cache.values())))
+    assert stored_record["status"] == "COMPLETED"
+    assert stored_record[persistence_layer.validation_key_attr]
+
+    # WHEN calling the handler again with the same payload
+    second_result = lambda_handler(mock_event, lambda_context)
+
+    # THEN the stored response is returned without running the handler again
+    assert first_result == expected_result
+    assert second_result == expected_result
+    assert calls == 1
+
+
 def test_idempotent_function_and_lambda_handler_redis_basic_no_decode(
     persistence_store_standalone_redis_no_decode: RedisCachePersistenceLayer,
     lambda_context,